That is correct.Nice job. I think I see what you did, but let me make sure:
The cylinder of the shrink tubing is oriented vertically, and you punched a horizontal hole for the aperture opening. Is that correct?
Interesting idea. I'll experiment a bit and report back.The other option would be to orient the shrink tubing horizontal (so the two ends become the hole you are looking through), and you have to punch a hole on the bottom for the parture to fit in, but I think this option would be more difficult to do.