Histogram: 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 (film or CCDs) 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. They also have less latitude than fast black and white film. 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 very 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.

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.

Storage: 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? Well, it depends on the resolution of the picture and the amount of compression you’re using. If I shoot a picture on my Nikon D2X in TIFF mode at full resolution it’ll produce a 36.5 megabyte file. That means I can’t get more than about 26 TIFF pictures on a 1 gigabyte memory card. But if I set the camera to shoot "Small" 2144 by 1424 pixels and then use a JPEG compression ratio of 1:16, I’ll end up with about a 390 kilobyte picture file and I’ll be able to get 1900 of them on the same 1 gigabyte memory card. But the quality of the photographs will be a lot lower; too low to make what I'd consider adequate prints. I shoot raw on the D3 and D2X. That gives me a full resolution file of less than 20 megabytes and a picture I can print at sizes up to 20 by 24 inches without losing quality.

Image Stabilization: During the past couple of years several manufacturers have come out with image stabilization features in cameras and 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. Cameras with the feature in the camera 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 a couple of Nikon VR lenses that I use most of the time with my D3 and D2X and I can vouch for their effectiveness. they really do let you shoot at a shutter speed three stops slower than you can if you're not using VR.

There's also a scam being run by some purveyors of inexpensive cameras. These people claim that their cheap cameras incorporate vibration reduction, but what they really do to reduce vibration is increase the effective ISO so that the camera can use a higher shutter speed. The result in a dim light situation usually is unacceptable noise in the photograph.

Power: 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.

There are at least four kinds of batteries in use in digital cameras. Some point-and-shoots come with a non-rechargeable lithium-ion battery pack that has a very long shelf life and that’ll give you many hours of shooting before it runs out. But these battery packs are very expensive, so you probably want to stow the one that came with the camera in your camera bag for an emergency. Nickel-cadmium rechargeable batteries are another possible choice but NiCad batteries have a memory effect that reduces their capacity if you don’t completely discharge and recharge them each cycle.

One good choice is Nickel-metal hydride (NiMH) batteries which are rechargeable and don’t have a really significant memory effect. But 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. 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. For a complete rundown on current NiMH batteries go to “The Great Battery Shootout” at http://www.imaging-resource.com/ACCS/BATTS/BATTS.HTM.

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. My Nikon D3 and D2X both use Li-Ion batteries and I've found that I can go out walking every morning for an hour or so and shoot birds in Florida or people in Colorado and not have to switch batteries for about a month.

<<<BACK        MORE>>>