Questions about unsharp masks

[Steve Goldstein]

Mods - feel free to move it if you think it's better placed somewhere else.

One thing I've never seen mentioned in discussions of unsharp masking is the effect of source light divergence when making the mask. This depends on the focal length of the enlarging lens being used to make the mask, the height of the enlarger head when making the mask, and the focal length of the lens used to enlarge the masked negative.

If I want to make a mask, does it matter if I use an enlarging lens with a shorter or longer focal length when projecting light on the masking "easel"? Does enlarger head height matter? Does the anticipated degree of enlargement matter? I'm mainly using medium format (6x7) and 4x5 and almost always print 11x14 and 16x20, very rarely smaller and (so far) never larger.

Would it be better to use no lens at all and run the enlarger up high?

My 4x5 is equipped with a cold-light head. Does that make a difference?

Am I totally overthinking this?

 

[DREW WILEY]

You also have to potentially factor illumination falloff when using shorter focal length lenses. I alway use longer focal lengths relative to the film area. In most cases you want a rather small diameter pupil to the lens, to mitigate too much ray spread, which might cause more unsharp offset to the corners of the image than the center - a low risk but theoretically worth considering. If you need more halo in terms of unsharpness, it's best to do with with extra diffusion sheets between the original film and you're masking film, for sake of consistency.

Cold light head shouldn't make too much difference except with respect to controlling its exact amount of timing or exposure, which might be problematic. Do you have some kind of feedback monitoring?

 

[Steve Goldstein]

OK, so a longer focal length is better than a short one. I thought that might be the answer because of corner effects but didn’t want to prejudice my question.

I have a Zone VI intensity stabilizer.

 

[Rick A]

Greg Davis (The Naked Photographer) has a series of videos on making masks in the darkroom, one on unsharp masks.