How Cameras Work

Kinds of Photography

Great Photographers

Digital Camera Advantages

Features to Look For

More Features to Look For

Professional Cameras

Accessories and Summary

Camera Care

Useful URLs

Annotated Bibliography


More Features to Look For


Most digital cameras have an on-camera "histogram" display. The histogram is a little graph that shows brightnesses along its horizontal axis and the number of pixels in each brightness zone along its vertical axis. Here's an example:

What this particular histogram tells me is that most of the scene is in the darker ranges and some of the darkest parts have been lost completely. I can tell that the darkest parts have been lost because the pixels at the left side are slammed up against the edge of the histogram. If I saw this histogram on my camera I'd increase the exposure and shoot again. If I were in automatic mode I'd use exposure compensation and step up the exposure by about one stop. I also could switch to full manual mode and either increase the aperture by one stop or cut the shutter speed in half.

The ideal exposure would leave at least a tiny space at the left before the darkest part of the histogram display starts and a tiny space at the right after the brightest part ends. If the whole scene is in that range I can make any necessary final adjustments on my computer before I print. But in the picture represented by the histogram above there's detail beyond the edge on the left side that I'll never be able to get back.

What you're more likely to see is the reverse of the histogram above – with the brights slammed up against the right side of the histogram. When it comes to measuring exposure, ISO isn't the whole story. Two other things that enter in are the response curve over the range of brightnesses and the ability of the recording device to handle the whole range of brightnesses in the scene. Photographers call the ability of the recording device to cover a brightness range "latitude." Fast film usually has greater latitude than slow film.

CCD and CMOS sensors have a response curve that compresses low light levels more than high light levels. To make a long story short, what that means is that you may be better off slightly underexposing digital shots than overexposing them. I emphasize "slightly," and in the spirit of full disclosure, have to add that that's an oversimplification of a complicated subject. The reverse is true with film. If you underexpose film the shadow details will be gone forever. If you slightly underexpose a digital picture you usually can pull the shadow details up to an acceptable level because the details are still there even though they're packed together at the low end. If you overexpose film you usually can recover detail in the highlights by "burning" them in on an enlarger. With digital, if you overexpose much, the highlight details will be gone forever.

In the spirit of full disclosure I also need to mention "ETTR": expose to the right -- the philosophy in digital photography that says you need to expose so that the brightest parts of the picture are just below "blowout," in other words loss of all detail. ETTR goes back to the fact that the majority of the data in a digital capture is in the brightest parts. I practice ETTR whenever possible. It gives me the most data when I work in Photoshop.

Having a histogram display on your camera can save you heartbreak when you go to print and discover that the details you wanted in your picture are gone.


Digital cameras store their images on a " flash memory" card. Flash memory comes in several flavors. The most common variety nowadays is "secure digital" (SD), though most professional cameras use "compact flash." Sony has its own variety of flash memory called a "Memory Stick." Olympus sometimes uses a version called "Smart Media," a name thought up by someone who forgot his high school Latin. There are several others. All of these storage media work well. About the only consideration is price. Check it out on the web. The price of storage keeps dropping at a great rate.

How many pictures can you get on a flash memory card? Nowadays practically any reasonably sized card will store all the pictures you want to store. My Nikon D800 produces raw files that run between 40 and 50 megabytes. I use a 32 gigabyte card on that camera and I can store more than 400 raw files.

Image Stabilization

Most manufacturers nowadays provide image stabilization features in cameras or lenses. Both reduce camera shake enough that if you're really steady you may be able to hand-hold shots at or near 1/4 second or even slower. Cameras with the feature in the camera body stabilize things by moving the sensor slightly in response to the shakes you transmit to it. Vibration reduction lenses move one or more lens elements to kill the jitters. I have several Nikon VR lenses that I use most of the time with my D3 and D800 and I can vouch for their effectiveness. they really do let you shoot at a shutter speed three to four stops slower than you can if you're not using VR. My Olympus Pen-f has stabilization in its body, and it gives me a four stop advantage. If stabilization is in the lens you'll be able to see it take hold when you press the shutter button. Not so if stabilization is in the camera body.

There used to be a scam run by some purveyors of inexpensive cameras. Those people claimed that their cheap cameras incorporated vibration reduction, but what they really did to reduce vibration was increase the effective ISO so that the camera could use a higher shutter speed. The result in a dim light situation usually was unacceptable noise in the photograph. I haven't seen that scam for a while, but be aware and be cautious.


Digital cameras make heavy demands on batteries. You can buy a digital point-and-shoot with a built-in battery, but the problem with a built-in battery is that if you're half way through an Epcot visit and the battery gives out you're out of the picture-taking business until you can get home and plug it in again. If you travel a lot the best solution probably is a digital camera that takes plain old alkaline AA batteries. But you don't want to use plain old alkaline batteries unless you're at Epcot and your rechargeable batteries have given out. If that happens, at least you can buy some alkalines (at greatly increased prices) and keep shooting. But alkalines won't keep going for very long in a digital camera.

One good choice is Nickel-metal hydride (NiMH) batteries which are rechargeable and don't have a significant memory effect, the effect that lowers the capacity of a nickel-cadmium battery if you don't run it all the way down each time you use it. Generally, if you leave NiMH batteries lying around they'll discharge themselves quite rapidly. If a NiMH battery sits on the shelf for a month it'll be almost completely discharged. There are a few exceptions, such as Panasonic Eneloop batteries that are engineered to hold a charge on the shelf for a long time. But NiMH batteries hold a lot more juice than alkalines when they're fully charged and they handle the heavy current draw from a digital camera better than alkalines do. For NiMH the best solution is to have more than one set of batteries and a good charger. When you get ready to go to Epcot, start charging batteries the day before you leave and make sure both (or all) your battery sets are charged up before you leave.

A lot of recent consumer cameras have come out with rechargeable lithium-ion batteries similar to ones used in professional cameras. Li-Ion batteries are fairly light, carry a lot of power, and don't run down very quickly when left on the shelf. If your new camera uses Li-Ion rechargeables buy at least two to start with and then check to see how many pictures you can shoot and how long you can leave the camera turned on before your batteries run down. Based on that experience, buy enough batteries to keep you going through the day when you go to Epcot. I've found that I can go out walking every morning for an hour or so with my Nikon D3 and shoot birds in Florida or people in Colorado and not have to switch batteries for about a month. My D800 battery runs down a bit faster, but I've never needed to carry more than two batteries with that camera on a shoot.