Select the Right Camera Lens Features

Focal length

Measured in millimeters, this represents the distance between the optical center of a lens and its focal plane. The lower the focal length, the wider your angle of view; the higher the focal length, the narrower the angle of view.

The focal length for the three lens types generally breaks down as follows:

• Standard lens: Standard camera lenses typically have a 50mm to 55mm focal length

• Wide-angle lens: Wide-angle scamera lense have a 18mm to 35mm focal length. Fish-eye lenses range from 6mm to 16mm.

• Telephoto lens: Telephoto camera lenses have a 80mm to 500mm focal length.

Zoom lens

Lenses have either fixed focal length lenses (35mm, 50mm) or zoom lenses, where focal length changes. For example, the Canon EF zoom lens offers a zoom from 75mm–300mm. Zoom allows you to get closer to your subject by magnifying the image; you move a ring to alter the focal length and zoom in or out.

Auto focus and manual focus

Auto focus (AF) lenses do the focusing for you automatically. Manual Focus (MF), on the other hand, allows you to manually focus the camera lens. The former obviously provides ease and simplicity, while the latter is good for focusing in low light and when you need to focus in very precise increments.

Some camera lenses offer both types of focus functionality. Auto focus can be turned off or on, letting you manually focus whenever you want.

Aperture

Latin for “opening,” aperture indicates how much light a camera lens lets through to the focal plane. The smaller the aperture number (f/2.8, for example), the more light a lens will let in, thus better controlling the brightness of the exposure. And the more light a lens allows through, the faster the shutter speed.

Most important in low-light, outdoor picture-taking situations, a lens’s aperture will usually increase along with the focal length of a zoom lens. Both aperture and focal length will usually appear on the barrel of the lens.

Professional Digital Cameras when evaluated for use on a light Microscope

I just find another old cameras article that's very well written. Is that right?

An overview of some
Professional Digital Cameras when evaluated for use on a light Microscope
originally published, Journal of Biological Photography 1998
updated Aug 2003

Introduction
This article is the outcome of the talk that was given at BioComm 97 in Reno, Nevada. Writing about digital cameras seems almost impossible with the continual release of new cameras almost weekly in conjunction with the dynamic state of affairs the industry is in. Specifics on this topic are almost meaningless and what is much more relevant are general trends and considerations for choosing and using high end digital cameras. In the end analysis, your organization's goals and services need to drive such an acquisition.

Background
The majority of my work is accomplished at the light microscope. For this reason, many of the concerns I have, revolve around problems found when working there. Some of the obvious concerns found in this application are chip resolution, contrast, image brightness, as well as the chip's spectral response to name a few. Given the difficulty in creating high quality silver halide photomicrographs, problems inherent to direct digital cameras might seem to only compound the challenge.

In the time since Reno, I would speculate that no less than 100 new articles on this topic have been written in the contemporary magazines. Additionally, I can share that in the time since that meeting, no less than 100 new cameras have been released and there are industry projections that no less than 70 new models will be released over the next year. Consequently, writing this piece has become like trying to catch an elusive dream. It's right there but always moving. This feeling is absolutely consisitent with the entire field of electronic imaging.

Overview & a brief history
When the abstract for the original talk was submitted, my issues were primarily focused on Technical issues. My interests resided in how different cameras functioned as well as how they performed under controlled circumstances at a light microscope. As the work evolved, what became more relevant to me was the issues that confront a person who might consider purchasing a camera for use in their work. What camera would serve as the best choice and why.

I am quite lucky in that as a faculty member at RIT, many of my former students work in positions where I can borrow cameras for demonstration and/or evaluation. For this reason, I can evaluate the pro's and con's of many cameras in side by side comparisons. Not so long ago, when direct digital cameras were "still video" technology, their resolution was so poor that the immediacy of image capture had minimal value to the Biomedical Photographer. It is also important to recall that this was not so long ago. It has been said by many that electronic photography has done in 7 years what it took silver halide technology 150 years to achieve. As it pertains to purchase, this causes a dilemma because there is never the right time to purchase such a powerful tool. As each month brings something new and better and cheaper, one needs to use their best guess as to when to jump in. These cameras do not come cheap either with the least expensive "professional" camera starting out at no less than $6K.

One of the most important considerations for acquiring this technology is not the capability of the cameras anymore, but rather what you are trying to do with the camera. In fact, pictures made from Kodak 35mm Ektachrome 64T film and those created on quality direct digital cameras are very hard to differentiate. Last year at Biomm 96, I won an award in the Photomicrography category using a silverless process. The final print was a dye sublimation image produced from a high end scan back camera. It is an absolute a fact that these new cameras are very good and so the real motivation for purchase needs to be the type of product that is being produced. Simply the need to have a direct digital camera should not drive this type of a purchase. If this is the case, the Kodak DCS 210, a high end consumer camera is quite acceptable. In the end analysis, products need to drive the hardware needs. As consequence, one's entire computer operation needs to be integrated. As an example, which output device that will be available will influence the possible camera options. How the pictures will be incorporated into documents, at what resolution as well as how they will be stored all factor into the analysis.

Storage and Digital Files
One important factor in considering whether to acquire a digital camera revolves around image storage and retrieval issues. The storage and accessing of digital files continually is a concern for photographers. With 35mm 2 x 2 color slides, storage has always been achieved through the use of pages or storage cases with built in illuminators. More often though , the slides left the photographic department and went with the customer. Consequently few departments were overly concerned with storage beyond areas that were located in clinical areas such ophthalmology, pathology or dermatology. With the ability to create filmless images, the how to, the where to, and the who should store the files seems to be problematic and needs serious consideration.

Storage Media
It also is interesting to reflect for a minute on the evolution of storage media. High end digital cameras generate large files sometimes 5-to 25mB if not more. Consequently an integral part of the system needs to be the storage media the image will be archived on. Additionally the hard drive space in the computer itself needs to be a factored. Computers not so long ago were coming packaged with 40mB hard drives, while now a 2 -5 Gigibyte hard drive is common. Similarly storage media has also come full circle. One of the very popular original leaders in storage media was SyQuest® which was capable of saving up to 44mB per disk. With uncompressed 25 mB files, only one image could be archived on this type of disk. Compression of course is an important step that should be used. Remember the Bernoulli Drives®, like so many products from this very recent past, many have all but disappeared. Now Syquest sells 88 and 200mB drives. Many other products from the very recent past such as the magneto optical(mo) systems that stored 128 mB find themselves coming out with larger capacity storage abilities in the neighborhood of 650mB. An extremely popular new storage media is the Zip Drive which will hold 100mB while the Jaz drive will hold 1 gBs. The Zip drive which sells now for less than $100 is excellent for this purpose because of its very low price. Writable CD's are another very useful product for archiving and they will hold approximately 650mB. Storage devices are an important consideration because the archiving of these images takes up storage space. Producing 3 files that will be printed as 8 x 10's will require 60 - 70mB. If this activity were done three times a day for 5 days a week, the storage dilemma becomes quite obvious.

