ZWO-EOS-T2-Ⅱ adapter for ASI533mc

Bob_Gardner

I recently purchased an ASI533mc camera and a ZWO-EOS-T2-Ⅱ adapter to connect it to my Canon EF lenses. When I use this adapter to connect the 533mc to the Canon FE mount on a Samyang 135mm f/2 lens, I am unable to get the lens to focus. The lens appears to be nowhere near focus. When the focus ring is rotated all the way to the stop at infinity, Arcturus looks as big as a baseball. When rotated the other way, Arcturus gets even larger. I am able to focus this same lens on my Canon camera, no problem. I don't see any specs for the ZWO-EOS-T2-Ⅱ adapter on your website, but have measured it to be approx 31 mm long. If I understand the specs correctly, the 533mc has a back focus of 17.5mm (with the 11mm nose piece installed). This amounts to 31 + 17.5 = 48.5mm, or 4.5mm longer than than the 44mm back focus distance required by Canon FE lenses, which I suspect is the reason I can't focus it. Respectfully request advice on how to proceed!
Sincerely,
Bob G

w7ay

Bob_Gardner This amounts to 31 + 17.5 = 48.5mm, or 4.5mm longer than than the 44mm back focus distance required by Canon FE lenses

Bob,

The ZWO adapter should come with a detachable 5mm spacer. The one that I use for my All-Sky camera (Samyang Fish-Eye) does.

Remove that spacer before you use it with cameras that have 17.5mm flange distances. Include the pre-mounted spacer only for cameras with 12.5mm flange distances.

After removing the spacer, the adapter that I have is about 26mm thick. Measure 5mm from the T2 end of your adapter, and you should notice the seam of the spacer.

You may also need different shims when you use the adapter with or without a filter. Delrin spacers come with the ZWO adapter, but you may want to get stainless steel M42 washers.

Chen

Bob_Gardner

Thank you! I wondered if that knurled piece on the end of the adapter was supposed to come off - I actually tried several times to unscrew it, but it was on so tight, and I wasn't really sure if it was detachable, so I gave up. I thought the 5mm spacer was the threaded piece that came in a separate envelope, but now I see that it has external threads on it, so its some other kind of adapter. Anyway, with your hint, I was able to remove the 5mm spacer and will test the lens again.
Thanks,
Bob

jcdavis1966

I had to do the focus mod to make it work
https://www.youtube.com/watch?v=Yk2myVjAFlU&t=50s