Understood, and love idea of balancing slop vs crop.
I am capturing some of the holder (from a Minolta 5400DPI film scanner) which is fine as it also includes a small gap on edge of the frame (see photo). As to the aperture of my “Any Holder Camera Film Scanner” I have a choice of 35mm or 6x7 film size, with one potentially being too tight and the other too lose (on the edges of the film strip).
I have not noticed any effects of stray light using the 6x7 aperture, but have not scanned with this holder much. Maybe I need to open up the edges of the 35mm aperture by 1.5mm as a compromise?
I had contemplated getting rid of the insert aperture altogether to simply the scanner design, making it just a base and two adjustable holder guides over a 4x5 opening, but this holder may be a reason to keep it. I will test some more.