Before analyzing cameras, it need to be considered that the creation of the digital image can be achieved several ways. 35mm film can easily be scanned using any of the very good and moderately priced desktop scanners. In this fashion, quick, high res digital files typically in the 5 -6 mB range are produced for an investment of only $1,000. These files can be quickly be enhanced and utilized as necessary. Obviously using a scanner does not replace the need for the camera but can create a digital image. Also over the last few months many new intermediate quality cameras have been introduced that provide reasonable results. These type of applications might include but certainly not limited to head and shoulders portraits as well as quick press release work. The Kodak DCS 210 as well as the Fuji DS-300 are quite adequate for many of these applications. These cameras have found niche markets in the real estate business as well as in the insurance claims area. Their acceptance within the scientific community has been slow but I speculate that this is changing as I write.

The Professional Digital Cameras
The Digital Rev(s)olution is obviously here! The look of the pictures, the quality of the image resolution, and the capabilities of the computer to work on the images continues to mature exponentially. As a result, the serious photographer that has need for direct digital cameras will have countless choices and issues to weigh before making a decision. Cost, features, speed, studio or mobility and many other subtle operational issues will be part of the decision making. High end cameras can be categorized into 3 groups. The first group would include cameras that work like scanners and need to be driven by a computer. The second group of cameras would be instantaneous capture while the third group being multiple exposure instant capture. I have found that each group has advantages and disadvantages based on the type of work being produced.

Linear Array Cameras
Scanning cameras produce the highest resolution of the three groups. They work similarly to any film or flatbed scanner. The camera is composed of a single row of image sensors that form its CCD or charged couple device. The sensor moves across the image area from one side of the frame to the other. The CCD is moved by using a very fine stepping motor. There are many cameras that work like this such as the Dicomed Studio Pro, Phase One or the Leaf MicroLumina . Each of the backs is slightly different. Some fit into a 4 x 5 camera back similarl to the way a cut film holder works while others have a bayonet mount in the front that accepts a variety of lenses. The individual differences can easily be learned by referring to any distributor of digital products such as Logix or others. Since the camera is comprised of a single row of pixels over a fixed length(width), the camera is capable of very high resolution. The Leaf MicroLumina for example, has an array of 2700 pixels over a travel distance that would comprise 3400 pixel points(length) which produces an image of 9 million picture elements and a file of 26 mB. Additionally most of these cameras produce images that are a minimum of 36 bit depth. Unfortunately, Photoshop 4.0 still only acquires 24 bit images. As a result, some of the camera's high detail is lost even before it has ever been used.

Scanning cameras are typically slow in capturing images. As an example, when at a light microscope that would require a 1/15 second using Kodak 64T film, using a scanning type camera, the exposure might take 8 -10 minutes. Because the sensor is moving, this type of camera cannot record moving subjects. It also needs to be tethered to a computer. Computers with large hard drive space are required as well as a minimum of 32mB of Ram is also needed. One recent studio camera requires a machine with a minimum of 256mB of RAM. These cameras are low in sensitivity(response) and require high brightness to record them. The use of flash is also not possible because of duration while some tungsten filaments will experience flicker during the course of a long exposure. As a result, studios utilize HMI lights for this type camera because there is no flicker to create different exposures(brightnessess) as the sensor moves across the frame. The camera is solely a light sensor with the camera controls in the computer as a software interface. Often camera access can be found as a PhotoShop plug-in. Almost universally, these cameras have a pre-scan for initial set of the sensor based on the subject's requirements as well as the lighting. Image contrast can be adjusted, scan speed adjustments can be made as well as many other features such as color response are available. Some of the cameras allow fine focusing to be executed during the prescan by having NTSC out that is concurrent with the still digital signal. The image sensors also responds best to flat light. Ratios that would be similar for transparency film or less seem to be ideal for CCD's.

At the microscope, this type of camera provided exceptional results. Because these cameras do not use mirrors that would be associated with SLR type cameras, the image is less susceptible to vibration. Determining critical exposure was very important . With too much exposure, the sensor caused blooming or exposure was created in adjacent picture areas. This was evidenced as a color glow(exposure streaks) into adjacent shadow areas. As a result, making pre-scans that created a brightness value below 230 in the clearfield helped resolve this so long as the sample had adequate contrast. Flat subjects are really problematic regardless of capture media. With the scan speed determined, a white point could be set and the image corrected by the software. Another interesting discovery was that if the exposures were too short, the camera sensor often moved across the image field so quickly that vibration was introduced. Vibration in this type of camera is observed as bands or density differences across the width of the image. In the clearfield areas of a light microscope, this banding is very evident as density changes. At very low magnifications, where achieving Kohler is difficult regardless of image capture methods, the cameras produced obvious localized exposure differences as a result of the lamp filament. It was recorded as different pixel values as a result of the sensors being very responsive to localized brightness differences. The pixels really enhance edges naturally so through the use of 2 diffusion filters , the lack of uniformity in the background was removed.

Accurate color seemed initially challenging but very accessible. The sensors from different cameras, like slide films, have different color responses. It was interesting that the most accurate color was often achieved using lamps at approximately 3400 K at maximum light intensity. Through the use of neutral density filters to remove significant light, it could be speculated that the spectral responses of chip might be optimized at this color temperature. As it relates to brightness, it was also experienced that if a typical film exposure would be longer than 1/4 second with 100 speed film, these cameras did not operate.

Area Array cameras
The majority of cameras on the market seem to fall into two large areas, scanning and area array. Probably the largest group of cameras on the market are the area array type. Area array cameras see the entire image simultaneously as do film cameras. Consequently all the camera controls are the same on the digital camera that would be found on a film camera. These types of cameras are sold by many camera manufacturers such as Kodak, Nikon, Fuji, Canon and Minolta just to name a few that should be familiar names. So from the front, all the digital cameras look and operate the same as any film camera such as the Nikon N-90. Spot versus center weighted metering is but one of the many functions available as with any fim camera. Behind the lens is where the huge changes occur. Rather than a pressure plate for film, a Charged Couple Device is located there. As a detector, it has a vertical and horizontal pixel array as compared to film format. The physical dimensions of the chip determine its resolution. A small chip might be 640 x 460 pixels while the highest resolution chip on the market boasts a image resolution of 2K x 3K. Many intermediate resolution cameras have a chip approximately of 1K x 1.5K. Chips also have a sensitivity. Most cameras seem to exhibit sensitivities (ISO potential) of 80 at the low end to 1600 as the current most responsive. The sensitivity for most cameras can be changed or is considered variable based on lighting requirements. As the ISO is raised less quality is noticeable however even though proper exposure is achieved. The loss in quality is described as noise. Typically the higher the signal to noise ratio, the poorer the result. Conversely, when the ISO is lowered, the results are superior.

