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Subject: Rotating film chips - how far can you go
Date: 2017-05-18 14:19:25
From: coronet3d

Most of the time I mount, I end up rotating my film chips slightly to get a "straight" image, however I just got a roll back where I've a more substantial tilt of the image ~15 degrees or more.  I was just wondering how far could I go with adjusting for tilt of the camera in mounting.  Could I perahaps go as far as 45 degrees (with the appropriate cropping).  Has anyone done that?

Thanks,

Steve

Subject: Re: Rotating film chips - how far can you go
Date: 2017-05-18 17:34:15
From: Timo Puhakka2
What camera are we talking about? I don't see how you can get 15 degrees of misalignment unless you are talking about cha cha or a twin rig. In any case, you should be able to rotate a fair bit, but only experimentation will tell. 45 degrees, I doubt it.

Timo

On 18-May-17, at 4:19 PM, coronet3d@yahoo.com [MF3D-group] wrote:

 

Most of the time I mount, I end up rotating my film chips slightly to get a "straight" image, however I just got a roll back where I've a more substantial tilt of the image ~15 degrees or more.  I was just wondering how far could I go with adjusting for tilt of the camera in mounting.  Could I perahaps go as far as 45 degrees (with the appropriate cropping).  Has anyone done that?

Thanks,

Steve



Subject: Re: Rotating film chips - how far can you go
Date: 2017-05-18 18:06:32
From: George Themelis
Think of the stereoscopic deviation as a vector. When the image is correctly aligned, this vector is entirely along the x-direction (line of eyes, bottom of mount).
 
When you rotate, this vector starts having a component in the y-direction (perpendicular to the eyes). This is pure error (vertical misalignment).
 
The question is, how large is this error and can be tolerated?
 
The magnitude of this error is: D x Sinφ (D is the deviation, φ is the rotation angle).
So the error is proportional to the deviation and the angle of rotation.
 
If the picture is flat (D = 0) clearly there is no error. You can rotate a flat picture as much as you like, you do not get any viewing error (vertical misalignment). The more depth the picture has, the larger the error. Also, the larger the rotation angle, the larger the error.
 
sin05 = 0.09
sin10 = 0.17
sin15 = 0.26
sin25 = 0.42
sin45 = 0.71
sin90 = 1.00
 
I don’t think you should rotate more than 5 degrees. Even this is stretching it if your picture has a good amount of depth.
 
At 15 degrees, 1/4 of the total deviation is projected in the wrong direction and becomes an error.
 
At 45 degrees, almost 3/4 of the deviation is an error. This could be a disaster.
 
At 90 degrees the picture has no depth (no deviation in the x-direction) and the entire deviation has become a vertical error. So don’t turn the camera 90 degrees and then expect to rotate the film chips by 90 degrees to “align the horizon.”
 
But, again, it depends on the total deviation. If you take flat pictures, feel free to rotate as much as you want :)
 
George
 
Sent: Thursday, May 18, 2017 4:19 PM
Subject: [MF3D-group] Rotating film chips - how far can you go
 
 

Most of the time I mount, I end up rotating my film chips slightly to get a "straight" image, however I just got a roll back where I've a more substantial tilt of the image ~15 degrees or more.  I was just wondering how far could I go with adjusting for tilt of the camera in mounting.  Could I perahaps go as far as 45 degrees (with the appropriate cropping).  Has anyone done that?

Thanks,

Steve

Subject: Re: Rotating film chips - how far can you go
Date: 2017-05-18 21:07:42
From: George Themelis
I think it is a matter of technique than camera. The way I understood the question is rotating the film chips to straighten the horizon. If you tilt the camera as you take a picture, the horizon will be tilted but the image is still perfectly aligned. If you rotate the film chips to align the horizon, you will end up misaligning the image. The urge to straighten the horizon is physiological and strong in stereo viewing.
 
