Re: base-to-base mounting for Sony RX-100 #twinrig #sony3drigs


George Themelis
 

Hi Oktay, et al.,

 

That’s a good point, but it needs a clarification.

 

Consider the original image (2:3 aspect ratio) out of the RX100 oriented vertically.

 

The first step is crop. When you crop, two things happen:

  1. You lose resolution (you throw away pixels)
  2. You lose field of view

 

In the attached picture I have cropped the original image into a 4:3 landscape mode. Essentially I threw away half of the image (the bottom half). The way I cropped, I have lost field of view only vertically, not horizontally. The deviation has not changed by cropping, only the resolution and the field of view.

 

The second step is to enlarge the image to fill the display. This is a separate step but when you use SPM to crop, the image is scaled automatically so for most people this happens when you crop, but not necessarily.

 

It is in the step that the stereoscopic deviation increases. Why? Because I have enlarged the image by 2x. I prefer to think of the deviation as a function of magnification and stereo base, not so much the focal length (Deviation = Magnification x Stereo Base)

 

The stereoscopic deviation could have increased by as much as 2x, but it is possible that it is not increased that much. When I cropped the image at the bottom, most likely I have cropped the near-by objects (most likely the ground). The stereoscopic deviation depends on the distances of the near and far objects. If these have remained in the picture when I cropped, then, yes, the deviation has doubled. But if they were cropped out, then the deviation has increased less.

 

I use vertical cameras a lot. For example, my twin Sony RX10 rig. I crop and I use cropping as a way to increase the magnification. I am also using the RX0 rig vertically.  With the RX0, I crop a lot of the ground. I do not mind that the effective focal length increases, I actually like it.

 

I have not tried the RX100 vertically yet, but if you ask me what I prefer, 1) the cameras side-by-side with 112mm separation at 24mm focal length, or 2) the cameras vertically with 60mm separation and focal length of 35 to 50mm, I would say in most cases I would prefer #2.

 

George

 

 

 

 

 

From: Oktay via groups.io
Sent: Saturday, June 12, 2021 6:45 PM
To: main@photo-3d.groups.io
Subject: Re: [Photo-3d] base-to-base mounting for Sony RX-100 #sony3drigs #twinrig

 

If you use cameras in vertical orientation and crop a horizontal rectangle, keep in mind that the effective 35mm equivalent focal length will increase.
So what you gain in base will be lost due to this increase in FL if you want to maintain the same deviation.
In other words you'd need a smaller base than the one you've obtained by mounting the cameras bottom to bottom.

Oktay

 

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