Case study: "Portable" stacking set-up.

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Charles Krebs
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Case study: "Portable" stacking set-up.

Post by Charles Krebs »

This is such a great forum for getting ideas since people are so willing to share their set-ups and experiences. I’ve been really impressed with some of the solutions people have come up with. Recently I had a challenge that might be of interest to some here. I thought a post like this might add to this “tradition”.

I had to take a flight cross-country with a set-up that would allow me to photograph a wide variety of subjects (stacks) up to about 20X. It had to be carried aboard the plane (to guard against delayed or misplaced luggage) and it needed to be “set up” and “taken down” quickly. Fortunately the client said they had plenty of continuous lighting (halogen and LED) I could use on site, so I didn't need to pack lighting.

At my home “studio”, cast iron and weight have been desirable, and my friends! :wink: . Suddenly I needed to re-think a few things.

So this was my traveling set-up. I took the focus post from a stereo microscope stand and made a base of maple. (I had two bases I could have used but one was too short, and the other, cast iron, was far too heavy). Three 5mm machine screws attached it to the wooden base. To the vertical post I attached an Arca-Swiss clamp. To this I attached the Velmex slide discussed here. Then, an older Pentax bellows (Thanks Betty!) was attached to the Velmex slide… again via an AS clamp. This bellows is very lightweight and locks down very tight. It also has a rotating back and enough clearance to rotate the camera to different orientations… something I find essential. It is crude in its adjustments, but that was not an issue here, as all fine adjustments were made using either the microscope stand post or the Velmex slide. The only real “assembly/dis-assembly"” were the three machine screws to attach the post to the base. Attaching the components via the AS clamps takes just a few seconds.

Five lenses were packed… 63/2.8 El Nikkor, 40/2.8 Schneider Apo Componon HM, 28/4 Schneider Componon, Nikon 10/0.21 SLWD objective, and the Nikon 20/0.40 ELWD objective.

One other piece that was very helpful and saved a great deal of time is the tilting ball & socket stage. It can be seen in detail here: http://www.snrmachine.com/st1us.htm
(I picked this up a long time ago on eBay for a fraction of the cost listed).

Everything fit easily in a relatively small, well-used Tamrac backpack bag I’ve used for years for all sorts of gear. (I won't bother to describe the expression on the face on the TSA agent when the bag went through the x-ray machine... several times :shock: )

I realized that this was too cantilevered for my taste. I would have preferred to leave out the Velmex slide and use one of my microscope focus racks as part of the base, but the only one I had set up for vertical use was semi-permanently attached to 10 lbs of cast iron, and lack of time meant I needed to “grab” as many things that were ready to go as possible. But a few tests showed that, at home, things worked great... thanks in no small part to the extremely low vibration of the Canon live-view and it’s electronic first shutter curtain. (I was actually a bit surprised at how solid it was). But one advantage to the Velmex slide was that it could be very quickly released from the vertical stand and clamped on a tripod head for "stepping" an "open" horizontal arrangement.

Image

Once set-up on site, there were a few unexpected wrinkles. One was working at 20X. The location was “big city”, on the 24th floor of a 58 story building. Also, apparently my concept of a massive, stable table was different from the clients. Even though I arrived very early one morning in order to avoid “foot traffic” in the studio, I could not work at 20X. I don’t know exactly what the problem was, but I suspect vibration from the buildings ventilation system, with possible contributions from the nearby elevators. My “cantilevered” design didn’t help things, but I don’t think that was actually the determining factor. Big buildings in big cities with lots of things going on are likely not the best places for this type of work. (Now I know why Newport gets many thousands of dollars for their damping “optical tables”). 10X shots were possible with care.

