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

Folks,

I've got a project where I need to rigidly mount my camera (a T2i) and an 85L f/1.2 prime to an optical table. The lens will be set to its minimum focus and the the target will be put in-focus by moving a micrometer stage until it's centered and sharp in live view X10 viewed on an HDTV. My hope is that someone in the group has a suggestion on how to mount the lens (more so than the camera) rigidly. Obviously I can mount the camera with the 1/4-20 hole on the bottom. I could mount a quick-release plate, etc. However, I'd prefer to find a mount that holds the lens first. Then I can support the body using adjustable hardware I already have around my lab.

Does anyone have a suggestion of a tripod ring or some other mount that can hold this lens without translating or spinning?

Thanks!

Interesting problem...

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Originally Posted by ChadS

Folks,

I've got a project where I need to rigidly mount my camera (a T2i) and an 85L f/1.2 prime to an optical table. The lens will be set to its minimum focus and the the target will be put in-focus by moving a micrometer stage until it's centered and sharp in live view X10 viewed on an HDTV. My hope is that someone in the group has a suggestion on how to mount the lens (more so than the camera) rigidly. Obviously I can mount the camera with the 1/4-20 hole on the bottom. I could mount a quick-release plate, etc. However, I'd prefer to find a mount that holds the lens first. Then I can support the body using adjustable hardware I already have around my lab.

Does anyone have a suggestion of a tripod ring or some other mount that can hold this lens without translating or spinning?

Thanks!

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Chad, Will you be mounting the camera to shoot straight down on the table or will you mount it horizontaly to shoot across the table?

@Bob I'll be shooting horizontally.

I forgot to ask, How far off of the table does the camera and lens need to be and will this be hardmounted or something temporary?

@Bob at the moment I've got the centerline of the camera about 6 inches off the table. However, it could be more than that. This will be something semi-permanent for the next several months but I'd rather not damage or mar the lens if I can avoid it. Something that I could take in- and out easily would be great so long as it will return to the exact spot. I'm thinking about machining something to mate to the filter threads if no other idea presents itself (with cushioning supports for the rest of the lens and body).

This might be what your looking for.

http://reallyrightstuff.com/ProductD...-Quick-Release

I think this could be adjusted to fit your needs

This is a lab setting? Walking through the chemistry labs in my building, there are large clamps to hold reaction vessels (glass or stainless steel), of sufficient diameter to hold the 85L at the wide part of the barrel (where the distance window is located). The clamps can be mounted to a ring stand (in the labs, there are mounting lattices across the back of the fume hoods). They rigidly support vessels up to several liters.

If that sounds like something that might work, I can find vendor/model information.

--John

@Bob, that looks like a nice steady rest but doesn't appear to rigidly grab the lens. @John, I know exactly the type of hardware you're discussing. However, most of the clamps I can think of have rubber-coated arms that are likely to over-constrain the lens so that depending on how I bump it, etc. it'll move and stay put.

I think I'm going to build my own steady-rest similar to what Bob linked but with some sort of mechanical fixture above. This might be a spring-loaded arm or even a Velcro strap.

I've run into this problem on many occasions but rarely get to use off-the-shelf hardware. I was hopeful this lens might have a tripod mount that's perfect for it. It's really hard to constrain something that's not designed to be rigidly mounted! If you touch something in more than 4 spots and don't allow the proper DoFs (like the wheels in the mount Bob linked) things will NOT stay put!

Similar to Bob's suggestion, I was thinking along the lines of:
http://www.manfrotto.com/telephoto-lens-support
You can then bolt the camera-lens combo straight through the table, in two or more spots.

Or how about a home-made version, look at your local hardware shop for something like this: http://www.slateandcopper.com/Portal...ut_bracket.jpg or http://www.drainageonline.co.uk/imag...pe_Bracket.jpg
you can get them with thin-rubber-lining so you don't damage the lens, and it'll hold it very steady.

Or I don't see why not just bolt the camera to the table, the 85/1.2 doesn't stick out below the bottom of the camera does it? if you bolt and/or superglue or otherwise fix an A-S clamp (like a kirk or wimberly 3-4inch eg http://www.bhphotovideo.com/c/produc...ase_Clamp.html) to the table, and put a plate/L-bracket on the camera body, you can get it back to within <0.5mm if you take it out and put it back in (once it's in position the first time, grab a sharp knife and carve some lines on the plate and clamp that line up, so you know where it goes back in place). Or is that too much tolerance too?

@DrC thanks for the suggestions. Believe it or not the 85 does stick out below the bottom of a T2i! However, for my purposes the T2i's frame is nowhere near rigid enough even if I could bolt it down sufficiently. 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. The Manfrotto support you listed is for-sale on Amazon for ~$70 and is similar enough to what I'd have built that I'll save myself the time. Tha

@ChadS my thought is, do you really have to use the 85mm F/1.2 when there are other primes that already have the tripod foot mounted.

My second thought is, 1 pixel displacement over 1000 captures, no way any of the methods you mentioned will be that rigid. You will need a system that you can recalibrate your alignment occasionally, if not very frequently. That is provided the mechanical parts inside of the lens and camera can be held to that tight of a tolerance, which I have my doubts they can.

One problem I see is that the 85mm is not made to mount a clamp in the manner you are talking about. A mount this stable would be similar to a mount on a rifle scope, a rifle scope is made to take a clamp that puts out an extreme amount of pressure. The barrel of the 85mm may or may not be made to take this pressure. You very well may damage your lens. If a clamp is the way you go, you should be looking for something that will fit around the barrel fully, otherwise you risk egging the barrel of the lens. Just the temperature difference of the non similar metals and components will make it very difficult to keep it consistent.


