Understanding Mounts

[Beh162]

So I was looking at some alternate lenses and trying to see if they would fit my Camera. I have the Canon t2i

They list the corresponding mounts as:
Canon
HSM
APO
CONV
EX
DC

From what I understand I have an EF mount but I don't see that on the list. I scrolled through a few of their lenses (Sigma) and they all pretty much list those same ones.

 

[dxqcanada2]

I think Sigma's usage of the mount of "Canon" means EF.

The others are designations for lens features.
Hyper Sonic Motor
APOchromatic lens elements
etc.. http://www.sigmaphoto.com/sigma-lens-technology

 

[KmH]

Canon has 2 mounts the EF-S mount and the EF mount

Nikon uses the F-mount.

Pentax uses the K-mount.

 

[fasihjee]

For Canon there're two types of Mount 1: EFS (are of crop bodies) - EFS lens doesn't work with full frame Canon Cameras. 2: EF works with almost every body of Canon Cameras.

Rest options you mentioned are functions of different lenses (i.e: OS: Optical Stabilization, VR: Vibration Reductions, HSM: Hyper Sonic Motor, USM: Ultra Sonic Motor, VC: Vibration Control, APO: Apochormatic Lens etc.

I added few additional feature for your understanding.

 

[TCampbell]

One little technicality. Currently, Canon _really_ only has one mount... the EOS mount (we're ignoring the older FD & prior mounts). But they have two different types of lenses, EF and EF-S. The actually coupling is identical. But there is another difference that prevents you from attaching an EF-S lens to a full-frame body.

The "-S" in "EF-S" stands for "Short back-focus". The rear-most element on an EF-S lens actually protrudes back-farther than the rearmost element on an EF lens, but the lens optics are designed to handle this shorter back-focus distance.

Since a full frame camera has a physically larger sensor, it also requires a physically larger mirror. When that mirror swings up, it would hit the rear-most element on an EF-S lens... causing damage or a jam -- regardless, it wouldn't be good. So Canon has a slight difference in the design of the full frame body vs. a crop frame body. The crop-frame body has a lip which is hollowed out to accommodate the rear-most element on the EF-S lens, but the full-frame body has a taper on that same lip -- rather than hollowing it out. As a result, an EF-S lens will not "seat" onto the flange where the lens mates, even though the mount coupling is identical.

If you REALLY wanted to use an EF-S lens on a full-frame body, you could mount it to a shim -- such a short extension tube -- and you could use it anyway (you'd get really awful image quality at the edges and corners, and of course you'd mess with the whole focus distance, but if you just wanted to crop the image down and use the central area of the image, it would technically work.

The difference between the lower lips of the bodies is deliberate... that wasn't an oversight. Canon did this to make sure someone would not be able to mount a lens to the body that would result in damage -- while allowing compatibility between the two types of lenses by using the very same mount.

I grabbed my point & shoot and snapped a quick photo of a full-frame "EF" body (5D II) and crop-frame "EF & EF-S" body (60Da) so you can see the difference.

The reason I point this out, is because for *some* accessories, you'll see something that simply says it's designed to work with Canon "EOS Mount" and they won't differentiate between EF vs. EF-S. If it's a 3rd party lens claiming to work with "Canon EOS" then you have to read to note if they claim that it's for full-frame vs. crop-frame to determine if it'll work with your "full frame" body. If you have a "crop frame" body, every EOS lens will work, so it doesn't matter (unless you have an EOS 10D... but those are pretty rare anymore).

P.S. Sorry for my hasty & lousy lighting on the 60Da photo. I just wanted to throw up a couple of quick snaps.