One thing that really helped was the “cheat sheet” I printed up and brought with me. I knew that we would be doing many subjects in fairly quick succession, at a wide range of magnifications. There would be a lot of discussion and many distractions, so I could not work at my usual isolated and leisurely (slow! :wink:) pace. And for these stacks it would be good to stop down as much as possible to keep the number of shots in a stack to a minimum. (Very good, rather than “ultimate” resolution was needed). The sheets I made up and used were as follows…

First was a chart that I could refer to that read out the magnification based on the lens used and the bellows extension (which was read off of a scale that was affixed to the top of the bellows rail). Then, using that magnification, I referred to a chart that color coded my possible aperture selections based on diffraction resolution loss. Green was good, yellow meant “caution”, and red indicated apertures where I knew I would not like the results. This chart also provided the number of microns I needed to “step” for each consecutive shot in a stack (70% of the total DOF). Knowing the "marked" f-stop to be used and the needed step distance, I consulted the last chart which indicated the distance moved with each “tick” mark on the Velmex rail scale. It worked out great, and it was possible to set up and shoot a stack with a good aperture and focus step with a minimal amount of “thinking”. (If you're curious the spreadsheet that I used for the charts is here: www.krebsmicro.com/DOF4.xls )

rjlittlefield
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Post by rjlittlefield »

Lovely -- many many thanks for the posting!

--Rik

DQE
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Post by DQE »

Just to confirm you suspicions about working with microscopy-related instrumentation in office buildings - at my workplace, my lab was in the basement where I had rock-steady freedom from vibration and similar things. My colleagues in other buildings who were in higher floors (even 5th floor) had essentially identical equipment but experienced much more vibration problems. This was particularly evident at higher magnifications.

Thanks for the spreadsheet!
-Phil

"Diffraction never sleeps"

Will Milne
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Post by Will Milne »

Hi

Thanks for sharing this Charles- relative portability seems to present some unique problems . I realize this kind of work is probably best or optimally pursued in very controlled situations. Great to see a workable setup that worked in less than optimal conditions. I often spend weeks in the bush - so having a rig that can come along for the ride and work is an interesting proposition.

Will

pierre
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Post by pierre »

Very nice setup Charles :shock:
Regards

Pierre

AndrewC
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Post by AndrewC »

Have you thought of moving away from a bellows and using a helicoid or fixed extension tube ? Makes it much more portable, more rugged and less "cantilevered" ? Sure you might lose some of the full framing capabilities (with the fixed tubes). You also lose the ability to rotate the body but with that nice ball mount you can just rotate the subject. Like everything there are pro's and con's.


I'm working along a few routes right now:

1) Use fixed T-mount extensions plus a Beljian for objectives
2) I've got an Olympus 65-116mm auto tube to which I've added a Nikon F bayonet on the male end - just need an Olympus to T-mount female on the other
3) I've got a couple of helicoid tubes with M42 at each end.

4) Subject stage - I'll post a picture when I'm next home but here's a verbal description of my latest stage:

- screw a steel plate to your base (unless it is already magnetic)
- grab a single piece of 3/4" loc-line tube or similar
- on the large end epoxy in a disk magnet, this will hold to your stage base
- on the small end epoxy in a 20mm diameter chrome steel ball (with the combo I use only a fraction (<25% ?) of the ball actually enters the top of the tube
- find yourself a disk magnet with a countersunk mounting hole http://www.supermagnete.be/eng/CSN-16
- stick a lump of cork or whatever to the flat side of the countersunk disk
- the countersink on the reverse side then holds on the ball
- the whole assembly then holds to the plate on your stage.

This lot together gives you an adjustable/removable mini ballhead mount which lets you adjust in all axes over almost an entire hemisphere, and if you use strong enough magnets seems vibration free. A picture is worth a thousand words but hopefully you get the idea.
rgds, Andrew

"Is that an accurate dictionary ? Charlie Eppes

AndrewC
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Post by AndrewC »

.. one other idea if you want to add mass to a base like this is to get some Tungsten and route out a recess in the base and fix it in. Tungsten because it is much denser than iron.

In the States you're spoilt for getting it:

ebay: 170347822378

Myself, I bought machine grade rods from a Russian gentleman which I just force fitted into some holes drilled in my wooden base.

Andrew
rgds, Andrew

"Is that an accurate dictionary ? Charlie Eppes

RogelioMoreno
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Post by RogelioMoreno »

Charles,

Very interesting, thanks for sharing.

