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Old February 4th, 2011, 05:05 PM   #1
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zoom vs variable interaxial

I've been watching hours of video from my dual camcorder rig and a thought occurred to me.
My camcorders have 15 power zoom which causes major window violations and major eye strain when going from min to max zoom.
I have been fixing this in post but it's a hassle.
I wonder if my controller were to adjust the interaxial spacing in combination with zooming if that could solve this issue.
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Old February 4th, 2011, 05:27 PM   #2
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Yes. On automated rigs we tend to decrease the interaxial as we zoom because the magnification causes larger and larger divergence in the background. However, you should consider the object-flattening effect caused by longer focal lengths when choosing to zoom.
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Old February 4th, 2011, 05:48 PM   #3
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How about a combination of variable zoom,interaxial and toe in?
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Old February 4th, 2011, 08:56 PM   #4
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How about thinking about moving the camera instead of zooming? With proper follow focus I've found this to be the best solution of all. Zooming introduces way too many problems from lens divergences to cardboarding.
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Old February 4th, 2011, 09:17 PM   #5
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What I am basically trying to do is operate the camera for wildlife monitoring by remote control.
I am already doing this successfully except for the above problem.
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Old February 4th, 2011, 09:34 PM   #6
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It should be possible to move the interaxial servo motor and toe motor together with the LANC controlled zoom to maintain the proper parallax should it not?
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Old February 5th, 2011, 06:16 AM   #7
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I am beginning to see that in order to maintain proper perspective from main to max zoom, I would have to increase the IA and TI proportionally with zoom.
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Old February 5th, 2011, 10:03 AM   #8
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I know that you are using consumer cameras, but you probably need to built a rig with the similar capabilities as Cameron did here: YouTube - Avatar's Cameron-Pace 3D Camera Rig Review . He can control everything remotely, which can be fairly easily done with wifi these days (or RC model controllers). Otherwise, since you don't need to be portable, you seem to need a remote controlled scaled down Hurricane rig.
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Old February 5th, 2011, 10:24 AM   #9
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I did some experiments this morning and have discovered that all I need to do to obtain satisfactory results is toe in the cameras in sync with the zoom. I already have a servo controlled toe in and I was using that but can't synchronize them with my current method.
This will definitely get incorporated into my new controller.
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Old February 5th, 2011, 11:57 AM   #10
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I did no looking into this at all, but I know that RC helicopter controllers can combine several axes with one control motion. Maybe there is some blending useful for your need. Of course you cannot zoom while shooting and get really good results. You must zoom - setup - shoot. The optics generally "dances" all over the place throughout the zoom range. This was discussed on this forum in fair detail in the past.
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Old February 5th, 2011, 01:04 PM   #11
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"Of course you cannot zoom while shooting and get really good results."
I'm going to try it anyway but thanks for the info.
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Old February 6th, 2011, 10:04 AM   #12
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Pavel is correct. There's a couple of problems when you zoom using consumer cameras with build in zooms.

First, they may not zoom at the same speed- they're not built to that type of precise tolerance.

Second, the optical center of the lens will change as you zoom.

Third, you'll need to adjust your alignment in post, probably using several keyframes through the zoom.

But I encourage you to try it, even if you only learn that you don't want to do it anymore!
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Old February 6th, 2011, 10:34 AM   #13
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Pavel is correct. There's a couple of problems when you zoom using consumer cameras with build in zooms.

"First, they may not zoom at the same speed- they're not built to that type of precise tolerance.

Second, the optical center of the lens will change as you zoom.

Third, you'll need to adjust your alignment in post, probably using several keyframes through the zoom.

But I encourage you to try it, even if you only learn that you don't want to do it anymore! "
Thanks for the feedback."


A short explanation of what I am doing might be in order.
I have experimented with several different camcorders and finally settled on the Canon HF21s. They have problems with sync which I am able to work around for the most part.
I have done numerous tests with zooming in and out and am having excellent results. I have obtained virtually perfect alignment throughout the zoom range of fifteen to one.
I am controlling and monitoring the cameras in a somewhat unique way. I am viewing the live 3D video in a window on my desktop computer using the checkerboard mode of my 3DTV.
The live 3D video is of surprisingly good quality.
I will put some samples on line and let you all see for yourself soon.
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Old February 8th, 2011, 02:14 PM   #14
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There are people spending 100's of thousands of dollars on matched zooms, motorised rigs and controllers that still end up having to correct dynamically with something like the Sony MPE200 3D processor or in post production. It is extremely difficult to get any two lenses to track correctly without shifting the optical axis. You might get away with it on a small window, but on a big screen it's a different matter.

To elaborate on what Tim said even if you get the electronic and mechanical parts all in perfect sync there is still the problem that a stereoscopic zoom sends two conflicting messages to the brain. Two dimensionally, as you increase focal length you foreshorten the image, that is to say the near and far objects within the scene appear to get closer together, and all objects appear to move closer to the viewer. At the same time the magnification of the image increases the disparity (left/right difference) between those same objects, so stereoscopically they all appear to move away from the viewer and away from each other. This is a serious conflict for the brain, one message, the scale depth cue says everything is getting closer while the stereoscopic cue says everything is moving further away.

You can mitigate this by decreasing the interaxial in sync with the increase in focal length, but now your image becomes flatter and less rounded as the focal length changes, which is again an un-natural effect and objects appear to become a series of flat cutouts at differing depths.

Long focal lengths and S3D are very difficult to get to work right, without cardboarding or scale issues. Zooms even harder to make convincing.

Good luck with your experiments!
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Old February 9th, 2011, 10:45 AM   #15
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Thanks very much for the information. It might prove helpful.
Let me point out that I had cataract surgery on both eyes years ago
and can't focus, in addition to retina surgery on both eyes.
Therefore I'm not qualified to judge the quality.
I have my grandson for that.
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