Because chips have a physical dimension, they often see less of the field than film cameras. As a result, required focal lengths are often not identical as with film recording. To be able to capture what a 50mm lens sees on the Nikon N-90S with film, the Kodak DCS 420mm uses a 20mm lens. As a very general rule of thumb, the chips require 1/2 the focal length of the normal lens when the camera where to be used with 35mm film. On a microscope, this often required using lower power objectives than one would first select. A field that can easily be observed with a 10X objective would now require a 4X for imaging if the requirements to record the same field of view were necessary.

The CCD as a device can only respond to differences in brightness not color. When using film, one can choose from many emulsions based on project requirements, however the CCD's must be modified to respond to color. As a consequence, color separation strategies are often required to create color vision. This is also true for scanning type detectors. One solution that is used is to place a Red, Green and Blue filter over the sensor in a linear fashion. A long red filter, a long green filter and a long blue filter sometimes 7µm in width, are run the length of the sensor. In this fashion, the surface area is divided into three equal spaces that each render a different spectrum. The computer software can then reprocess the signal and create a credible color display.

Specifically within the area array cameras, the solution to the color vision problems varies. The Kodak cameras for example have colored filters on each row of pixels. So across the row of 1500 pixels, there are 3 filter stripes for each row. Through the use of software interpolation, the image is written and color created from image processing. These cameras allow photographs to made anywhere at anytime using a variety of light sources as the cameras have shutter speeds and reasonable responses expected down to 1 second. I have found that below these times, the cameras often fail to respond accurately because the chip warms and fails. Sometimes the exposure is actually terminated. Another method to acquire color is through the use of mosaic techniques, where every four pixels in a square is outfitted with a different filters. Often the filters are R, G, B and with the fourth being either magenta or cyan or yellow.

Because the color is the result of software interpolation, there are sometimes digital artifacts produced. These color artifacts are often referred to as aliasing and are frequently observed in linear subjects that have high frequency patterns that span across several pixels. Aliasing is most evidenced in the medium resolution stripeing filter type cameras and is easily correctable in PhotoShop. The highest resolution camera on the market, the Kodak DCS 460 which uses this stripe technology does not display this problem. Using various options in PhotoShop 4.0, specifically in Image and Color controls, one can use commnads to change the radius and threshold of the pixel display all but eliminating the digital noise.

Another method that is used to create color is accomplished through the use of 3 CCD's. The image produced by the lens is broken apart by a prism and relayed through Red, Green and Blue filters to its own sensor. One camera that operates in this fashion is the Minolta RD-175. Each sensor is smaller than the chip as a whole, but the achieved results are quite acceptable. As a basic response, the chip of the Minolta camera has an ISO of 800 which was very important in when working in low light situations such as with darkfield, fluorescence and ophthalmic work.

Most CCD's are inherently sensitive to Infrared radiation. As a consequence, the use of a "hot filter" or IR cut off filter is desirable. The use of this filter is not a requirement, but certainly when using tungsten lights has great value. The high response of the chip to IR energy often causes an unusual color response. In the older Kodak publications, where Kodak IR film was discussed, a term referred to as false color was used. Through the use of CCD's, false color is also possible without the filter. Tiffen sells such a filter and it is referred to as a "hot filter".

The Fujix HC 2000 is a very interesting area array camera but is very different from other area array cameras. The Fujix 2000 is a studio area array camera with a NTSC video signal out. This feature allows for precise composition, focusing as well as exposure determination directly from another monitor which is required in addition to a computer work station. This camera created images with file sizes of around 5mB and was quite interesting for many reasons. It was excellent for use at the microscope as well as on a gross stand or portraits. The camera is tethered to a computer so it is not portable in the least. The camera required an ENG mount for adaptation onto a scope while any small video lens mount worked for studio applications. The ENG mount needed to par focalized to the eyepieces but this was not difficult to accomplish.

PCMCIA Cards
The images that are captured in most area array cameras are written to small removable hard drives sometimes referred to as film cards in the amateur market. These removable hard drives are also referred to as PCMCIA cards in professional circles and are available in variable storage capacities. Cards are classified by their physical size either Type 1, 2 or 3. Often the Type 3 card is the largest and has the largest storage capacity. Their storage capability has been continually growing since the introduction of these products. The Kodak DCS 460 often has been sold with at least a 230mB card. Referencing any supplier of such cameras, this type of information is readily available . It has been suggested as a rule of thumb that these cards sell for $100 per 5mB of storage.

Images are captured and then written to these miniature hard drives in this intermediate location for storage and retrieval. Once the camera's shutter has been activated, the hard drive of the camera also is activated. A term has evolved to describe this process as waking up the hard drive. Once activated, the camera can record the image and then write it to the drive. In most cameras, there is an LED or some other type of an indicator to reference that drive is writing. Some cameras are very responsive as to how long it takes to activate a system while others are quite slow. For this reason, shooting events that have the potential for pictures to be made at a moments notice such as in photojournalism, require the photographer to continually keep the camera awake(ready) so as not to miss any shots. Additionally, each camera has a different capability to hold several intermediates images before then writing to the drive. Each camera as a consequence will have a different burst rate or ability to record more than one image at anytime. The lower end cameras can only perform one activity at a time. Activate, capture, then write while the higher end cameras designed specifically for journalistic work, might be able to record up to 5 images before needing to write. Cards are removable from the camera and should never be removed while they are writing. The removal of a card during writing will permanently damage the card.

With the shooting completed, images from area array cameras will need to be moved from the camera/card to your workstation. This activity can be accomplished in several fashions. The camera itself can be tethered to the computer with a SCSI cable or the card can be ejected from the camera and the file accessed through the use of a card reader. A card reader is nothing more than a very small drive designed specifically for PCMCIA cards. These products vary in price and drives can be addressed through the PhotoShop Plug-in for that particular camera brand. Historically, each camera had its own file format which has been problematic. Formats such as DCS, HD, LDR MDR and others are a few of the many proprietary formats than have been problematic for users thus far. Recently though, manufacturers have been releasing cameras that save and export JPEG or TIFF image file formats which has greatly simplified working at various locations in the digital image chain

Conclusion
There are obviously countless cameras on the market, with each having their own distinct advantages and disadvantages based on applications. I have also worked with, but not extensively, with many cameras . It would be next to impossible to use all the cameras that are available as it would be for film cameras. This piece has been an attempt to lay out the many facets and details of selecting and using direct digital cameras.

