My personal reasons for doing this modifications isn’t really important. Long story short, I bought the 10-22 when I was using a Canon EOS 20D. I loved the lens, and it was my most used lens by far. Moving up to the Canon EOS 5D Mark II (a full framed camera) I knew I wouldn’t be able to use my 10-22mm EF-S mount – and it was my main concern at the time, but I hoped that my 28-70mm lens would be wide enough on a full frame… well I still missed a really wide lens, and since I don’t have an unlimited budget for photo gear… what to do.
I was under the impression that a lens made for an EF-S mount would never work on a EF mount, be cause the lens wouldn’t cover the hole sensor. However from other articles on the net I learned that this was not entirely true for the 10-22. From about 16mm the entire sensor would be covered on a full frame camera, and the back element of the lens would clear to a EF level from about 12mm.
I have been looking at the Canon 17-40mm L lens for a while, but where told by people owning both the 17-40 and the 10-22, that the 10-22 where a superior lens. I don’t like to start a debate over this statement, for me it was enough that the 10-22 where comparable to the 17-40.
So, how to you turn your prised 10-22mm EF-S lens into a great 16-22mm EF lens? Well as we will see later the result turned out to be a 13-20mm EF lens, where the 13 to 16 mm isn’t really usable, but otherwise a fantastic lens on a full framed camera.
If you’d like to try the same you can take inspiration from the steps below. And of course a disclaimer: If you decide to try this modification you do so at your own risk, I take absolutely no responsibility for the result.
1) Seen from the side it obvious how the EF-S mount protrude beyond what would be the base of the EF mount. The first exercise will therefore be to remove the EF-S mounts extra depth, since this prohibits mounting the lens on a full frame camera like the EOS 5D Mark II. The extension also protects the rear element of the lens between 10 and 13 mm, but prohibiting this extension is a problem we’ll address later.
2) First of all we need to remove the EF-S extension plate, this is done very easily: First set the lens to 22mm, this will retract the rear element as far back as it can, and will give you room to insert your finger into the hole, and hock it around the edge.
3) Pull firmly, but not virulently, up and the plate comes off very easy.
4) Having removed the back plate it is now actually possible to mount the lens on a full framed Canon body. And indeed this can be used as quick and temporary fix to mount the lens on a body like the EOS 5D Mark II. Be careful however: From 10 to about 12 mm the rear or back element of the lens protrudes so fare back, that it will hit the mirror of the camera, in best case creating an error in worst case damaging the mirror or the mirror mechanism.
5) Although we can do without the back plate all together, the best thing would be to modify it to a EF plate, since it protects the electronics in the lens and helps block out stray light that might otherwise bounce around in there. The problem however is that we cant just grind away the excess plastic, since there a grove around the inner tube. If we did remove the plastic we would be left with a detached inner tube.
6) Solution: Epoxy, you can get epoxy glue in small quantities in most countries, often in the form of two dispensing tubes. Mix a little, but enough epoxy (you don’t want to run out in the middle of pouring).
7) Before you pour epoxy into the groove, make sure it is free of dust and grease.
8) Pour just enough epoxy mix into the groove as to fill it completely, make sure you do not let it overflow, or sit too high, since this can hinder the plate in fitting over the electronics in the lens. Let the epoxy harden for 48 hours, or however long the mix you use requires to harden completely. If you are unsure, make a little test piece with some leftover epoxy, that you can test on.
9) Okay, so the epoxy has hardened. Now it is time to grind down the plastic plate, so it has the same height as an EF plate.
10) First of all remove the rubber ring, this comes off easily.
11) You are now left with the bare plastic. There are many way to remove the bulk of the plastic. I stated off with a hacksaw and switched to a knife, working my way down.
12) When you reach the stage seen here it is time to switch to fine sandpaper, to take the remaining surplus, and get a nice polished surface.
13) All done, that is to say you can stop working on the plate now and pop it back on the lens, or you can give it the finishing touch with a little mat black spray paint.
14) After painting, let it dry, completely – not sure what paint fumes can do to a lens, but why experiment?
15) Paint completely dry, pop the back cover back in place on the lens – step back and admire the result – looks like and EF mount to me.
16) Now, the problem of the back element extending beyond the back of the lens, and colliding with the mirror. The trick I used was to make a stop on the top of the lens, between the protective filter (you do have one on the lens, right?) and the front element. This element will extend furthest out at 10 and 22 mm. If you make a stop between the filter and the element 6 mm wide it will hinder the lens going further back then to 13mm, unfortunatly it also hinders the lens going beyond 20mm, effectively limiting the lens to a 13-20mm zoom. Personally I’m fine with this trade-off, since it ensures that I don’t accentually set the lens to 10mm and damage the mirror. So my solution: cut a piece of plastic ca 1mm thick and 6mm wide, and long enough to snugly reach all the way around inside the lens. The strip should be mat black to hinder reflections, so use black plastic, or paint it mat black.
17) Remove the protective filter and fit the plastic strip inside, and check that you have the correct limit – most importantly that the back element of the lens can’t extend beyond the rear of the lens.
18) Fit the filter back on. And check the limit on the lens again. Better safe then sorry.
19) That’s it, all done, you have converted the excellent Canon 10-22mm EF-S to a Canon (based) 13-20mm EF lens – and I doubt you’ll be sorry.
20) Okay a couple of test shots: this one is 13mm, you can clearly see that the image from the lens doesn’t cover the hole sensor.
21) Still 13mm.
22) But at 16-17mm it is completely covered, at 16mm you will see some strong vignetting, but at 17mm, like this image, it is a lot better – in fact I’m very happy with this result.
23) 17 mm again.