Tamron 11-18mm @11mm – Nikon D700 – FX mode
I’d always wanted to do this, so I did it. :) The other day when I was at the garden, after I had finished shooting. I took my Tamron 11-18 mm lens, a DX (1.5 crop) lens and put it on my D700 and took a photo. Must to my surprise, I saw an this image, without the lines, of course. The D700 didn’t recognize that this was a DX lens and automatically switch into DX mode. A little research indicated that this switch would only happen automatically if the DX lens was a Nikon lens. 3rd party lens, not supported.
However, this was a good experiment. When I downloaded the photo into Lightroom, it was very apparent that DX lenses produce a much smaller circle that cannot cover the full sized sensor; therefore, the DX lenses, although they do cover the same viewing angle, so to speak, as a regular, FX lens, the image circle is much smaller, so only the center portion is used.

As you can see in this photo, the edges are a bit wider than the image, but are circular. This also explains, for me, the vignetting at the edges of the frame on DX lenses as the manufacturer tries to use as much of the image circle as possible.

They say a picture is worth a thousand words. This explained a lot for me. I don’t think that I’ll be trashing my DX lenses anytime soon, especially since I still have a D300, besides, they could come in handy, especially that 11 – 18mm until such time as I get a full-frame version of it, like the Tamron 14mm!

Even though you only get 1/2 of the pixels, down from 12 to 6, the image quality is still quite good. I don’t worry about that as I got great prints from my 6 MP Nikon D40 when I owned that.

The other shot is the 11-18mm lens in DX mode on the D700. The flowers were about 6 inches from the lens, the tree just about 50 meters back.

About the comfort zone?
I can see Cuba!