As with as all new technologies, there will always be waves of acceptance and our field is clearly in a phase where the majority of photographers are, or will be "adopting"very soon . I have laid out many aspects of digital cameras for consideration as the move towards adoption is made. Digital cameras will continue to be produced more cheaply and deliver higher resolution for less money. As the differences in computer platforms continue to diminish, so do the large differences between the cameras for now. The digital camera market will never be totally stabile for long as new technology such as active pixel cmos begins to change the way chips are manufactured and integrated into cameras. The comment made some years ago by the JBC editor Joe Ogrodnick at a RIT symposium still holds much truth, "the only thing for certain that we can say about the future is that there will be change". The advantages for the use of digital cameras in certain applications is becoming quite evident. Certainly it is easy to project many without great challenge. Prior to purchase, adequate research is essential to evaluate the many options available. Additionally long term goals should be considered in setting a direction away from film with an integrated approach. Buying a digital camera will cause consumable expenses to go down, but the initial investment to get there will be high. Also the life expectancy of such an investment is a factor. Remember when the purchase of a Nikon F -3 would last for 10 years? Well the acquisition of a digital camera and computer system will never achieve that life expectancy. Welcome to the time of rapid change.

Idiotic Mistakes to Avoid When Learning Digital SLR Photography

1. Idiotic Mistake:
You accidentally delete you files from your camera memory card before you have transferred the files to a computer or disk. Then you go right on using that same memory card to take other pictures! Which means you lose your chance of recovering your deleted files. The files on a memory card are recoverable. But once you have overwritten them with new files, recovery becomes impossible.

What You Should Do:
Always carry extra memory cards with you. If you do accidentally delete your pictures, separate out the card with the deleted files and don't use it. Then find a good file undelete program (which you can find online) and recover your lost files. In many case you will be able to get them back. But only if you haven't overwritten them. After you have succeeded at your data recovery, you can use your memory card again.

2. Idiotic Mistake:
You go on vacation and leave your battery charger on the other side of the world. When you are just seconds away from taking your best yet photograph, your batteries run out and you have to use your mom's 5 megapixel Canon Prosumer Camera instead of your own Canon Digital Rebel SLR.

What You Should Do:
Don't assume "well, I moved everything over from my camera bag to my backpack, so it should all be in there." As ridiculous as it might sound, make a checklist of what photography equipment you need to bring with you. At least use it when you are traveling far away. Check your checklist when you pack and make sure you have everything.
I know a girl who violated rule point 1 above, and wound up returning to the mountains of a foreign country to re-shoot the lost photographs. Now I won't tell you who this girl is. It would embarrass her. But suffice it to say that she is a girl who most people think of as being very smart. If it happened to her, it can happen to you too, so I hope you benefit from this advice.

I know a girl who violated point 2 above, and wound up having to take portrait photographs of her family, with a point-and-shoot mounted on a tripod. While her Digital SLR rested in its bag, uncharged, she cringed at the discolored shots (due to no white-balance control), difficult focus, unchangeable aperture, and fickle exposure. All because she left her charger in another continent.

Finding the Right Digital Camera

Finding the Right Digital Camera
The overall goal of the Imaging Resource website (www.imaging-resource.com) is to help people chose and use digital imaging technology as effectively as possible. As simple as they are to use, choosing the right digital camera involves a number of decisions. Key issues are computing platform, image quality, onboard image capacity, exposure versatility, feature set, and included software. In this article, we'll lead you step-by-step through some of the issues to consider in making a purchase decision, and at the same time, suggest some things to look for in the test images we've collected on our website.

We're interested in your feedback and experience! We invite you to elaborate on this article by leaving comments via the database link at the bottom of the page. You can also give feedback in our "Forum" discussion-group section.

Computing Platform
This is an obvious consideration but it is fast becoming less of an issue than it once was. Most current cameras can be interfaced with both Mac and Windows platforms, although some include more software for one platform than the other, and a few work on only one platform. (If a camera only works on only one platform, it's more likely to be Windows.)

Image Quality
Image quality is a complex subject that includes exposure accuracy, color purity, optics, and image compression techniques. We'll cover this whole area in greater detail later. For now, the important thing to remember is that there's really no substitute for direct experience. Look at the sample images on the Imaging Resource Comparometer (TM) website (http://www.imaging-resource.com/IMCOMP/COMPS01.HTM), paying particular attention to images that represent your expected usage. You may be surprised by the differences between cameras!

Onboard Image Capacity
Depending on your application, the amount of onboard image storage could be pretty important. There is generally a tradeoff between image capacity and image quality, so don't get too excited about high image capacity until you compare the amount of storage in relation to image resolution. One camera may promise to store twice as many images as a competing model, yet have no more actual storage space. The consequence would likely be a loss of image quality. Onboard camera memory may range from 2 to 8MB, while image storage capacity can vary from 10 to 100+ images.

Reusable Memory Cards
Many cameras allow you to make your own decision about the memory/cost tradeoff by allowing you to store images on plug-in cards. This approach allows users to add as much or as little memory to the camera as they feel they need. Once upon a time, most cameras used a single type of memory card (the so-called linear PCMCIA), but those days are long past. Today, there's a plethora of memory types in use, although the market seems to be settling down to a choice of either CompactFlash or SmartMedia. (Look for an article on removable memory to appear soon on the Imaging Resource website.)

Exposure Versatility
One notable disadvantage of digital cameras is their inability to handle radically different lighting conditions. With film cameras, you can compensate for different lighting situations by using different types of film. With a digital camera, the camera's image sensor acts as the film, and it is not interchangeable. So you'll want to be sure that the camera's exposure system (shutter speed, variable lens opening, supplementary flash, etc.) has enough flexibility to handle a wide range of shooting conditions.

The first step in evaluating a digicam's exposure system is to look at its "equivalent ISO number," which is a measure of how sensitive the camera's sensor is to light. A higher number means the camera can successfully capture images with less light. Most digital point-and-shoot (DPS) cameras have equivalent ISO ratings in the 80-200 range, although some go well beyond these limits. In addition to the ISO rating, look for a wide range of shutter speeds and lens apertures. Typical numbers for shutter speeds are from 1/1,000 to 1/30 second, and for lens openings from f/2.8 to f/16. (Although the present generation of cameras has shutter speeds ranging from 1/2 to 1/10,000 of a second!) The wider the range spanned by these two sets of numbers the better.

Flash Capability
Also look for the availability and capabilities of a built-in flash. Key factors here are the range over which the flash will be useful, and the number of "modes" it has. First-generation digital cameras had fairly limited flash power, evidenced by maximum working distances of 10 feet or less, but many current models now reach 16 feet or more. Flash modes refer to different ways the camera's light sensors can control the flash circuitry. In the most basic mode, the camera "stops down" (closes) its lens aperture and runs the flash at full power, so most of the light hitting the subject is provided by the flash. Some cameras offer a "fill" mode for their flashes. In this mode, the camera sets the shutter speed and lens opening based on the amount of light coming from the scene overall. In "fill" mode, only enough flash illumination is used to "fill in" the shadows and bring the illumination up to the minimum required. The result is often a more natural, evenly lit subject. Many cameras also offer special "red-eye reduction" flash modes, in which the flash blinks one or more times before the actual exposure, to reduce the size of the subjects' pupils and minimize the internal reflection that produces red-eye.

