Fov

[curmudgeon_01]

Quick question -- Is the Field of View from lens designed for a crop body ,on a crop body different than a lens designed for a ff body, on a ff body? For example, a 100mm EF-S on a 7D vs a 100mm EF on a 5D.

I keep see advice similar to "since you have a crop body, you need THIS focal length" with no mention of whether or not the lens is meant for a crop body or not.

[OsmosisStudios]

FOcal length is focal length: it doesnt change. In fact, if you could place your EF-S lenses onto a full frame camera, you'd see REALLY wide, but you'd have black corners.

What changes between the two is the size of the iamge circle projected by the lens. When light enters the front, it passes through the lens and is projected out the back onto the sensor. EF lenses need to project an image the size of the full-frame sensor (and do), while the EF-S lenses are designed to project only for the smaller APS-C sensor.

If you can imagine that, you can imagine how an EF lens on a APS-C sensor camera body would leave alot of the image off the sensor (since the sensor is only seeing the centre portion). That's what leads to the x1.6 crop factor.

As you know, however, the only thing that changes with lenses is the field of view, not the other characteristics of a given focal length.

So, in short:
100mm will always be 100mm, it'll just look different depending on which body you have it on because the body will see a different field of view. This is NOT EF/EF-S dependent.