Wednesday, May 23, 2007
Do You Need A Full-Frame D-SLR?
There are significant advantages to D-SLRs that are designed around sub-full-frame image sensors. Before you decide that only full-frame will do, consider all the angles.
The term “magnification factor” was adopted to explain why a photograph taken with a 100mm lens on a film camera doesn't look the same as a photograph taken with that same lens on a camera with a sub-full-frame image sensor. Magnification factor is better than saying “35mm equivalent,” but it still isn't correct. “Crop factor” would be a more accurate way of describing what's going on as the image is being formed on the sensor.
All lenses generate an image circle of a specific size on the image plane. That image circle doesn't change no matter what kind of image sensor or film is being used. The sensor (or film, for that matter) simply determines how much of that image circle is creating a photograph. The rest of the circle becomes non-imaging light. So, essentially, the sensor or film is cropping a portion of the image circle to create the photograph.
Taking the discussion a step further, consider the various formats—35mm, 2 1⁄4 (or medium format), 4x5, 8x10, etc. If you've shot with these formats, you know that you've never contemplated magnification factors with any of them. You simply got used to the way a 300mm lens looked on a 4x5 versus a 35mm camera. On both cameras, the lens focuses at the same distance from the image plane—300mm.
The point here is that cameras with sub-full-frame image sensors tend to take a beating in professional circles because the magnification factor implies that a device is in some way inadequate. That reputation isn't deserved.
Advantages Of A Sub-Full-Frame Sensor
Cost. One of the primary benefits of sub-full-frame sensors is that the sensors themselves are relatively easy and inexpensive to produce—at least compared to the full-frame bodies. The cost savings translates into a less expensive camera. And it's not just the sensor that impacts the price. The other key internal components in the camera can be less expensive because they don't have the same loads that a full-frame sensor demands. The ability to use lower-priced components cascades throughout the camera.
Speed. A sub-full-frame sensor is generally faster than its full-frame counterpart. The sub-full-frame sensor tends to be lower resolution and generates a smaller image file. These factors combine to make the camera faster when you're shooting and faster when saving to the card. Consider the Canon EOS-1D Mark II N, a brand new camera that refines and improves upon the original EOS-1D Mark II. Canon is building this camera despite the fact that it now has two full-frame SLRs in the lineup. The camera is built for users who place a premium on speed versus resolution. You know who you are.
Workflow. Images generated by smaller image sensors generally make for a faster workflow because the image files themselves are smaller. You're not taxing your computer as much, the images open faster, they save faster, they can be batch-processed faster—all in all, efficiency is improved across your workflow.
Resolution. What's this doing under advantages? I'm glad you asked. We've already discussed how a lower-resolution image sensor can be an advantage, but what if you need higher-resolution images? The clear advantage that full-frame sensors had in this arena is eroding. The Nikon D2X was introduced this past spring with a sub-full-frame sensor that sports 12.4 megapixels. That's only about 25% fewer pixels than the current king of resolution in this class of camera, the Canon EOS 1DS Mark II (16.7 megapixels). If you need resolution, you don't necessarily have to go full-frame.
Page 2 of 3