The Feature Set
Besides the basic parameters listed above, you'll find a variety of features on the cameras that may have varying degrees of usefulness in your application.

Camera Lens
Many DPS cameras have a "fixed-focus" lens, in which the focal point is set so that everything from about 4 feet out is in focus. This is handy if you need to photograph subjects in that range, but pretty useless if you have to take a picture of something only a few inches wide. Some DPS units have optional attachments to improve their close-up performance, while others offer special "macro" focusing modes that let you get much closer to the subject than a standard lens would. (Look at the macro test shots on the Comparometer (TM) site to find out how well various cameras do in this regard.)

Wide-angle photography is another important capability. It can be particularly useful for indoor family activities, where shooting conditions may be cramped, or for real estate or insurance photography. Again, some cameras have aftermarket accessories available to expand their field of view, so you will want to take this into account when making your purchase decision.

Many digital cameras feature zoom lenses, with a range of focal lengths running from a mild wide-angle (roughly equivalent to a 35mm lens on a 35mm camera) to a mild telephoto (slightly more than the equivalent of a 100mm lens on a 35mm camera). While you invariably pay more for a camera with zoom capability, we've found the feature very useful in real-life shooting situations, and well worth the investment.

Self-Timer
A self-timer is simply a shutter delay that allows you to trigger the camera, then run around to be included in the picture before the shutter snaps. It can also help reduce camera shake when the camera is mounted on a tripod or other solid surface. Pressing the shutter button causes a certain degree of vibration, and using the self-timer gives the camera enough time to stop vibrating before the shutter is released. This feature is an easy addition from the standpoint of the technology required, but often omitted. If you plan to be part of any group photos, or plan to take a lot of low-light scenes, see that your camera has this feature!

Battery Life
You'll find a wide variation between cameras in how long their batteries last. Unfortunately, it's difficult to consistently measure power drain for DPS cameras, though Imaging Resource does report power usage in various operating modes as part of its digital camera reviews. Some manufacturers specify expected battery life and others don't, but you should be wary of manufacturers claims for battery life, as they are sometimes overstated, or may be specified with costly battery types (such as lithium cells).

Another important question to ask about a potential digicam purchase is whether the camera can run off rechargeable batteries. If you plan to take a lot of pictures, the ability to use rechargeable cells could save a lot of money in the long run. (Note that the mere presence of an external power adapter may not mean the camera can use rechargeables, and probably does not mean the unit will recharge batteries while it is plugged in.)

External "booster" battery packs are available for some cameras, increasing their working time in the field many fold. Keep this in mind if you plan to spend long periods on the road, far from power outlets. If a "booster" pack isn't offered, make sure you change or replace batteries in the field.

External Power Adapter
While we're talking about power, how about an external power adapter? You'll find DPS cameras generally consume much more power while communicating with the computer via their serial ports. If you have an option to run from a power adapter while downloading images, your batteries will last a lot longer. It's important to note here though, to be certain to use the correct power adapter with you camera, as the wrong one could easily fry a $1,000 investment!

Included Software
The software included with a camera can be pretty important. In fact, this is an area where you'll find some of the greatest variation between cameras. In the Imaging Resource digicam reviews, we try to give readers some idea of how the different units fare in this respect. Here is an overview of the most critical software needs:

Image Download
One of the most important functions to consider when reviewing digital camera software is how convenient it is to unload images from the camera. Can an entire camera-full of images be pulled onto your hard drive quickly for later processing? Or, is the camera held captive while each image is individually processed? Alternatively, can "thumbnail" images be viewed prior to downloading the full-size files? This can save a lot of time in culling the few best shots from a large group.

Image Manipulation
Getting the images into the computer is just the beginning. Does the included software allow you to manipulate the images after you've captured them? How easily can you compensate for poor exposures, color casts, or misaligned images? How about minor retouching to remove blemishes, errant reflections, or red-eyes? Most digital camera packaging includes a list of accompanying software, or you can find the information within the Imaging Resource reviews or on the camera manufacturer's website. We suggest you review the capabilities of the software so you know exactly what you'll be able to do with your images once you have them on your computer.

File Formats
File format is the form in which your images are stored in the camera's internal or external memory. Standard still image formats include uncompressed TIFF and compressed JPEG files in RGB (red-green-blue) color mode, plus a number of other formats, such as GIF, EXIF, and MPEG (for movies). File format is critical to the software's file-export capability, and to your intended usage. Your requirements may be different if you plan to capture images for multimedia presentations rather than printed output. Most camera software is fairly competent in providing images in the standard file formats, with some manufacturers increasing their present levels of capability. Virtually all packages provide for export of RGB TIFF or JPEG files, which are supported by most document layout and word-processing applications, but if you need formats beyond the standard TIFF or JPEG formats, you'll have to look into what the camera software supports more carefully.

Cataloging
One of the first things you'll learn once you start using a digital camera is how fast images pile up! (If you haven't already, you'll doubtless find yourself buying a much larger hard drive.) Having adequate storage space is only half the battle though; finding images is another matter entirely! In recognition of this fact, some cameras include at least rudimentary image cataloging capability in their software packages. On the Mac, just the ability to create a "thumbnail" preview to display as the file icon is a big plus. (A word of warning: Hundreds of file icons with thumbnail images attached can really slow down access to folders on your hard drive. Turning off the "preview" option and using a cataloging program instead can really help system performance.)

Some manufacturer-supplied camera software includes rudimentary cataloging capability, but in our experience, none of these packages offer the level of capability you'd need to manage more than a few dozen files. Accordingly, if you need to track large numbers of images, you should really look at one of the many image database programs on the market. Some manufacturers have begun to bundle more powerful third-party image cataloging products with their cameras -- a very welcome addition.

Links to External Applications
One of the nicest characteristics of "desktop" applications is how easily you can move data or design elements from one application to another. The Macintosh has excelled in this respect for years, and the Windows platform made rapid strides beginning with Windows 95. There are varying degrees of integration available, however. Some software requires you to save a file to disk in one application before it can be imported into another. Other packages let you place an element from one application directly into a document of another. Sometimes, you can simply "drag and drop" an image from the camera software into a page layout program. Look at the camera software with your specific application in mind, and see what's required to move the images from the camera to the programs where you'll ultimately be using them.

Image Quality
Image quality is one of the most important characteristics to consider in choosing a camera, and is impossible to evaluate from manufacturers' spec sheets. Ultimately, the only way to tell if a given camera will produce acceptable results in your intended application is to compare photos taken by various cameras of similar subjects, and to test them in each of the shooting conditions you expect to encounter. (This underscores the importance of the test images provided on the Imaging Resource website: http://www.imaging-resource.com/IMCOMP/COMPS01.HTM.)

