Can you make stereo pairs by rotating the subject?

[Beatsy]

It seems logical that taking two stacks with the object rotated a few degrees around the y axis in one of them should create the equivalent of a view from each eye - a stereo pair. Might be some wrinkles if lighting doesn't rotate with the subject, but flat diffuse light from all around should be OK. I thoiught...

I was going to just ask the question in the title, but I decided not to be a lazy beggar and had a go - even though I could just be "rediscovering" something that everyone and his uncle have been fully aware of for centuries. That happens a lot to me...

I used a manky old butterfly foot that was already on the rig and shot with a 50x Mitty on a 135mm tube lens for 33x onto the sensor. FF Sony A7r2 running in APS-C crop mode (18 megapixels) with around 200 images per stack (nominally 1 micron steps).

First, a straightforward stack. Flat lighting, no retouching, and the stack didn't go all the way through. Enough "sticky-out" details to detect a stereo effect if it works though



I figured it would be worth creating a baseline stereo to compare against (and if I didn't, one of you would ask for it) and created a stereo from the image above using Zerene. I used +4 and -4 offsets. Worked as expected.



Then I rotated the subject 4 degrees and took another stack. Well, I meant to rotate it 4 degrees, but as well as rotating, it lurched left and seemed to tip sideways and forwards a bit too. My rotation stage is very scratchy and coarse - not really designed for such fine control. Anyway, I left it as it was and stacked it again.



So now it was time to see if I had a working stereo pair, but I was sure it was doomed as the "lurch" would have messed it up. Did it work? You be the judge...



One big benefit, despite appearances, is that this method can use fewer images in total (less than half as many in each stack) to generate good stereo results for screen resolution output. Zerene's stereo algorithm starts to get "artifact rich" if the stack is too sparse. Encouraging...

[rjlittlefield]

I could just be "rediscovering" something

Just so!

The "true stereo" technique that you're experimenting with is the classic method that used to be the only method. I shot many of them in the old days.

It definitely can have the advantage of fewer artifacts, especially at lower magnifications and smaller NA's where stacks are short.

Disadvantages, as you've discovered, are that that you have to shoot two stacks with consistent lighting and framing. You also have to choose portrait/landscape orientation and stereo separation at the time you shoot the stacks, no adjustments afterward.

One big benefit, despite appearances, is that this method can use fewer images in total (less than half as many in each stack) to generate good stereo results for screen resolution output.

That's a very interesting comment, and I have to say, I'm not convinced that it's correct.

In my own experience, especially at higher magnifications, the comparison has gone the other way 'round. Both stacks of the true stereo method have had to be shot at the same step size, to avoid focus banding. So, it's been at least double the frame count and more than double the trouble. The reason I say "at least" double the frame count is that with true stereo I've had to shoot deeper stacks to avoid a form of "focus disparity" in which features near the back of the subject would be sharp in one view but blurred in the other. This problem becomes worse with shallower subjects; crystals on microscope slides are an extreme example.

It seems that your experiences have been different from mine, at least to this point, so I will be interested to see how your study progresses.

--Rik

[Beatsy]

One big benefit, despite appearances, is that this method can use fewer images in total (less than half as many in each stack) to generate good stereo results for screen resolution output.

That's a very interesting comment, and I have to say, I'm not convinced that it's correct.

I just knew I'd get in trouble for that

Wholly based on my experiences with the (not very many) stereos I've made. I *always* got better stereo results with more (too many) images in the stack. Sometimes not good enough to keep - but always better than with a "gappy" stack. Having said that, I think most of my stereos have been pretty high mag - so I've not experienced the full gamut and accept I'm very likely wrong in principle - but (my) practice to date has definitely been as I said.

[rjlittlefield]

Probably there are some complicated tradeoffs. That seems to be the usual case.

Synthetic stereo is particularly vulnerable to sideways streaking around small specular highlights. I think of them as "sparkly streakies". The severity of those varies a lot depending on subject and illumination. The same problem, though less severe, also occurs in single stacks, so I've gotten in the habit of using quite flat illumination that minimizes the difficulty.

I would be very interested to hear more about your practices. My own history is that I've always loved stereo, but hated shooting them, even after building a setup that made rotating the camera around the subject pretty simple. So when synthetic stereo got good, even for difficult subjects like bristly bugs, I simply gave up shooting true stereos for macro/micro and switched to synthetics. I won't be going back.

Since your experiences are different, it would be nice to have them documented in enough detail for other people to make an informed judgement about when to use each technique.

--Rik

[Smokedaddy]

A guy I correspond with, Tom Wagner, creates lots of stereo images and they are outstanding. He has a Facebook page along with instructions. He found an animation of a rotating COVID-19 virus and after making two screen captures, made it into a cross-eyed stereo image.

https://www.facebook.com/notes/tom-wagn ... 976240242/



-JW:

[kds315*]

Not outstanding at all, use stereophotomaker to adjust at least the stereo basics as my eyes hurt to see it...what were you smoking btw.?? ;-)

[Smokedaddy]

... it works perfect for me. i rarely do cross-eyed stereo viewing. He does use SM. It takes a while for my eyes to adjust but this one looks outstanding 'to me' as well.



-JW:

[ChrisR]

... it works perfect for me.

Me too, I must say.
The DNA model works, but that's a bit hard in the eyes for me.

[Smokedaddy]

... not for me. <g> I wonder why? I see a HUGE DOF, probably only takes a second and it doesn't bother me.

[kds315*]

The DNA model however works very well for me, too!

[rjlittlefield]

Both work fine for me.

I have tried to identify some technical defect in the stereo for the coronavirus, for example some vertical disparity caused by axis of rotation not vertical. But everything I check looks fine.

I wonder if Enrico is having trouble because the image is not very sharp?

--Rik