Maciej Marosz I am a scientist I can see exactly what you are trying to do and test and it won't work you can't calibrate it.

Here let me save you the effort I can tell you what you are trying to see.

What you are thinking is that the light will be brighter on one side because of the motion and are trying to prove it.

The setup is terrible and you won't be able to calibrate it and worse you have air involved so you have refraction so even if you measured something you have no way of isolating what is moving the media or the light.

You have issues with lenses which have there own refractive indexes at different points each corner of a standard image has totally different characteristics ... I have discussed this with you.

You are never going to be able to make any of this work and any results you get is almost certainly going to be random chance.

Ok I can think of a fairly easy way to test your idea it would be easy to setup give me a second I will draw it.
I believe in "Evil, Bad, Ungodly fantasy science and maths", so I am undoubtedly wrong to you.