can you manually focus an 85LII off-camera?

I have an 85LII and wanted to try it with my astrophotography camera, a QSI583ws. I'm wondering if focus is going to be possible, though. There won't be any electronics talking to the lens, just a dumb EOS mount. I know my 35L and 135L have full time manual focus, so they're fine. But turning the focus ring on the 85LII, even when switched over to MF, does nothing unless you've half-pressed the shutter on the camera body.

Ideas?

MF ring on the 85L is focus by wire. It only works when the (Canon) cam is turned on.

yep - only works on camera w/ camera on and for a few seconds after you turn camera off

Thanks guys. Bugger.

troypiggo wrote in post #13399263
Ideas?

You could mount the lens on a Canon EOS body, prefocus, then remove the lens and put it on your astro camera. If your astro camera has a very precise register distance, then it should work fine if not, then the focus distance will shift when mounted.

You might be able to use a helical focuser to correct for a slight variation in the register of your astro cam. That said, field flatness and image sharpness when it's wide open would be other things to consider.

It just struck me... maybe you could power the lens seperately?

The knowledge base here is just so amazing

noisejammer wrote in post #13423297
It just struck me... maybe you could power the lens seperately?

Would probably be a far bigger pain than it's worth...

Thanks guys, but I'm going to use the 35L and 135L instead. For the amount of times I'm going to do this with lenses, not worth the hassle of mucking around with the 85L focus.

Aren't the 135 and 85 a bit long for astrophotography?

Depends. What are you shooting? I have 4 telescopes at 400mm, 600mm, 1200mm and 2350mm focal lengths as well.