This came up in conversation with a friend and and I want to make sure I am correct with respect to the 1.5 crop factor on standard vs. DX lenses.
If for example I am using my 80-200mm f2.8 AF-S lens on my D200 it is the equivalent of a 120-300mm lens. If however Im am using a 18-200mm DX VR lens, it is 18-200 still because of the DX lens factor, or are they both subject to the 1.5 crop? I.E. the 18-200 acts as a 36-300.
I think I ended up confusing myself on this and just want to be sure.
It is important to remember that a 50mm is a 50mm lens whether it is mounted on a view camera, medium format, 35mm, APS or DX. It is the angle of view that changes. The smaller the film/sensor, the narrower the field of view. We tend to talk in "35mm equivalents" here because we are used to the field of view that 35mm film gives us with any give focal length lens. That's why we say "a 100mm lens equals 150mm on a DX sensor." That means that when we put a 100mm lens on a DX camera, the field of view that we get is the same as what we would have with a 150mm lens on 35mm film. But again, the 100mm lens is a 100mm lens no matter what it gets mounted on.
All of this comparison to 35mm film equivalents is probably going to slowly but steadily disappear. More and more people are getting into photography never having used 35mm film at all. For them, comparing the field of view of their lenses to what it would be on a 35mm film camera will be meaningless.
It's important to realize that the crop factor is caused by the sensor, not the lens. The lens itself is still the same lens, and is not responsible for the crop factor at all. It and its focal length don't factor into the crop factor at all.
This whole thing has to do with the fact that the sensor is smaller than a frame of 35mm film is. It thus captures less of the image being projected by the lens. This lesser amount is the cropping for which the crop factor is named.
Thanks guys. That's what I had thought, but just wanted to make sure I wasn't confusing myself. I was aware that the size of the sensor dictated the amount of crop. The confusion came in with the DX designated lenses being designed to compliment the sensor sizes found in the DSLR's and thus "compensated" for the crop and listed as an equivelent.
Actually, the reason why those lenses are "DX designated" is because of the size of the image they project. Use them on a film camera and they will only cover the film partially. Since they are covering a smaller area, less glass is needed to build them. But otherwise, "a millimeter is a millimeter" You should read the Nikon document explaining their decision to remain with the DX format. You will find it here: <http://www.nikon.ca/pdf/the_dx_story.pdf>