Identical Cameras But Images Aligned Differently - Why?

For the past year I have been experimenting with stereo photography. I have two Canon Elph 180 cameras mounted on a flat stick side-by-side. I crop the images, put them side-by-side and email them to my phone. Then I use a vintage stereoscope viewer to view them. It's a great way to capture views that don't translate well to 2D, like snow piles.

But yesterday I noticed that there was a mismatch at the top/bottom of my photos. I thought it was my stick, but it was straight. Then I looked at past photos from two identical Lumix ZS-19 cameras (with flatter bottoms) and they had the same issue. Even placing them side-by-side on the kitchen counter, I could see a vertical difference on the screens.

I can edit the difference out of my photos in the future, but the question is: why is the vertical alignment off on identical cameras? Does the lens sag over time? These are zoom cameras so the lens extends from the camera (though I shoot at the shortest lens position to keep the views identical).

And as you can see below, the difference is significant. For being such precision devices, I did not expect this to be possible.

Snippet from upper left corner of my photos. Outline shows the difference in the vertical alignment.

Canon Elph 180. The lens doesn't protrude far when turned on.

I don't mean to sound trite, but the reason is the cameras are NOT identical.

There is a plethora of reasons why.  The prior post explains common reasons.

If you want identical, use a single camera in cha-cha mode.

I guess you are using the thread under the camera to mount the two cameras on a stick.

I have done this myself with a number of different pairs of 'identical' cameras.

The miss-alignment you have with the verticals is very common problem. It is basically because the base of the camera ( where the thread is ) is not completely flat and identical on the two cameras. One solution I use is to view the two LCDs side by side and make a note of the mismatch and then add a piece of masking tape just under the camera on one side of the place where the thread is ( so that the camera tilts very slightly forward of backwards ). Keep doing this until the images on the two LCDs are showing correct vertical alignment.

Other issues are that the zoom on each camera is not identical for the same setting. Hence one image is slightly larger than the other. This may be only 1 or 2% . It is due to normal manufacturing tolerances.

I would recommend turning off any image stabilisation as this can cause issues.

For best results put the left and right images into an app called StereoPhotoMaker which is run on a PC and this will allow adjustment so that the alignment is  virtually perfect. This software is free of charge.

In addition to Brian Flint's perfect advice, I would also suggest using two simplest heads and easily achieve alignment by adjusting them by looking at the LCD screens.