Rogelio

enricosavazzi
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Post by enricosavazzi »

Charles,

[warning: some semi-serious text follows]

this is a nice equipment, but, as you have found, portability and stability are not easy to obtain together. Some time ago I sat down to think about solutions along similar lines.

Mass absorbs vibration, so my first thought was incorporating the photographer's mass into the equipment (since it gets transported to the destination "for free" in any case). However, this was not a promising solution, since it would be impractical to stop moving, breathing etc. (not to mention heartbeat and physiological tremor) to achieve a sufficient "stillness", while still carrying out photography.

My second thought was using some mass locally available. The easiest to get would probably be water. A tank built into the base of the stand would certainly work. On the other hand, the base of the stand could be built as a box, like some "travel copy stands" or "travel photographic enlargers" of the past, which were made like suitcases containing the rest of the disassembled equipment. In this way, any unused equipment would contribute to the mass. Alternatively, this space could be filled with phone directories, motel Bibles, motivational self-help books etc. to increase the mass. Equally effective, and less likely than water to leak out.

I also gave some thought to the construction of the vertical column. A mostly hollow aluminium profile of wide section area (there is 90 by 90 mm, for instance, and perhaps even more) would perhaps be stiffer and less likely to vibrate than a solid column of the same mass but thinner section (any engineer might be able to comment on this). A hollow column might also be filled with a sand-bag (or a water-filled balloon?) to absorb vibration. Its internal space might even be useful to store the lenses and other small items for transportation.

In more practical terms, I started with an idea similar to your stand and worked my way to better stability by reducing the distance and number of joints between the bellows and column. The first thing to go was the base of the Nikon PB-6 bellows. I took it off the rail, took out the geared rod at the bottom of the rail and drilled and tapped two 1/4 tripod attachment sockets there. The bellows can easily be restored to its original function if necessary. Next was the system of quick-release plates at the back of the coarse/fine focuser, which I attached directly to the column. I still have a quick-release plate and socket between focuser and bellows, which could be taken out to make the construction even stiffer. I kept it as the only remaining way to change the height of the bellows above the base of the stand, but perhaps the two bellows standards would be enough for this. My use of a combined coarse and fine focuser further eliminates one joint (actually three joints, counting the quick release plate and socket between your fine and coarse focuser). The total distance between optical axis of the lens and column shrunk by about 10 cm in the process.

The improvement was quite noticeable in my case. I further reduced ambient vibration by attaching the largest Sorbothane feet I was able to find at the bottom of the base (5 cm hemispheres work best for me). A theoretical possibility that I might test in the future is of using a two-stage Sorbothane damper (a second plate with its own set of Sorbothan feet, placed under the base and Sorbothane feet of the stand). My thinking is that this second stage would likely have a different resonant frequency, thus further reducing the transmission of vibration.
--ES

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Post by AndrewC »

enricosavazzi wrote:... I further reduced ambient vibration by attaching the largest Sorbothane feet I was able to find at the bottom of the base (5 cm hemispheres work best for me)....
That doesn't always make sense. For viscoelastic materials to work "properly" you have to match the load, forces and size of damper. Bigger isn't always better - if it is underloaded it will oscillate.
rgds, Andrew

"Is that an accurate dictionary ? Charlie Eppes

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Post by ChrisR »

Great post Charles, I keep returning to it.
Vibration - did you use flash for illumination?

ANdrew - ummm
I had to look up loc-line..
mauve = magnet, yellow = goo ..??
Image

How about using two holy magnets, lower one inverted - screwed down to something, even :?
Image

Charles Krebs
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Post by Charles Krebs »

:D
Gotta love it! No lack of ideas here. There seems to be a universal trait among this "core" group... get a piece of gear, or see some set-up and immediately try to figure out how it could be better.

Naturally I've done the same with my own "rig". :wink:

Some constraints in assembling this were time, and thus the need to use pieces from the existing "parts" boxes. For this set-up I did have to buy the maple base, but that's about it. (A local hardwood supplier had this piece sitting on his "scrap" table... I didn't even have to cut it!).