The reason image quality is so hard to get a handle on is twofold. First, there is currently no standard, objective scale by which to measure color accuracy in digital cameras. Second, all DPS devices use image compression technology to cram images into their limited memory. Depending on the algorithm used and the amount of compression applied, image quality can vary widely, even between devices using the same CCD sensor! So, let's look at some of the elements that contribute to image quality:

Color quality
Color quality is a complex and generally misunderstood topic. While it is probably less an issue for typical point-and-shoot applications than for high-end studio cameras, the large differences we've found between cameras suggests that a detailed discussion of color quality would be useful to any consumer who is investigating digital cameras.

Color quality is actually made up of two related, but different, parameters -- color purity and tonal balance. People tend to assume color errors can be corrected easily in an image-editing program such as Photoshop, and therefore tend to discount their importance. This is generally true of tonal errors, but errors due to color purity are virtually impossible to fix.

Gray Balance & Color Accuracy (Tonal Errors)
As mentioned above, tonal errors are fairly easily compensated for in a digital image, often with very gratifying results. Of these, gray balance is both the most dramatic and the most easily corrected. While a full treatment of gray balance is beyond this particular discussion, we can nonetheless cover a few key points, and see the effect that relatively simple adjustments can have on an image.

As the name suggests, gray balance refers to bringing gray tones in an image into neutral color balance. This is done by balancing the individual red, green, and blue channels across the entire tonal range. Of course, if the digital camera's blue channel responds more than the red or green channels, the pictures would have an overall blue cast. While gray-balance problems are sometimes as simple as this, generally they are more complex.

When reviewing the color accuracy of a digital camera, it is important to pay attention to the colors across the entire range of tonality, which means you must look at gray balance in the shadows, the highlights and all points in between. In practice, it is neither practical nor necessary to make gray-balance adjustments at each step across the whole tonal range. Usually, adjusting the balance in the highlights, shadows, and midtones brings dramatic results with relatively little effort.

In Photoshop, these adjustments can be made with the Image/ Adjust/ Levels function, and correction curves can be saved for fairly automated application to groups of images captured with similar lighting. The color charts above and at right show sample results. The image above is "as captured" by one of the cameras we've tested. The image on the right is derived from the same file, but has had a rudimentary gray-balance adjustment performed on it. Note how much "cleaner" and brighter the colors are, almost as if a layer of grime had been wiped from the image.

While gray-balance adjustments can produce a dramatic improvement in color quality, they are by no means a panacea. Proper gray balance can substantially brighten colors, but it will not correct color impurities resulting from poor-quality color filters. You also need to keep in mind that time spent adjusting gray balance is time lost to more productive work. A camera that looks like a bargain may prove otherwise if you have to spend 20 minutes color-correcting every image it produces.

Evaluating Color Purity & Accuracy
Important as it is, color accuracy is a slippery parameter to quantify. Rather than trying for some sort of absolute standard for color accuracy (which would likely be difficult to interpret anyway), Imaging Resource has opted to provide consistently exposed test images that would help you make your own subjective evaluations. The "Dave Box" target includes a Macbeth color chart, which is a well-established and reasonably consistent color reference that is readily available at most camera stores.

Dynamic Range
Dynamic range measures how wide a range of subject luminance (e.g., brightness) a sensor can accurately reproduce. Most digital cameras can capture a wider range of brightness values than the printed page can reproduce. The key issue is how good a job the hardware and software does of compressing the full range of scene brightness into a range that output devices can reproduce. This capability, whether in a camera or a high-end scanner, is called tonal compression, and it is an important characteristic of high-quality input devices.

Tonal compression is as much an art as a science, and different devices use different input-to-output curves to accomplish it. Generally, you want to avoid losing either the highlights or the shadows, yet still maintain reasonable contrast in the midtones. Visually, photographers are accustomed to looking for tonal problems in very light and very dark subjects. Traditionally, people shoot white porcelain objects to study subtle highlight detail and dark camera bodies or electronic equipment to look at shadow detail. This is a valid approach, but subtle differences are often difficult to detect on the final printed output. On screen, without an assist from Photoshop or some other image-editing program, the problem is even greater. Especially in the shadow areas, the tonal response of CRTs is very poor.

The way to really see what's going on is to use the Photoshop Levels control (or the brightness/contrast adjustments in consumer-grade imaging programs) to stretch the tonal range of the image in the areas you're interested in. For highlights, this is accomplished by moving the black-point slider well up into the midtones. This forces everything darker than the midtones on down to black, stretching the remaining tones over a wider range and emphasizing tonal differences in the brighter portions of the image. For shadow areas, reverse the procedure, moving the white-point slider down into the midtones. This forces everything from the midtones on up to white to go all the way to white, stretching the shadow tones across the full range and emphasizing subtle tonal differences there as well.

The pictures below show this process applied to an image with deep shadow detail. In the first we see the original image, and the display from a Photoshop Levels adjustment window. Note that all of the image data is clumped on the far left, in the deep shadow. In the image itself, there's no apparent detail to be seen. In the next frame, we've moved the highlight slider far to the left until it's just touching the right-hand edge of the histogram "lump." See how this brightens the screen display, pulling up detail where none was to be seen. Finally, the last panel shows how the brightness levels of the image have been "stretched" to cover the full tonal range. The image is the same as in the middle panel; the change has just been made permanent in the file. Note that if the gray balance of the camera was inaccurate, these procedures would also show color casts in either the highlights or the shadows that wouldn't be obvious to the unaided eye. (In other words, don't be surprised if your shadows end up looking yellow or red after you've tinkered with them to this extent.)

Finding "hidden" images in deep shadows

The starting point: There's a range of tone there, but all clumped at the extreme shadow end of the range.
By moving the "highlight" slider down to lightest tone on the graph, we see the hiddin detail.
When the operation is complete, the available brightness values are spread across the full range of the display.

What do you look for in evaluating a camera's tonal range? Whether in the highlights or shadows, you want a camera to reproduce tonal variations smoothly, without obvious "tonal breaks," "posterizing," or "quantization" (three different terms all meaning the same thing). The most common defects occur when highlights wash out to white or shadows plug up, going black in regions where there is still some tonal variation in the subject that you'd like to retain. These faults are sometimes hard to see, but Photoshop will smoke them out every time.

For the DPS cameras, the "deep shadow" test of charcoal briquettes in a black box was almost too severe a challenge. Most of the devices we've tested could only just barely discern the presence of the briquettes, let alone show any significant detail. Nonetheless, you'll find clear differences in performance if you play with the camera files in an image-manipulation program.

Camera Limitations
In discussing techniques for finding camera limitations that aren't visible to the naked eye, a natural question is, "Who cares?" After all, if you can't see it, why worry? The answer is that sooner or later, you'll need to "push" an image in some way, perhaps to open up the shadows, boost midtone contrast, or hold back the highlights a little. When you do this, any tonal imperfections will be magnified, along with whatever detail you're trying to bring out. If you've never shot a photo that wasn't perfectly exposed, then congratulations, and just skip this entire section. If you're subject to the same slings and arrows as the rest of us mortals, though, you owe it to yourself to look carefully at what a digital camera will do before you invest your hard-earned money.

