Re: Flat pan or circular pan? #capturing #howto #alignment


Bob Aldridge
 

You are right about toeing in causing difficult in viewing different distances. And it is a subject that has been debated for many years. A Stereoscopic Society Bulletin from 1964 has an article on the subject from "The Professor" (Bill Dalgoutte) referring back to the British Journal of Photography in 1904 which said that there was no advantage in toeing in. He then alludes to "a popular post-war textbook" that claims that toeing in is natural, because our eyes do it...

The Professor then goes on for the rest of the article explaining why toeing in will render objects at different distances from the one that is toed in to will be progressively more difficult to view...

Another article in a 1969 Bulletin seems to defend E.F. Linssen in his book "Stereo Photography in Practice" (which would appear to be the "textbook" that the Professor mentions) and his view that toeing in is natural... Interestingly, the author of this article is not named, but it seems to be someone with a problem with Bill Dalgoutte - the then Editor of the Bulletin and the "Honorary General Secretary" of The Stereoscopic Society, and also "The Professor" (Collectively known as "The Tolworth Triumvirate" since Dalgoutte lived in a suburb of London called Tolworth...) My guess would be John Singleton, but that is just a guess...

It is interesting that another article in the same Bulletin immediately follows with the title "The mathematical analysis of toe-in distortion" counters it with a demonstration of why toeing in is bad! It is also unattributed, but an allusion to "the books in the library of the Hon Gen Secretary (Bill Dalgoutte, AKA The Professor) would suggest that he was the author...

Anyway, I, personally, think that you can "get away" with mild toeing in, but it is not ideal. And the detrimental effects will be worse the more "depth" there is in the scene. Many of the distortions can be "corrected" in the digital world, of course, which was not the case in the 1960s, but there will always be some negative impact on the final image.

So I start wondering why toeing in would be desirable. For cameras with "normal" lens spacing, taking images of subjects between about 2 metres and infinity, the only benefit is to avoid cropping opposite sides to set the "window", but todays high resolution cameras yield images that reduce the quality impact of that cropping...

But, for close-up photography, it is a different story. If you cannot get the lenses close enough together, it is possible that one camera will not even see the main subject! Here, toeing in MIGHT be an answer. But it will be vital to seriously control the depth in the scene. If you don't you could easily get totally different backgrounds! A better approach might be to use telephoto lenses so the camera is much further from the subject obviating the need to toe-in. But, again, the depth in the scene must be controlled or the effect that Arthur Girling called "Reverse Frustrum Distortion" will become evident!

As with EVERYTHING in stereoscopy, there are compromises. And that is why it is so fascinating.

Just for the record, I believe that the ideal is to keep both sensors in the same plane. and that means that toeing in should be avoided without a very good reason to do it... It should not be used to set the window, for instance.

Bob Aldridge



On 29/01/2021 01:07, David B via groups.io wrote:
 I have used two methods of camera positioning for the stereo images.  One is to choose a focal point and point the camera straight at that point for each of the two images (camera moves on a radius around the focal point).  The other is to flat pan the camera so that the center of the image is offset between the left and right.

I am wondering which is better.

It seems for the best view when focused on a single point would be the circular motion because it is more like the natural geometry of the human eyes.  Where this may be worse is when you shift your attention through the image on locations that are not a this focal point.  Then it can be less natural?

Maybe for best viewing of other points throughout the image a flat pan is better?

It seems the closer the object the more effect there is for these choices.

How do you do it and what works best?  When doing close up shots what do you do?

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