Electronic compatibility of EF-S lens on EF body?

[NancyP]

What happens when you put an EF-S lens, via electronically communicating extension tubes, on an EF body? Is there any risk of screwing up the EF body's or the EF-S lens's electronics?

I haven't tried the experiment of putting any EF-S lens on a FF body before now, mostly because without extension tubes, there can be a risk of mirror damage should the EF-S lens have a back element extension, and because one already knows that the image circle without extension will be insufficient.

I was wondering if the EF-S 24mm pancake would have a usable image circle at 1:1 on a FF body.

 

[msowsun]

There is no danger of messing anything up electronically using EF-S lenses on Full Frame cameras. With more advanced cameras like the 5D Mk III, the AF does not work using the viewfinder, but it works fine using Liveview. More basic cameras like the 6D or 5D Mk II will AF in viewfinder and Liveview.

The EF-S 24mm 2.8 will vignette badly and the mirror will hit at infinity focus.

More info here:

EF-S 24mm on FF http://photography-on-the.net/forum/showthread.php?p=17314567

EF-S 10-18mm on FF http://photography-on-the.net/forum/showthread.php?p=17046356

 

[NancyP]

Thanks for the information. That's also very interesting about the modded 10-18 STM used at 14 to 18mm on a FF.

I daresay nothing much will happen to the 6D mirror when the EF-S 24mm is sitting in front of the mirrorbox on the end of an extension tube. The view will be dim. Looking at your images on the link, I think that the image circle will cover FF at 1:1 and maybe less than 1:1. I would focus manually of course. Bleh, focusing the 40mm STM manually is a PITA - that disembodied feeling given with "focus-by-wire".

My calculations indicate that the 12mm extension tube will yield a maximum magnification of 0.77x with a working distance of 2.8 cm. A 20mm extension tube would yield a max. mag. of 1.1x with a working distance of .... 0.9 cm. I didn't bother to calculate the 36mm extension tube, working distance is likely behind the lens.

I wish Canon had a shorter extension tube, something in the 8 to 9mm range. It is a bit of a kooky idea anyway. I started playing with the few film-era wide angles I have on hand, and none had any working distance on extension tubes. The only modern fullframe option with a little working distance is the Voigtlander 20mm f/3.5 pancake lens , which is a little expensive for an experiment. I can't think of a film era lens with a similar pancake design.

I actually have a use for the unmodded EF-S 24mm on my 60D as a just in case landscape lens when I go out birding with the EF 400 f/5.6L.

 

[Deleted member 91053]

I have only tried the EFS 60mm Macro on a 1D4 with a 13mm extension tube - results were excellent!