Sensor Noise


The characteristic that most limits the overall tonal range of a digital camera is noise in the sensor array. Without getting overly technical, a noisy sensor means you'll see "grain" or "snow" in solid grays or colors. This effect is particularly pronounced in shadow areas. If you download and play with images from the Imaging Resource site, you can use the procedure described earlier to boost the shadows into an easily visible range. The darker steps of the Kodak gray scale will give you the most consistent reference to work with, but for subjective evaluation, the charcoal briquettes in the black box are perhaps the most useful. Sensor noise usually appears as "snow" in the image, much as you would see on a television set experiencing poor reception. Depending on the construction of the camera system, the noise may appear as randomly distributed monochrome or colored flecks. (Certain sensor irregularities may result in some patterning to the noise flecks, but usually the distribution will be fairly random.)

If you performed the earlier experiment, you're likely to have had a good look at sensor noise while looking at shadow detail. In the process of pulling the shadow tones up into the visible range, you would have also greatly increased the visible effect of any sensor noise that might have been present. The illustration below shows a shadow detail sample from a studio camera with high noise and a marked color cast in the deep shadows. In DPS cameras, noise effects are largely masked by the JPEG image-compression process. Noise is nonetheless a primary limitation, even if we don't see the effects directly.

Sensor & Optical Artifacts
As we discussed earlier, each image captured by a digital camera is actually three separate images (red, green, and blue). In order for your picture to look right, all three of these images must be kept in perfect registration. If the registration between the tricolor images is off at any point, the result will be a color "artifact." (Artifact here is just another word for something in the image that came from the camera, rather than from the scene.) In practice, most DPS cameras use "striped arrays," so the color registration is both fixed, and inherently offset. This gives rise to a particular type of color artifact.

Striped Sensor Arrays

Ideally, a digital camera would arrange to have separate red-, green- and blue-sensitive sensor elements staring at each pixel-size area of the scene. In most cases, this is prohibitively expensive, even for high-end studio cameras. A popular, low-cost way of approximating this capability in a digital camera is to "stripe" the sensor array with microscopic color filters. The result, as shown here, is generally an array of RGB color triplets, much as you can see if you look closely at a color TV picture tube (or computer display CRT) when it is operating. This approach trades off resolution for single-shot capture capability, but carries with it other penalties as well.

Array Striping Artifacts

The most significant limitation of striped sensor arrays is that they are prone to generating color moirés and other artifacts when viewing small, high-contrast objects. (This situation frequently arises in product photography, where fine black type on labels can cause problems.) In the Davebox images posted on the Imaging Resource website, you may be able to see such artifacts around type, or as a colored moiré on the resolution target with the repeating patterns of vertical lines. In print applications, as long as the file isn't magnified too much, these artifacts are somewhat hidden by the half-tone printing process. If the image is magnified at all, though, these artifacts can be quite evident. In multimedia applications, these effects are almost always visible.

In the resolution test images appearing on the Imaging Resource website, you'll find several places where closely spaced parallel black-and-white lines produce color artifacts when photographed by various cameras. These false colors are caused by an interference pattern between the spacing of the lines in the test target and the spacing of the red-green-blue filters on the surface of each camera's imaging array. Differences in compression techniques and optical systems between cameras make them more or less prone to producing such artifacts. While this pattern represents a particularly severe test, a camera that has trouble with it is also likely to have problems with things like venetian blinds, etc.

Overexposure "Blooming"
A final limitation of CCD sensors is their reaction to severe illumination
overloads. This is the reason for including a shiny pot lid in the Dave Box targets on the Imaging Resource website, because it reflects light sources back into the camera lens. In the face of extremely high light overloads, some CCDs will "leak" charge from the overexposed elements into adjacent cells. This phenomenon is called blooming, and various methods are employed to prevent it. It most frequently shows itself as a colored fringe around specular (shiny) highlights. Frequently, the sensor will bloom differently in each of the red, green or blue channels, producing the colored fringes where one channel has bloomed more than the others. The impact of this for your particular work will depend on its nature. If you intend to photograph a lot of chromed auto parts, blooming could be a big problem. On the other hand, it would be a complete non-issue in photos of bath towels.

Resolution(!)

Resolution is one of the most misunderstood, misrepresented, and confusing parameters in the entire field of digital photography. It is also one of the hardest characteristics to specify in a precise, objective manner, particularly for the digital point-and-shoot cameras. One of the most important things to understand about resolution in digital cameras is that pixels are not resolution! ALL of the entry level point-and-shoot cameras use large amounts of image compression to squeeze a reasonable number of images into their limited memory. The complexity and variety of these compression schemes makes it nearly impossible to arrive at any meaningful correlation of pixel count with the camera's ability to resolve detail. Once again, it's really important to look at test images to determine how each camera actually performs.

It was to resolve just this conundrum that the "WG-18" resolution test target was developed by an international committee of imaging scientists. It contains a multitude of test patterns designed to reveal exactly how well a given camera can resolve fine detail. A full treatment of the target is well beyond the scope of this article, but even the uninitiated can look at images of it taken with two different cameras and rapidly ascertain how well or how poorly they perform in relation to each other. As always, let your own eyes be the judge, and use the Comparometer™ to perform your own side-by-side comparisons.

Image Compression
At first glance image compression looks like magic. In fact, at second glance, it's pretty easy to convince yourself it is magic! How else would you describe a technology that can cram sixteen 1MB (megabyte) images into a single megabyte of storage space? Of course, nothing comes for free, not even with the spiffiest of high technology. So, while you can get away with pretty substantial amounts of image compression without people noticing, the level used in many DPS cameras is well beyond that point, and different devices succeed to varying degrees, depending on the details of their particular compression techniques. (Although, as memory has become cheaper, manufacturers are finding it to their advantage to trade more memory usage for less compression and therefore better picture quality.)

The key to usable image compression is to throw away "unimportant" information in the images, and to take advantage of local areas of similarity within each image. For instance, you don't need 24 bits of information to tell you what color a particular piece of an image is, if it happens to be about the same as the pieces on either side of it: Just record the differences! If the differences are small, the information you'll need to store will be small as well. Also, the eye tends to be much more sensitive to certain kinds of detail in an image than to others. If we can find a way to throw out only the detail our eyes aren't very sensitive to, we can reduce the size of the file without our eyes noticing what we've done.

This is the essence of all image compression schemes, but as you may suspect, the concept is easier to describe than to implement. While standard techniques exist, there is a lot of latitude as to how manufacturers can tweak them to produce the best results for their particular camera. Recent advances in compression technology go beyond standard techniques, and some manufacturers have taken advantage of them to capture finer detail with little increase in memory usage.

