DIGITAL CORNER
By Bob Dean
Digital Sensors and Lens Performance
Digital SLRs come in two flavors of sensors, APS and full frame. The full frame behaves just like the 35mm film cameras. In other words the image from a normal lens is projected onto the film so that what the lens “sees is what is on the sensor. The APS size sensors have a crop factor and thus show a magnification ranging from 1.3x to nearly 1.7x. We discussed this is a previous digital corner so if you what a refresher, wander over to our website and review “Sensor Size and Magnification”
This is a real advantage for wildlife in that we get the extra focal length without losing the light like you would with a teleconverter. We pay the penalty with wide angle however.
There is another, more subtle advantage to this smaller size. The lens still projects the image on the sensor as if it was a 35mm film plane. That means that those parts of the image which would normally be around the edge of the 24mm by 36mm rectangle are not recorded by the sensor pixels. That, in turn, means that those problems we used to see with lenses (especially inexpensive lenses) are gone. The soft focus, distortion and vignetting are off of the recording surface.
Practically, this means that you can open up your lens to a larger aperture without seeing the edge problems that full frame or film would see. Your lens’ “sweet spot” just got better in that what you used shoot at say f/8 to reduce distortion, you may now be able to go down to f/5.6 or even f/4.
Check out your camera system and see how much improvement you can get!