Tokina 10 -17 lens on Full Frame?

The 10 -17 is made for a crop frame camera , so works fine on my 7D, But can anyone explain via a technical explanation why it also works on my FF camera (5D Mark 2) at the outer zoom of 17mm??

thanks

Drew

The 10 -17 is made for a crop frame camera , so works fine on my 7D, But can anyone explain via a technical explanation why it also works on my FF camera (5D Mark 2) at the outer zoom of 17mm??

The image circle of a zoom lens varies according to the focal length setting. On Tokina 10-17 lens the image circle is always larger than the 27,3 mm diagonal of an APC-S size sensor (22.7 x 15.1mm), but unfortunately on the wider end setting the image circle is smaller than the 43.5 mm diameter, which is required to cover a full-frame sensor (24 x36mm).

This lens is designed to be a "full-frame fisheye" vs. a "circular fisheye" on APC-C size sensor. With a full-frame sensor the lens becomes more like a "circular fisheye".

The newest Canon 8-15mm fisheye can be zoomed between circular and full-frame depending on sensor used.

For a brief explanation about the meaning of the image circle, see:

http://www.bobatkins.com/photography/techn...ld_of_view.html

from where I quote:

"Note that you can't just take any lens and use a very large frame to get a wide field of view. Lenses have an image circle which is the diameter of the largest image that the lens can form. Outside that diameter the lens vignettes, cutting off the image due to the limited size of the optical elements or other characteristics of the design.. Lenses designed for use on full frame 35mm cameras must be designed to have an image circle of at least 43.5 mm, since the diagonal dimension of the 35mm frame is 43.25mm. It's very difficult to make short focal length lenses with large image circles."

Some interesting stuff about wide angle and fisheye lenses:

http://en.wikipedia.org/wiki/Fisheye_lens

http://www.bobatkins.com/photography/revie...gle-lenses.html

http://www.bobatkins.com/photography/revie...e-lenses-2.html

http://www.rugift.com/fisheye-lenses/fisheye-lenses.htm

http://panopticus.altervista.org/fishlist/fishlist.htm

thanks for the explaination, exactly what I was looking for

Drew