While a digital SLR can at first seem daunting, a lot of the fundamental components are similar to those found on compact cameras.
Firstly, let's look at the main definitions and differences. SLR stands for single lens reflex. As the light enters the lens, rather than hitting the sensor directly, an SLR has a mirror that reflects the light, bouncing it up through a pentaprism to turn the image the right way around, and finally directing this light to the viewfinder.
When you release the shutter button, the mirror moves up and lets the light hit either the film or the image sensor, and the image is formed.
Let's look at the most common parts of a digital SLR.
(Credit: Canon and CBSi)
SLR cameras generally allow the user to interchange lenses depending on the shooting situation. So, unlike compact cameras where you are limited to the fixed lens, with an SLR you can swap lenses on the fly.
Digital SLRs have larger sensors than their compact counterparts. There are several sizes found in digital SLRs, but the most prevalent are Four Thirds, APS-C, APS-H and full frame (equivalent to the size of a 35mm frame of film). Here's a comparison of their sizes relative to one another (note the diagram is not to scale).
The APS-C-sized CCD sensor from the Nikon D3000.
APS-C comes in different sizes depending on the manufacturer. Currently, the Nikon DX and Sony APS-C sensor is 23.6x15.8mm, while the Canon's is 22.3x14.9mm. Other manufacturers like Pentax have slightly different measurements on the APS-C format again.
When you're first starting out with digital SLRs, it's more than likely you will be using a camera with an APS-C or Four Thirds-sized image sensor.
Full frame sensor digital SLRs are generally more expensive than SLRs with smaller sensors as they have a larger surface area. They also have better high ISO performance, which we'll explain in the next section as we talk about exposure.
Say for example you want to take the same photo with a full frame sensor dSLR and an APS-C sensor dSLR. The APS-C camera will see less of the scene than the full frame, even when using the same focal length lens, because its sensor is smaller. This is called crop factor.
The image outlined in green is an example of cropping on a smaller-sensor digital SLR compared to a full frame digital SLR. (Credit: CBSi)
Typically, consumer Canon dSLRs have a crop factor of 1.6x and Nikon dSLRs have a crop factor of 1.5x. To calculate the equivalent (effective) focal length of a full frame lens on a smaller sensor body, multiply the focal length by the crop factor.
Another thing to take into consideration is that some manufacturers have different series of lenses depending on the camera's sensor size. Canon EF-S lenses, designed for APS-C sensors, will not fit onto a full-frame Canon body. Nikon's F-mount system is consistent between all their SLR range, meaning you can use any lens designed for a film or digital SLR on your camera but you will encounter a crop factor when using an FX (full frame) lens on a DX body, and possible vignetting when using a DX lens on an FX body.
Even though the lens mount looks very similar, the Canon EOS 5D Mark II (left) can only accept EF lenses. The camera on the right, a Canon 40D or 50D, can accept EF-S and EF lenses. Look at the white mount alignment that gives the game away. (Credit: Canon and CBSi)
Micro Four Thirds
The new frontier in digital photography over the past year and a half has been the Micro Four Thirds format which has reignited the flame in many a photographer's heart. The system was jointly designed by Panasonic and Olympus to allow for maximum flexibility for photographers who still wanted the convenience of interchangeable lenses without the bulk of a traditional SLR. In essence, Micro Four Thirds cameras are still interchangeable lens cameras but they don't have the mirror or pentaprism arrangement that characterises SLRs. Watch the video below for a full explanation of the format.
Some examples of Micro Four Thirds cameras include Panasonic's G-series of cameras (G1, GH1 and GF1) and the Olympus Pen E-P1. Essentially, the features of Micro Four Thirds cameras are relatively similar to SLRs, including manual controls, just in a smaller and more portable form factor.