| Joined: | Thu Apr 12th, 2012 |
| Location: | Denham, United Kingdom |
| Posts: | 293 |
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As JK says, the focal length of all lenses is as stated on the lenses.
Nikons DX lenses have a smaller image circle, (cheaper to produce). They can be used on FX bodies but the FX body will switch it's sensor to DX area by default, if you disable that you get extreme vignetting outside the DX image area. That's it. Some DX zooms do go some way to filling the FX sensor at the wide end I believe but I have never experimented.
Soon after getting my first D3 I was in Cornwall with the D3, D2Xs Sigma 28-70 f2.8 and a Nikon 17-55 f2.8 plus a 70-200. After about one day I discovered that the Sigma was producing exposure errors on zooming. That left me little choice but to use the 17-55 on the D3. This worked well as long as I kept the focal length above about 24. For the rest of the trip I managed with 24-55.
So some DX lenses do work on FX but others, I suspect, don't.