Rigidly mounting an odd combination: T2i + 85L f/1.2

[ChadS]

@dsiegel That's a cool image. Sadly, I deal with droplets and microscopic ice crystals. Not even a snowflake amongst the bunch!

[dsiegel5151]

Ha, the only crystal I ever deal with are when my students do a poor job staining grids for TEM, and those aren't the kind of crystals you'd want to look at!

[ChadS]

Wow, lots of techy-nerd-types on this forum. Guess I'm in the right place!

[conropl]

I need to have less than 1 pixel's displacement over a series of 1000 captures or so. The trouble is the mirror slap. I know how to lock it up and then shoot a picture but I'd love to leave it up and locked out of the way. Anyways, 1 pixel of motion is about 40 micron at 3 feet away (gotta love mixed units - at a meter away) which is about 8 arcseconds of displacement.

ChadS:
With your tolerance, I do not think the play in the mount of the lens to the camera will allow that. There is a fair amount of rotaional slop in the connection to the camera body. You need to find a way to fix the lens rotaionally to the body if you want that kind of tolerance. My lenses I can feel that rotational play, and it is quite significant on some (such as my 100-400L).

As for fixing the mirror up issue - all you have to do is use live view, and then the mirror stays up.

[ChadS]

@conropl Thanks, I plan to stabilize the camera body and lens. Everything is a rigid assembly so I can smother everything with beanbags once I'm set and ready to go. Nothing like added mass to damp oscillations.

I've been playing today and have had a modicum of success so far just hacking a few things I've got on-hand (and wow the 85 has some sharp IQ even at f/1.2). I'm shooting in live view as that's the way I have to focus. However, I can clearly hear the mirror slap. I'll pull the lens and verify that the mirror is, in fact, moving up and down. Obviously the shutter must still fire but that's not a lot of vibration - though it would be a simple matter to make an external shutter. However, I don't think I can hack my T2i to still expose when the shutter is disabled and open.

[conropl]

I'm shooting in live view as that's the way I have to focus. However, I can clearly hear the mirror slap. I'll pull the lens and verify that the mirror is, in fact, moving up and down. Obviously the shutter must still fire but that's not a lot of vibration - though it would be a simple matter to make an external shutter. However, I don't think I can hack my T2i to still expose when the shutter is disabled and open.

You could not be getting a live image on your LCD if the mirror was down, the mirror would block the sensor if it was not up. You must be hearing the shutter.

[ChadS]

You could not be getting a live image on your LCD if the mirror was down, the mirror would block the sensor if it was not up. You must be hearing the shutter.

I just confirmed (by removing my lens and looking at the mirror) that the mirror returns to the lowered position after the shot is exposed briefly before returning up. Why this is, I do not know and perhaps other bodies behave differently. And it happens after the exposure so most people would not notice the mirror slap as moving the camera for the image. However, since I'm planning on shooting a thousand or more photos from one fixed position the cumulative effect of having the mirror slap the housing could add up.

Anyone really know how to drive the USB commands outside of the documented set? I'd love to park the mirror up and leave the shutter open and yet still turn the sensor on and off when I hit the trigger. I could easily add an external shutter that's far more reliable than the one in my camera. Thanks!

[Dr Croubie]

just a thought, if 85mm and f/1.2 is what you need for field/depth of view, try checking out one of these:
http://www.ebay.com.au/itm/Repro-Nik...item2c630fb122
It doesn't have a real lens mount, just a 52mm thread (so you can construct your own mount maybe including a tripod-ring) with a reversal adapter, or bellows (because it doesn't have a focussing helicoid, i hear the nikon pb4 is good, includes swing-adjustment). Not made for infinity-focussing (same as the mpe-65), and from what I hear, it's sharp as all hell straight from f/1.0. Also, for all that, surprisingly cheaper than the 85 f/1.2L...

[Dr Croubie]

ps also, with that manfrotto-mount i suggested earlier, it does have a 'minimum lens-body distance' if you didn't see that. A few seconds with a hacksaw can shorten the front-plate so that it slides further back, so that shouldn't be an issue...

[ChadS]

@DrC thanks for the heads up. I was totally unaware of that lens. See I should have asked all of you first! I've got the 85 f/1.2 on my camera now and it's performing far better than I could have ever hoped so I'm happy with things so far. However, now that i know that lens exists I will have to find a use for it...

p.s. if you only illuminate only with green light and you operate at the minimum focus distance of the 85 f/1.2 the final resolving power is not limited by the lens but by the sensor itself even wide open - at least for any current-generation EOS (the 4.3 micron pixels on my T2i are about as small as they come now). I may have to go get some crappy cell phone sensors just to find where this lens falls apart. The blue light focuses reasonably well but the red isn't close. It's at least half a pixel off! *sarcasm off*

edit: dumb question, how can a lens with a 52mm thread and an 85 mm focal length have an f/1 aperture? Ah, it can't image to infinity so it doesn't need a full 85 mm clear aperture. I'll shut up now but will leave this edit in.

edit 2: Apparently it's 0.9X to 1.1X so not a very large range. That makes the overall field of view not much more than 15mm (for my case) whereas my customer has decided 75mm is more appropriate.