ef-s on ef mount?

If all that is really different is that the back sticks out a bit more, would you be able to use say kenko extention tubes an have a 17-55 work on a 5d2?

if you are able to do this, would you lose a stop?

You would loose some light depending on the tube used. You would also loos the ability to focus at distance again depending on the tube used. Why do you want to do this?

oh i dont want to do this, my mind is usually 8 places at once, so it was just a random thought, if i were to think about doing this i would prolly sell a 17-55 and pick up a 24-70.

footballdude2k3 wrote in post #8968034
oh i dont want to do this, my mind is usually 8 places at once, so it was just a random thought, if i were to think about doing this i would prolly sell a 17-55 and pick up a 24-70.

That would be best. The 24-70 on a full frame is about as perfect as the 17-55 on a crop.

It would probably work for macro shots but you lose the ability to focus to infinity so the lens won't really "work".

I tried this when I first got my Kenko Tubes (for fun) and while it works with a 12mm tube >~35mm, the shorter focal lengths can only focus inside the lens (Negative working distance). At 55mm the infinity focus is around 6-8" and if I recall correctly the corners were very much black. There is little real use for this setup beyond curiosity.

XsiBrian wrote in post #8968380
I tried this when I first got my Kenko Tubes (for fun) and while it works with a 12mm tube >~35mm, the shorter focal lengths can only focus inside the lens (Negative working distance). At 55mm the infinity focus is around 6-8" and if I recall correctly the corners were very much black. There is little real use for this setup beyond curiosity.

sounds good, thank you sir.

I've played with 60efs on a tube mounted on a 1DMKIII and works well as a macro lens with focus range from about 3" in front of the lens at 1:1 to 13" at 00. With the Canon 12 tube you keep AF.

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footballdude2k3 wrote in post #8967999
If all that is really different is that the back sticks out a bit more, would you be able to use say kenko extention tubes an have a 17-55 work on a 5d2?

the difference isn't just the mount...there's also the smaller image circle...so there will be a lot of vignetting...

DreDaze wrote in post #8969524
the difference isn't just the mount...there's also the smaller image circle...so there will be a lot of vignetting...

Not forgetting that as the lens is moved away from the sensor (by the tube) then the image circle will become larger....exactly why extension tubes result in greater magnification.

Bob