Originally posted by stewart_photo It's the same principle behind why a lens only throws at certain image area onto the image sensor, Peter. However, in this case, the image sensor is your viewfinder display, the lens is the glass prism, and the distance from the back of the lens to the image sensor is the distance from the mirror to the glass prism. To increase the image area on the viewfinder display without introducing distortions, they would have to increase the distance through the prism or the distance from the mirror to the prism. Either of those would increase the physical size of the camera. This is one reason why the K10D is smaller than those few mammoth Nikon and Canon cameras which display 100% of the image in the viewfinder.
Umm, no. Not true at all.
First of all, we are dealing with the focusing screen and not the image sensor or the film when discussing the viewfinder. The focusing screen must show 100% of the image on the sensor plane, and the view system (prism + optical lenses) must show 100% of the focusing screen.
Second, there is no issue with size or distortion with a 100% viewfinder. My Pentax LX has a 100% viewfinder and it is quite a small compact camera. [
Edit: Actually, the specs show 98% vertical and 95% horizontal.] The Nikon D300 has a 100% finder and it is no bigger than the D200 with 95% coverage. There is no engineering reason at all to not show 100% of the image. No distortion problem at all. The reason is economic (the cost of more precise engineering and manufacturing to get 100% coverage) and historical. In the past, consumers who shot reversal film and had prints made would get prints that cropped off the edges of the negative. And slide mounts may crop the image slightly. Camera makers routinely reduced the image size on consumer grade cameras to reflect what most consumers would get on their prints. However, professional grade cameras (like the Nikon F series) would have 100% finders for more control for professionals working with unmounted positive film or making custom prints from negatives.
Third, the finder in modern DSLRS is crowded with all sorts of extra info (camera settings, exposure info, flash status, etc.) In order to squeeze all that stuff in, it is tempting to cut a few percent off the image size. Most people won't notice the difference.
Fourth, the other issue with the viewfinder is magnification. With the smaller focusing screen in cameras with an 18x24mm sensor, the apparent image will be smaller in the viewfinder. You can modify the optical system to increase magnification, but you may also affect the eyepoint of the finder (the eye relief necessary to see the entire finder image). If you have any experience with telescopes, you know that a higher magnification eyepiece has less eye relief, and a better quality eyepiece with better eye relief is much more expensive. A viewing system with higher magnification and good eye relief will be more expensive, but it will be more comfortable to use, especially for eyeglass wearers. Again, a smaller image that is few percent off 100% will same some money and most people won't notice.
Last edited by GaryML; 11-30-2007 at 09:40 AM.
Reason: Corrected error on Pentax LX viewfinder