George
 
 
Sent: Thursday, May 18, 2017 7:34 PM
Subject: Re: [MF3D-group] Rotating film chips - how far can you go
 
 

What camera are we talking about? I don't see how you can get 15 degrees of misalignment unless you are talking about cha cha or a twin rig. In any case, you should be able to rotate a fair bit, but only experimentation will tell. 45 degrees, I doubt it.

 
Timo
 
On 18-May-17, at 4:19 PM, coronet3d@yahoo.com [MF3D-group] wrote:

 
 

Most of the time I mount, I end up rotating my film chips slightly to get a "straight" image, however I just got a roll back where I've a more substantial tilt of the image ~15 degrees or more.  I was just wondering how far could I go with adjusting for tilt of the camera in mounting.  Could I perahaps go as far as 45 degrees (with the appropriate cropping).  Has anyone done that?

Thanks,

Steve

 
 
Subject: Re: Rotating film chips - how far can you go
Date: 2017-05-18 21:37:06
From: Brian Reynolds
coronet3d@yahoo.com [MF3D-group] wrote:
>
> Most of the time I mount, I end up rotating my film chips slightly
> to get a "straight" image, however I just got a roll back where I've
> a more substantial tilt of the image ~15 degrees or more.

As others have mentioned, it is much better to get it right when you
take the photo. If you rotate the film chips when mounting, you will
also have to realign them vertically, as George mentioned.

I don't know what camera(s) you are using. On my Sputnik I mount a
bullseye level on the top right deck. While framing the photo with
the waist level finder I can check the level to make sure the camera
is straight both left/right and fore/aft. I can also observe the
bubble, if it is jiggling I know that I'm not holding the camera
steady enough, and I should wait until it settles down.

--
Brian Reynolds | "It's just like flying a spaceship.
reynolds@panix.com | You push some buttons and see
https://www.panix.com/~reynolds/ | what happens." -- Zapp Brannigan
NAR# 54438 |
Subject: Re: Rotating film chips - how far can you go
Date: 2017-05-23 14:58:39
From: coronet3d

Dr. T's mathematical analysis has me thinking.  The only way to test it out would be to shoot with twinned cameras.  I know that Lipton was in favor of stereo discrepancies for artistic purpose.  I'd like to see with my eyes what it looks like to foul-up the image by "correcting" tilt by rotating the film chips.

Steve

Subject: Re: Rotating film chips - how far can you go
Date: 2017-05-23 21:53:31
From: borisstarosta
When you tilt your stereo camera or rig, then correct for the tilt in mounting, you will introduce vertical parallax all over the image (i.e. eye-strain) and reduce horizontal parallax (i.e. 3d effect).  In my experience, you can get away with about five degrees of tilt, but beyond that you'll start noticing something unpleasant in the viewing of image details.

But I'll admit I've never tested the limits of this - I'd be curious to hear your results!

This also depends on how much depth you are actually capturing... or by corollary, how much stereobase you are using.  If your view is mostly flat, you'll be able to get away with more tilt, probably.

––––
Contemporary work in the Stereoscopic Arts:  www.patreon.com/retroformat
––––

Science is the belief in the ignorance of expertsRichard Feynman
Subject: Re: Rotating film chips - how far can you go
Date: 2017-05-24 06:05:54
From: George Themelis
If you want to see what happens when you rotate the film chips you can just rotate any pair that you have now.  
 
Consider the extreme: If you rotate the film ships by 90 degrees and try to view the pair, this pair will have no stereoscopic deviation in the horizontal (viewing) direction, so it will have no depth, and all the deviations will be in the vertical direction (vertical error).  So, as you rotate, it is gradual process where you lose depth and gain headache (or whatever effect vertical misalignment has on you).
 
George
 
Sent: Tuesday, May 23, 2017 2:43 PM
Subject: Re: [MF3D-group] Rotating film chips - how far can you go
 
 

Dr. T's mathematical analysis has me thinking.  The only way to test it out would be to shoot with twinned cameras.  I know that Lipton was in favor of stereo discrepancies for artistic purpose.  I'd like to see with my eyes what it looks like to foul-up the image by "correcting" tilt by rotating the film chips.

Steve