My old darkroom (where I now work at home) has a concrete floor directly on the ground. Quiet neighborhood, and no more kids running around the house. So when I use this at home, despite it's "shortcomings" there is really no problem. But just in principle, I don't care for the large "overhang". And it certainly does not help in a less stable environment. So there are a few ways I’ve contemplated changing things…

Use one of my microscope focus blocks on the baseboard for the “Z” adjustment and eliminate the Velmex. I could even eliminate the base of the bellows and bolt a long Arca style plate directly to the rail of the bellows. That would eliminate a huge amount of the "overhang". (I would then be going directly from the 60mm AS clamp on the post to the bellows rail. A 60mm AS clamp makes an incredibly solid and strong connection). The finer movement of the focus block would also allow me to make better use of the 20X (and up). The pitch on the lead-screw of the Velmex slide I used here is “doable” for 10X, but at 20X gets very “iffy”. I actually have a larger Velmex with a finer lead-screw, but at 20X I would prefer to use a different base anyway. I like the “ball/socket base” shown here very much up to about 10X, but over that it is nice to have some sort of x/y control to position the subject instead of manually sliding the base unit. So I envision an Olympus BHMJ block with a stage such as eBay 120561186690 or eBay 200464611561 attached to an “L” bracket that’s fastened to the plate on the focus block that moves. This would mean more careful subject preparation since I would lose the ability to tilt the subject as I can with the ball/socket base shown here. (But there are always ways… :-k :wink: )

My personal taste would be to never eliminate the ability to easily rotate the camera body. Sometimes it takes awhile to get the subject as parallel as possible, or even to get it "framed" in the viewfinder. Then before I shoot, for composition reasons, I realize I would like a slight "rotation". I hate messing around with the subject at that point. (And there is a fair number of times when I'll do both a "vertical" and "horizontal" shot... which I realize sounds weird since you're looking straight down! ). So I would stick with a bellows that allows this. Since the overhang would be so greatly reduced, I would be less concerned about the bellows weight. I would actually use an old Exacta bellows (see picture). This is similar to this Pentax in many ways... even uses the same rail… but it is much heavier and locks down more solidly than any bellows I have ever seen. The Pentax shown above is cast metal, but “hollowed” (don’t know the correct term). The Pentax standards lock via a fairly short single point on the locking side. The Exacta bellows are solid cast. The base clamps along a full 100mm length. Both standards use a “split” design that, when tightened, pulls the metal together along a 50mm length of the rail. No plastic dovetails... all metal to metal. When this thing is locked down it is solid! The only real downside is that the standards are not gear driven, and the base gearing is rather crude compared to newer Japanese bellows. But used on a stand like this the finer movements are done with other mechanisms, so it doesn’t bother me at all. (I should mention that I think there may be some versions of this bellows that were made without the rotating camera mount, so if that's a feature you want and you start looking for these be sure to check that out).

Image

One other thing I like about bellows is that if you keep the front standard all the way down and extend via the back it require a minimum amount of refocusing, and the chances of smashing the lens into the subject is lessened. With the Canon 65MPE used vertically, or with the Olympus variable tube, the front lens components move forward large amounts as magnifications are increased. So you always need to be cautious and usually adjust an elevation control whenever you significantly change magnifications so you don't hit the subject with the lens.

Also, a word on the spreadsheet I referenced. Keep in mind that the three lenses I used have a pupillary magnification factor of (or extremely close to) “1” which keeps the formulas simpler. A COC of 0.019 was used (22.3 x 14.9 mm sensor) and my cut-off for “green” was an effective f22, and the cutoff for “yellow” was f32. This was good for my purposes this time, but if the goal were a very large print or some heavy duty pixel-peeping these cutoff effective apertures are too small and should be modified. But the basic format and color coding works quite well in an environment where there are likely to be distractions.

