Digital only lenses?

It seems obvious, but I gotta know for sure. Do the digital only lenses take into account the crop factor. Is the Nikon 17-55 AFS DX a true 17-55? I currently have a Tokina 12-24 f4 and I'm saving for a lens for shooting landscapes that will fill the spot now taken by my 18-55 kit lens. I think the 17-55 might be a good fit. But then I read about the Nikon 24-70 AFS FX and thought it might be the one. But being a lens for full frame cameras will I be missing some range between the Tokina 12-24 and the Nikon 24-70?

The focal length of a lens is the focal length, a physical characteristic of the lens. The "crop factor" is not taken into account. The camera's sensor dictates the "crop factor".

As Alan said. There's no gap between the 24 of the Tokina and the 24 of the Nikon (except for rounding errors, of course - so you might have a gap from 23.6 to 24.2... ).

It depends on the body. The sensor on Nikon's non-FX bodies is a little smaller, so it "sees" less area. On a full frame lens, whether newer FX or older pre-DX, it's not seeing the whole area available and "crops" out of a smaller area within the available frame. Conversely, put a DX lens on an FX body or a film body for that matter, and the sensor (or film) reaches beyond the coverage of the DX lens. You could certainly shoot the 17-55 on the FX or film body, and you'd have a lot of vignetting.

I don't know why I haven't tried it before, but I just took an 18-200mm VR DX lens off my D2X and put it on an old F90 I had handy, and it vignettes badly throughout the zoom range. Good enough answer for me.

Short answer: It depends on whether your current body is DX. If you buy the DX lens and later upgrade to an FX body or try to use a film body, tough luck. If you're already using an FX body, don't waste your money on a DX lens.

Note that Hank is talking about the size of the image circle, not the focal length. 200mm on his 18-200 is the same as 200mm on, say, an FX 70-200.

Like they said, focal length is a characteristic of the lens, not the body. 17mm is the same on any format. The difference is the film/sensor size, and what the body sees through that lens. Some see more, some less.

Ok, so on my DX body (1.5 CF) the 17-55 is approx 25-82 full frame. So, I would be getting more range on the long end than the 24-70. Sounds like the 17-55 makes more sense given that they both have excellent reviews and I have no plans of going to a FX system. However, I'm still open to other alternatives. Thanks guys.

Bruce, the crop factor of your DX body also applies to the 24 to 70 lens so it would perform like a 36 to 105 on the DX body. The crop factor is determined by the sensor not the lens so it applies to DX or FX lenses the same way. So for your comparison the 17 to 55 would act like a 25 to 82 and the 24 to 70 would act like a 36 to 105. You would gain on the wide end with the 17 to 55 but lose on the long end.

Okay thanks Bill. I don't know why I had trouble getting my head around this, it's not that complicated.