When looking at sample images on the Imaging Resource website, the effects of image compression generally can be seen as a "blockiness" in areas of fine detail and high contrast. Look around the edges of objects that contrast strongly with their backgrounds. You'll see errors introduced by the compression process in the form of square blotches at the corners, and "stairstepping" down diagonal edges. Note too, that it is important to look at areas with much "flatter" contrast as well. Sometimes, manufacturers tweak the compression methods in ways that throw out too much information in areas with subtle contrast differences. These cameras tend to lose the shading and reduce even toned areas to blocky chunks of flat color.

Digital Point & Shoots: Today into Tomorrow
Digital point-and-shoot cameras have made dramatic strides in a very short period. Since early 1998, the higher-end units have been rapidly approaching parity in image quality with conventional film-based point-and-shoot cameras. As this trend continues, the day of "filmless" photography will truly arrive.

Article by Dave Etchells

Thank you very much for very useful tips!

Top 7 Digital Camera Accessories and ExtrasFrom Michael Carr,

Your Guide to Digital Cameras.

FREE Newsletter. Sign Up Now!Now that you have a great digital camera, you can enhance or improve the experience with many different digital camera accessories. Some (such as a decent camera bag to protect your investment or extra memory cards) are crucial, some (like a good photo printer or tripod) are simply handy. Here is a list of the best digital camera accessories that should be the next on your to-buy list once you get a camera.

1. Camera Bag

It is important to protect your digital point-and-shoot camera from LCD scratches, dings and other general abuse. A great camera bag can do that. You don't want one that is too big and bulky, but you also need to be sure your camera fits. They can hold all the little extras, too, like batteries and memory cards. Here is a list of the top camera bags for digital point-and-shoot cameras. If you use a SLR, instead see my list of Top Digital SLR Camera Bags.

Top Picks: Top Camera Bags for Point-and-Shoot Cameras

2. Memory Cards

Even if your digital camera has some built-in memory, you can be sure this is one of the first investments you will have to make. Don't believe me? Go shoot a handful of photos, and then see your space for images dwindle to nothing. Ouch! Having another large-capacity card, or even a couple medium-capacity cards, is truly manadatory to enjoy your digital camera.

Top Picks: Top High Speed, High Capacity Memory Cards

3. Camera Tripod

Tripods really are a necessity if you’re serious about photography, and that’s that. I know they’re big, bulky and a pain to carry around, but if you want to get rid of that camera shake that seems to appear in every one of your photos, then it's time to start the hunt for a good tripod. Get more tips on choosing the right tripod.

Top Picks: Top Mini Portable Tripods

4. Photo Printer

If you have a digital camera, a great photo printer will eliminate the middle man when it comes to getting wonderful photo prints for albums, to share with families or to frame and display. You want to be sure to choose a printer that is suited for photo printing, and will produce dazzling print-outs. If you prefer to print on the go, see my list of Top Compact Photo Printers.

Top Picks: Top 5 Photo Printers for Making Your Own Digital Camera Prints

5. Photo Storage Device

If you plan to shoot a lot of photos, especially while on the road traveling, save yourself the nuisance of lugging along your laptop or spending a load of money on multiple memory cards. This storage device accepts 7 memory card types, and stores up to 100 GB of images.

Top Picks: Top Photo Storage Devices

6. Photo Editing Software

Even though many cameras come with photo software of some sort, you will probably find you want to upgrade to another more advanced program. The great thing about digital photography is you can fix those little problems later. A good software photo editing program is key to that.

More: Compare Prices

7. Digital Picture Frame

Why get a simple do-nothing picture frame when you can have an amazing electronic version that displays slide shows, or even receives photos from family and friends across the country?

Top Picks: Top Digital Picture Frames

Credit: Camera.About

My Favorite Digital Photo Tips

All about memory card formats, photo sensors, and more.

Steve Bass

My recent trip to the Galapagos was filled with close-ups of sea lions, giant tortoises, Galapagos Mockingbirds, and Red Footed Boobies. Last week I talked about the digital camera I used on that trip, the Nikon D100. This week I want to talk about memory cards and point you to a few articles and newsletters that'll help you deal with the holiday pix you've got on your hard drive.

Behind the Scenes

Good digital cameras need high-end digital film, or memory cards. I always thought all memory cards were the same. Nope. To accompany the Nikon loaner, Lexar slipped two 512MB Professional CompactFlash cards into my camera bag. The memory cards have , Write Acceleration, which is firmware embedded in both the camera and the memory card that speeds up the way images are written to the card.

So far, Nikon, Sanyo, and Kodak Professional cameras make use of the technology. The speed of these puppies is rated at 24X, which is about 20 percent faster than standard memory cards. They aren't cheap: They run about $370 each, compared to about $270 for 512MB cards rated at 12X. A minor concession to the high price is that Lexar throws in a handy USB CompactFlash card reader.

Dig This: Want a time killer filled with art and music? Check out Virtual Om. My favorite? The Spinners, bottom row, fifth from the right.

Clearing Up Some Digital Confusion

If you're confused about the various memory storage devices available for your camera (and which can be shared with, say, your MP3 player), you'll want to read "Mobile Computing Tips: Flash Memory and Small Storage." It provides a quick explanation of the six most commonly seen memory devices.

If you don't have time to read that newsletter, you can review a handy comparison chart from our "Mighty Mni Media" story. And for another view of CompactFlash speeds and storage capacities, check out the Digital Film Comparison Page. [Thanks, John L.]

More Confusion: The Photo Sensor

You may not know it, but a digital camera's sensor plays a key role in taking sharp and true-color pictures. In "Mixed Verdict on Photo Sensor," Grace Aquino, along with our PC World lab experts, explains the difference between CMOS (complementary metal-oxide semiconductor) and CCD (charge-coupled device) sensors; they also compare these sensors to something new, a Foveon X3 sensor. The story's worth reading if you're going to buy a camera in the next six months or so.

Before and After You Start Shooting

I've mentioned Dave Johnson's Digital Focus before, and I'll do so again: This newsletter is loaded with top-notch advice for shooting digital images. For instance, I'm going skiing next month. It's inevitable that I'll take awful shots filled with a bright sky and snow, leaving absolutely everything else underexposed. Have you ever had that problem? (Don't send me samples, thanks.) Dave has a good solution in "Digital Focus: Take Great Winter Photos."

Lighting in unique settings has always been a stumbling block for me. I end up over- or underexposing the shots and having to fix them later. Taking the shot right the first time would help. "Digital Focus: Tricks for Tricky Lighting" has more than a few guidelines for doing just that.

If you're ever wanted to create a contact sheet of your digital photos, you know how difficult it is to do. But there's an answer in "Printing a Contact Sheet."

One technique I've been using is creating panoramic views from multiple photos. It's not hard to do; Dave takes you through the steps (and recommends some software to do it) in "Digital Focus: Make a Panoramic Photo."

credit: cameras.about