Chris
Vibration - did you use flash for illumination?
Actually I used two LED panels that video folks use on their cameras. These were very nice, high-end pieces and worked quite well. They cost more than I would want to spend but I might take a second look at some of the eBay "cheapies". The vibration at 20X was really not that noticeable on the (external, HD) screen when viewed full frame, but magnified 10X it got scary!

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Post by ChrisR »

So I envision an Olympus BHMJ block with a stage such as eBay 120561186690 or eBay 200464611561 attached to an “L” bracket that’s fastened to the plate on the focus block that moves.
That sounds awfully like a microscope!

I have an old Vickers (£15) whose head I've bored a hole through. I took a Chinese Nikon tube, & added a Nik-39mm adapter with 39mm tubes in. That makes a shoulder which sits on the flat top surface of the head. The 39mm dangles through, and the original thumb-screw holds it. 42mm would have been better. It works but the focus block isn't great. A part CH would make a good start. One day I'll take a Hilti to one...
For low mags there are of course 2x (and I think even 1x?) objectives.

Charles Krebs
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Post by Charles Krebs »

Yeah it does. I'll probably just remove the bellows base and put a long AS plate on the bellows rail. Use it for 10X and less with the enlarging lenses and the 10/0.21. It really worked well for that.

I've got another project that I may tackle next. I want set up a microscope for "direct projection" with the 5, 10, 20 and 40 CF M Plans on the nosepiece. I've actually got the ability now if I remove the head (as you described and as Rik has done), but what I really want to do is incorporate an old trinocular head I bought just for this purpose. I want to modify the head so that I can get a clean shot (ie. no glass at all) in one of the slider positions. The reason I want the trinoc is because at 20X and 40X it's really nice to be able to view through eyepieces to examine and explore the subject in order to pick the best photo situations. As nice as it is to have the camera view fed into a HD monitor, I still find it easier and more enjoyable to explore using visual eyepieces. Don't know how it will work out, but I've had this head sitting in a box for a couple years now so it is probably time to give it a try.

enricosavazzi
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Post by enricosavazzi »

Charles Krebs wrote: ...
what I really want to do is incorporate an old trinocular head I bought just for this purpose. I want to modify the head so that I can get a clean shot (ie. no glass at all) in one of the slider positions.
...
I did this a couple of weeks ago, with a Nikon Labophot head (which, incidentally, does remove the beam splitter from the optical path in photo mode). I also shortened the photo tube for direct projection (no photo eyepiece). It works fine with an APS-C sensor, but it might vignette on a full-frame sensor (which I don't have). This modification was made tricky by the already very short photo tube and two lens groups in the optical path to the observation eyepieces. Solution: lengthen the optical path to the eyepieces by removing the lenses and inserting a 10 mm spacer between main body and binoviewer.

I also removed the prism from a Zeiss Photomic (corresponding to the 100% light to camera tube) for direct projection. Also this was successful.

I even modified a Wild/Leica M420 for direct projection, but in this case the beam splitter is fixed. I also modified this scope to carry ordinary photomacrographic lenses on a revolving nosepiece.

All the above work well. Precision focusing through the observation eyepieces and reticle is child's play compared to focusing through the optical viewfinder of a DSLR. Framing must still be done with the camera viewfinder or live view, because the observation eyepieces only show an image circle of 18-20 mm instead of the 30 mm necessary to cover an APS-C sensor (the mismatch gets lesser with a Four Thirds sensor). I have been considering astronomical eyepieces with 2" barrels and a field stop close to 50 mm, but a trinoviewer for these is not going to be cheap.

The main drawback of the modified trinocular head is that it adds 110-150 mm to the optical path, so you cannot use it at low magnification (but then again, you don't need it at low magnification, either).

In general, I found that all photomacrographic lenses I tested (dozens of the common ones including Luminar, Photar and Macro-Nikkor) display quite a bit of axial chromatic aberration in out-of-focus areas of the subject (while correcting it well in in-focus areas). A beam splitter does introduce both axial and radial chromatic aberration, but less than a photomacrographic lens. So you might want to test with the beam splitter in place before taking it out - it might work well enough after all.
--ES

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