The Nikon D80 is a popular choice in Digital SLR

SLRs, or single-lens-reflex cameras are the choice of most avid amateurs and professional photographers. The light path for both viewing and taking comes through the lens (TTL), thus there is virtually no difference between what is seen through the finder and hot the image ends up, even with close-ups. The light travels through the lens and hits a mirror inside the camera; this reflects the light upwards into a pentaprism (a mirror box) which then travels the light toward the eyepiece viewfinder. The mirrors are what give the camera the "reflex" name; "single lens" refers to the fact that one lens is used for gathering light.

The shutter is contained within the camera body and may be composed of curtains or blades. Because the shutter is composed of a leading and following set, very fast shutter speeds (up to 1/8000 second in some models) can be obtained. (In lens/shutter cameras high speeds are generally limited to 1/500 second.) Lenses are interchangeable, and cover a very wide range of focal lengths, giving access to both very wide and very long telephoto angles of view. Focusing is manual or automatic, depending upon the model and lenses used.

In each case, the focus is seen in the viewfinder; when combined with a depth of field preview feature, or when using depth of field indicators on the fixed focal length lens barrel, the photographer can judge what will be sharp and unsharp in each image. This is a key advantage over all other types of cameras.

Virtually every SLR has automatic exposure control; most also allow control over very fine nuances of exposure through overrides, compensation and other built-in features. Some exposure control systems are highly sophisticated, relying on computers to do virtual scene and lighting evaluation. Automation is now tied in with flash exposure as well, a feature that opens up many new possibilities for creative photography. Many SLRs also offer very high framing rates, with some high-end models delivering up to 8 frames per second (fps).

In short, the SLR displays the height of technology in photography today. Innards sport a host of microprocessors, micromotors, and finely-tuned sensors that literally analyze scenes and subjects, and drive all the systems that make for easy handling. While automation does cover many shooting situations, SLRs can also be customized by the photographer, a key to creative picture control. Buying an SLR means buying into a system, with all the lenses, accessories and options that open the door to virtually every type of image and subject matter. This full-system approach is what puts the SLR into a class unto itself.

The wide appeal of the SLR means that there are many models from which to choose. Options range from SLRs that are like point and shoot camera with interchangeable lenses to highly sophisticated instruments that offer superb automation coupled with the capability of photographer customization to virtually every shooting scenario. When you purchase a SLR you join a system of lenses and accessories for everything from fully automated flash photography used by professionals to special gear for close-up and special interest work.

There are a number of options to explore. In many cases your budget will help make the choice, but don't base your buying decision on price alone. If you can get all the features you want for a few extra dollars you won't regret it, as you probably will be working with the camera for a very long time. Many photographers limit their choices, only to find that they want to get a higher-featured camera later as their experience and understanding of photography expands.

Exposure Modes: An exposure mode is a way of setting up the camera's exposure system. Most every SLR today offers automatic exposure (the camera sets aperture and shutter speed for you). The most important options within auto exposure include Program (the camera makes all the exposure decisions); aperture-priority (you set the aperture and the camera selects a shutter speed); and shutter priority (you set the shutter speed and the camera sets the aperture for you). Be sure to get a camera that reads out the aperture and shutter speed values in the viewfinder. This is essential information for creative photography. Some cameras also offer Picture modes, pre-programmed solutions to exposure calculations. Portrait mode, for example, sets a wide aperture for minimum depth of field; Action mode selects the fastest possible shutter speed for freezing motion; and Landscape mode sets a narrow aperture for maximum depth of field. If you're just learning about photography these modes can help you maximize your photographs. If you know how to make settings that accomplish the same thing you don't need these modes.

Exposure Metering Patterns: Many SLRs today have very sophisticated metering systems that analyze a scene and make calculations based on algorithms that have been pre-programmed into the camera. This may be called Matrix, Evaluative or Intelligent metering, or something to that effect. Other options include center-weighted and spot metering. Those who have more experience or who want to expand their photographic knowledge should look for the full host of metering system options. If you don't want to bother with exposure calculations you won't need a spot metering option.

Manual Focus and Exposure: Some teachers feel that students should begin with a manual focus and exposure camera to learn the basics of photography. These cameras have exposure systems, but they suggest, rather than set actual exposures. The user must set them him or herself. The same goes with focus. This is one approach that is not universally accepted. If this appeals to you there are a number of excellent manual focus and exposure cameras on the market aimed at the student and those who want to learn this way. These cameras are usually less expensive and generally have less options in lenses and accessories.

Focusing: Most SLRs work with autofocusing systems. Some work with a single focus spot in the center of the viewfinder. This means that the subject focus must be set by placing the centered autofocus detector over the subject. The composition can be changed via use of an autofocus lock button that holds focus even if the subject is off center in the frame. More sophisticated SLRs have multi-autofocus detectors in the viewfinder. The system usually prioritizes the subject closest to the photographer. Some SLRs have autofocusing systems that follow moving subjects well or predict motion to help maintain focus in action sequences. Most every SLR with autofocus has both single and servo autofocus modes. Single means that the camera will not allow exposure until focus has been confirmed; servo is used with moving subjects. The former is best for portraits and still life photography while the latter is used for wildlife and sports work. The speed of autofocus is key and some high-end cameras offer autofocus tracking as fast as 6 frames per second, or faster with certain accessories and lenses.

Framing Rates: Framing rate means the number of frames-per-second the camera will fire. Framing rates range from 1 frame per second to as high as eight frames per second. If you photograph sports or wildlife on the wing the higher framing rates are preferred.

Customization: While the SLR out of the box is pretty impressive, some cameras allow you to customize the settings to your own way of working. This have on board microprocessors that can be programmed through push-button menus on the camera. Some even allow patching to a computer with even more customization options, or remote operation of the camera. This customization can be applied to the way the camera focuses, exposes and even how certain buttons and dials on the camera perform...

Ease of Downloading: The reason you use a digicam is for instant digital images without conversion from film. To work on and send or share the image you have to get it into a computer. Some digicams allow for a direct patch to the computer via parallel, serial or USB connection, or even use a SCSI adapter. Some even offer infrared download. Perhaps the easiest method is to use a memory card and use a card reader, a drive into which you put the memory card to patch directly to the computer. This eliminates the need for direct wiring between camera and computer.

User Input: Perhaps the most important aspect of SLR choice is the way the camera is designed for user input. Because an SLR is a creative, spontaneous picture taking machine, the user should be able to work nimbly with all controls. For example, many SLRs allow for exposure compensation, a way to override the camera-recommended exposure for a creative or interpretive touch. Some cameras use handy dials for this input, while others may require more extensive workarounds. This idea extends to viewfinder information. While too crowded a finder will be confusing, the photographer should have all the information required at eye level, rather than having to looking at on-camera dials or a body mounted LCD.

Full System Approach: An SLR body can be an investment. Be sure to explore the system of lenses, flash, accessories and other features that surround it. When you buy an SLR you buy into that system as well.

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