I've Nikoscoped and am still confused. I have a D200 and 17-55mm f/2.8 DX lens. My question is:
is my D200 and 17-55mm DX combo giving me the same field of view when I look thru the viewfinder as (for the sake of argument) if I were to look through the viewfinder of a 17-55mm FX lens on an FX body?
Or when I look thru my D200 at 17mm, am I actually getting a 25.5mm field of view, from the perspective of a full-frame sensor body?
Guessing this would be really straight forward to solve if I still had my old film gear!
The focal length of the lens is unaffected by the size of the sensor. A 17mm lens is a 17mm lens is a 17mm lens regardless of whether it's a DX/FX/APS/tiny P&S/medium format sized sensor.
It's the apparent field of view that changes. The FOV of a lens will appear to be 1.5 times larger on an FX camera than on DX camera for a given focal length.
In your example, if you put a 17mm lens on a DX camera and a 25mm lens on an FX/35mm camera and placed them the same distance from the subject you should see pretty much the same image in the viewfinder and on the resulting image. If you put a 17mm on both cameras at the same distance you would see 1.5 times more image in the larger sensor vs. the smaller sensor.
In addition, due to their design and size, most DX lenses will not create an image circle large enough to cover an FX sensor. Some lenses will create an image circle large enough but only at certain focal lengths. The 18-200 won't create any image circle large enough at any focal length.
the more I think about it, why didn't Nikon mark DX lenses by reference to the "conventional" (35mm) standard;
the lens is meant for a DX camera so mark accordingly... my 17-55 should be more accurately marked 25-83mm
Since you can use non-DX lenses on a DX body, that would lead to a different, and in my opinion, worse confusion, since a DX lens and a non-DX lens with the same numerical markings would produce very different fields of view.
I find it more natural to think of the 1.5 number as a crop factor rather than a focal length multiplier.
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Focal length is a physical property that does not change because you crop part of the image circle. The problem is that 35mm photographers used to associate focal length with field of view, this is less of a problem with larger formats since they've always had to deal with it: a lens has a different field of view on 5x4" than 10x8", same (but smaller difference) with formats like 645, 6x6, 6x7 and 6x9.
If they'd been doing that since we moved from sheet film to medium format, we'd have a 60-1000mm zoom instead of an 18-200mm lens by now. Why should someone who today starts learning photography with a DX camera care about the focal length on some ancient film format that was created by cutting an even more ancient motion picture film strip in two? Wide angle is now from 8mm to 24mm, standard is about 28-35mm and telephoto starts at 50mm. Get used to it, it's not rocket science. Or pay the extra $1300 for an FX body.
Plus you'd need an LCD display on lenses with a 35mm image circle that changes when you mount it on a DX camera.
I found this old topic in my search. Time to bring it back alive as I have a question after reading the above.
When I place a 17-55mm DX lens on the FX D800 body, the D800 recognizes that it's a DX lens so it will switch itself in 'DX mode' (or however it's called). Does the field of view of the (bigger FX) viewfinder change as if the lens were mounted on a DX body?
Yes - when in DX Crop Mode, the D800 shows the reduced DX frame in the viewfinder. Note that it doesn't increase the magnification of the DX area to fill the entire viewfinder, so you see the delineated smaller DX area in the centre.
Tue 05-Feb-13 07:35 PM | edited Tue 05-Feb-13 07:38 PM by four eighty sparky
>I found this old topic in my search. Time to bring it back >alive as I have a question after reading the above. > >When I place a 17-55mm DX lens on the FX D800 body, the D800 >recognizes that it's a DX lens so it will switch itself in 'DX >mode' (or however it's called). Does the field of view of the >(bigger FX) viewfinder change as if the lens were mounted on a >DX body? > >
A 50mm FX lens on an FX body will show this in the VF: