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Consultation: stereo microscope stand for photomacrography
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ChrisR
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Joined: 14 Mar 2009
Posts: 6597
Location: Near London, UK

PostPosted: Fri Aug 07, 2015 11:13 pm    Post subject: Reply with quote

If you're only using flash then I don't think it matters much. If the image moves between exposures the software will align them to the nearest pixel - here I must
refer to Rik. The focus step will always move things a small amount unless the optic's telecentric. If you're using more pixels than the lens can resolve, which is often the case, then I'd doubt the shift would have a visible effect in the output.

Rik Question
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rjlittlefield
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Joined: 01 Aug 2006
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Location: Richland, Washington State, USA

PostPosted: Mon Aug 10, 2015 11:08 pm    Post subject: Reply with quote

ChrisR wrote:
If you're only using flash then I don't think it matters much. If the image moves between exposures the software will align them to the nearest pixel - here I must
refer to Rik. The focus step will always move things a small amount unless the optic's telecentric. If you're using more pixels than the lens can resolve, which is often the case, then I'd doubt the shift would have a visible effect in the output.

Rik Question

The alignment is good to some small fraction of a pixel. I vaguely remember testing it down to 1/16 pixel or so, using deliberately perturbed images, when I was doing the code development. The issue has seldom come up since then, and I can't say exactly how good it is. It's probably sufficient to say that nobody has sent me anything that prompted me to try making it even better.

Reviewing this now 4-page thread, I see that I have not yet provided any general comments.

Overall, I think my sympathies lie more in line with ChrisR's concerns that the problem is being overworked.

It seems to me that what matters in the end is only how good the images are, and how hard you had to struggle to create them.

In my own experiences, I've found that even frighteningly flimsy setups produce good results when I either a) illuminate with flash, or b) kill environmental vibrations and expose with EFSC after a suitable settling time.

That does not mean that "frighteningly flimsy" setups are desirable in any sense. If they're flimsy enough, then it can become a challenge to even set up the desired framing and focus limits. Clearly that's a bad thing.

However, once the setup has become stable enough that it's simple to work with, I think you've reached the point where further effort is probably wasted.

Even if you build a massive baseboard and column, and fasten everything with multiple large clamps, you're still left with that relatively small and obviously movable connection that we call a focus block or rail. I guarantee to you that that thing is going to flex noticeably if any force is applied.

All the other parts of your setup are going to flex also, probably a lot more than you expect. I am reminded of a recent experience that I documented as follows:
rjlittlefield wrote:
At this particular moment I have reorganized my equipment into a horizontal setup that is built on a Newport TD-12 optical breadboard sitting on SA2-FT Sorbothane feet, with the specimen positioning stack fastened to a Newport Model 70 optical rod (1.5 inch diameter) that is bolted to the breadboard. As seen in Live View, touching the camera makes the image move. Touching the specimen positioning controls also makes the image move. Touching the body of the focus block makes the image move. Touching any part of the optical rod makes the image move. For that matter, touching any corner of the breadboard makes the image move, and by "touching" I mean light fingertip pressure like typing a key on a keyboard.

These effects are most obviously seen when the pressure is a shock, because then the image vibrates for a little while.

But there is an easily detectable and stable shift of the image depending on whether a roughly 4" section of M42 tubes that weighs only 106 grams is or is not sitting on one corner of the breadboard.(!) This surely represents a tiny bit of flexibility in the breadboard, magnified by lever arms due to elevated equipment that is mounted at different points on the breadboard, further magnified by lenses and tiny photosites that take 0.4 micron of physical displacement between subject and lens, and turns that into a full pixel at 10X.

However, none of that matters one whit as long as the flex is not large enough to interfere with framing and focusing. I would expect that any of the proposals mentioned in this thread would meet that criterion.

Finally, I am struck by Charles Krebs's follow-up to my report in that other thread. It is small enough to reproduce here.
Charles Krebs wrote:
I am enjoying this little "set-up" side discussion.

First aspect... search out all possible locations of movement, and, within reason, remedy them.

The reason I say "within reason" is because I'm convinced that no matter what you do, a versatile set-up that will allow you to work effectively with a variety of optics, subjects, and lighting arrangements will show some motion when you touch it as Rik has described. This certainly does not imply that you should not work toward the most stable arrangement possible, but sometimes very useful versatility features might require some additional connections and components that could potentially be a source of minute flexure.

The second aspect that comes to mind is that no matter how obsessive you are with the hardware set up, you must use shooting techniques that eliminate those last vestiges of vibration. I really have sympathy for some folks that live in places where they need to deal with constant external environmental causes of vibration... this is tough. But I think the majority of us work in places where we can avoid environmental causes of vibration. It may mean turning off the washer/'dryer, or working at times when other household members are not running around upstairs. I've created equipment arrangements that, in retrospect, looked as if movement might be a nightmarish problem, and also set-ups that were extraordinarily stable. As long as the appropriate shooting techniques were used they were all fine and yielded excellent results.

I hope this helps.

--Rik
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