This modification is nothing quite new… somebody hacked this quite before me, that is to remove the EF-S plastic+rubber and mount it on full frame. I decided to try it myself since I happened to have access to both (not my lens).
In practice, it is quite usable from 16mm onwards, there will be serious vignetting and risk of mirror hitting wider (as the lens element protrude out of the plane where the mount is). Technically the 16mm on full frame should have enough coverage right? So I decided to do a very quick non scientific test.
Cameras used: Canon 5D mk II and 60D.
**WARNING, shoot at 10mm at your own risk! Don’t complain if I never warn you. The 10mm full frame shot was achieved with using live-view at 22mm, then zoom to 10mm. You may risk damaging either the lens or the mirror if you didn’t do it properly.
Now you may also realised I provided few full resolution samples including focusing center and focusing corner. Supposedly full frame should have shallower depth of view so this is expected. What’s interesting is, at same focal length comparing side by side with crop sensor. Something more interesting is, the ‘optimized’ APS-C picture is significantly brighter than my old 5D mk II, either my equipment is having some problem or some unknown optic behavior. You may argue that “coz the lens is designed for crop you idiot!” Hey, even if you look at both crop and ff at 10mm:
Note the full frame shot I mistakenly taken at F3.5, yet the crop F4.0 is still brighter. Maybe my camera is getting old.
Let’s look at 100% crop (the shots by APS-C has been sized up to match with the resolution):
Note that with the APS-C, I didn’t even bother to switch focus coz the depth of field is negligible.. wait… then why do I still have shallow depth of field on full frame even at both 10mm? This is some interesting observation, I remember somebody had proven ‘any camera at equal focal length should produce the same bokeh at the same crop’. I do not know the answer, and this quick test is not purposed to investigate into that. Perhaps you can help answering it by commenting below 🙂