Good Luck with your Experiment.

@HD welcome to my world! The 85 was chosen according to a long list of criteria. I wanted to use the macro 180 but it isn't as fast at the working distances we're starting at (though we may return to 1:1 within the next few months). We considered 25 lenses from Zeiss, Canon, and Tamron and ended up with the 85 as the best choice. The 200 was close but the field of view was simply not close enough to the final project to buy and the f/# is nowhere near as fast (shallow DoF is critical to the project).

A rifle scope is designed to hard-mount to a barrel and not translate during a high-g acceleration (the bullet shot). I don't have to be so aggressive. I can let the lens breathe and flex so long as it returns on-target after the motion. I've had success in the past making my own mounts for "things" that are as repeatable as I've mentioned but I've never used commercial lens systems before (usually things like long-distance microscopes or bare lenses) so this will be a learning experience for me.

ChadS, if shallow DOF is a key point wouldn't the 180mm L give you a smaller depth of field at its minimum focus distance of 1' 6" @F3.5 than the 85mm gives you at its minimum focus distance of 3.2' at F1.2. Or how about either the 100mm macro or 100mm macro L which gives you 1' distance. Perhaps they are not giving you the framing you want, and then you could go with a FF camera which actually would even give you a tight DOF. Any of those lenses would have tripod feet available.

Of course I do not know what you are trying to do, I am just throwing out things that you may have already considered (or not)

@HD You're exactly correct. DoF goes as the 1 / magnification squared (basically). so at macro distances the DoF would be insanely thin - and we will repeat this entire project with just such a lens once we've got everything else working. However, for now the customer wants a substantially larger interrogation region than could be imaged at 1:1. Instead, the 0.1x mag of the 85mm lens works out almost perfectly. Were I to use the 180 at the same framing the DoF would be substantially thicker.

DoF is not my only issue. If I just needed thin DoF I'd use a 1000x microscope objective. And while cool, those beasties don't allow for much field of view. Thanks for the help though, fresh eyes are always appreciated.

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Originally Posted by ChadS

If I just needed thin DoF I'd use a 1000x microscope objective.

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Wow - where'd you get one of those? My highest power objectives for routine use are 100x NA=1.4 and require oil immersion, although I do have a 150x NA=1.35 glycerol immersion lens, and a 150x NA=0.95 dry lens for materials work.

@John with what occular? Magnify the magnified image man! Okay so I did say objective and not system mag. Seriously though I was just exaggerating my point. Leave it to the bio guy to catch me. :P

edit: sorry if I got you all excited for a moment... I don't do micro work. All my stuff is macro (a few microns on a side at least).

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Originally Posted by neuroanatomist

Wow - where'd you get one of those? My highest power objectives for routine use are 100x NA=1.4 and require oil immersion, although I do have a 150x NA=1.35 glycerol immersion lens, and a 150x NA=0.95 dry lens for materials work.

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Where can I get these and...do they have an adapter so I can hook it up to my 5D II :confused:

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Originally Posted by HDNitehawk

Where can I get these and...do they have an adapter so I can hook it up to my 5D II :confused:

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http://www.edmundoptics.com/products...categoryid=172
Edmund is sort of like the Walmart or Target of optical supplies. They have everything but not necessarily the high-end stuff. There are 100x objectives for Mitutoyo infinity-corrected objectives and several in the finites.

As to mounting your 5dII? Most microscopes these days have some sort of camera port that you can use instead of an eyepiece. Think your current lenses are expensive? Check out the prices of the good objectives - $21k for an 80X UV objective and that's for something that weighs about a pound.

This company sells pretty cheap adaptors for an EF mount camera to a microscope:

http://www.martinmicroscope.com/

Really nice guys too. I mostly keep my T3i on my microscope, but I also have taken nice images with my 5D and 20D. In terms of price for good objectives, ChadS is right. They are not cheap. My Olympus phase contrast objectives were roughly $5000 a piece. Thus, I paid around $20,000 (well, the university paid) for 4x, 10x, 20x, and and 40x phase contrast objectives

Male Red-spotted Newt cloaca at 40x total magnification. Canon T3i, Olympus BX40 microscope.
http://farm7.staticflickr.com/6171/6...d12aa2e7_z.jpg

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

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!

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

Quote:

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Originally Posted by ChadS

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.

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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.

@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.

Quote:

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Originally Posted by ChadS

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.

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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.

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Originally Posted by conropl

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.

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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!

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...

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...

@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.

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![/QUOTE]


Have applied to get the SDK to allow creating a custom sample imaging device, with MPE-65, with a unique interface for a grad students research project. Microscopes available use too small a sensor and the results of shifting and stitching images change the grayscale values too much for the bitmap conversion and subsequent image analysis.
The purpose of the SDK Canon provides is to allow programmers to create custom software to use in tethered operations. Might be something you want to look into. Language of source code is MS C++ 6.0

JRW

I have a copy of the SDK. The documented commands are ... limited. However, I know some of the telescope community especially has reversed engineered the software bundled with the camera and have discovered other capabilities. Unfortunately I don't know of anyone that has figured out how to pin the shutter open.

I think I'm having a good amount of luck on mounting my rig. Based on the links provided earlier I've created a steady-rest with two rollers under the lens, a spring loaded clamp to go over and a variable riser under the back of the lens (that also supports the camera). On top of this I've added about 12 lbs. of beanbags. I can go several hundred shots and not drift a full pixel (~40 micron object distance) but I'll need to wait until I get a finer positioning stage to see how well I'm splitting the pixel distance.