Is a tight mask an issue?

I am not cropping in camera, and intend to use a portion of the film between exposures to set the white balance. If I use a tight mask that blocks the light outside the exposure, will the lack of direct light on the film border cause issues with setting the white balance?

Additional info; The holder I am using masks above and below the 35mm exposure perfectly, leaving the left and right edges available to use. At both ends of the 35mm film strip I get unmasked light when using the 6x7 mask under the holder. I have not (yet) seen an issue with this unmasked light, but the NLP guide warns against it, and have installed the 24mm x 35mm mask instead.

Another way of asking is: Using a modern camera/lens/hood (R5+RF100mm f/2.8 Macro), am I better off masking all potential stray light from my light source, or having the unexposed film border between frames fully lighted by my light source (for use in auto WB determination)?

A tight mask is what you want and you’d also want to shoot in a dark room. This eliminates or greatly reduces stray light, leading to more contrasty captures which will produce conversions with more distinct colours and tonality.

For white balance, you can pick it up from an almost unexposed part of an image or from an extra capture of the unexposed part of the film.

The effects of stray light depend on the qualities of your negative, e.g thin vs. dense negatives, and if you block stray light, this dependency gets less influenced by stray light. If you’re interested in knowing how your setup and negatives work in this respect, I propose that you take a series of test captures. One series could be to gradually brighten or darken the room with and without using an improvised paper or cardboard tube that shields the area between the lens and the negative from stray light.

On the other hand, I found NLP to be fairly tolerant to exposure, stray light etc. - as long as it is within certain limits. But you’ll never know these limits until you try to push them.

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Thanks. Having just scanned a few thousand mounted slides I am a bit spoiled with the integrated mask.

With a tight mask in the form of a 24x36 aperture 3/32" below the film plane what should I watch out for in terms of issues?

I assume alignment will be critical otherwise one edge will darkened. Could the distance to the film plane cause vignetting, or worse darken all four edges of the film?

Well, the mask being farther away than the slide, the mask will look smaller than the slide, unless the slide frame is cut to 23x25. For mounted slides, I’d use a mask in slide frame outer dimensions, specially if you capture the slides at very close to 1:1. Don’t overdo “tight”.

The goal of the mask is to prevent a contre-jour situation that can reduce imaging contrast.

Again, don’t over-tighten your masks. It’s only complicating your workflow. If you allow the capture to include some of the frame, you can always correct slight misalignment in post at the expense of a few wasted pixels. Balance slop and crop vs. the time you have to spend positioning the slides.

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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.