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.

 

[Fatih Ayoglu]

I have researched this for a very long time. To my understanding there are 2 camps, with lens and without lens.
Without lens, you take the head as high as possible and then put white acrylic or white paper to diffuse the light (you keep the acrylic or paper close to the lens holder)
With lens, I make smallest f stop, lower the head to 8x10 print area, put the masking tool right in the middle. (For this you need more diffusion as the light is focused)

I sandwich the negative and masking film with a spacer in between (which is an ortho film fixed) between glass carriers. On top of the glass I have a diffusion material to diffuse the light.

For now I get consistent results and no halo effect as long as my mask is not too dense.

 

[DREW WILEY]

Not only can the degree of diffusion be controlled by various means, but the final edge effect when the mask is combined with the original for printing.

But overwhelmingly, that "first camp" option you mention, with no lens involved, makes no sense at all; and I've never personally encountered that in past literature - perhaps that's some recent DIY tweak. With no adjustable aperture in place, how can one fine tune anything? And with a lens instead, it does not necessarily mean using just the smallest f-stop.

And instead of a fixed out piece of film between the original and masking film, the almost universal practice is to have a diffusion sheet of thin translucent mylar (frosted both sides) in between. I like to use 5-mil, because still thinner 3 mil gets crinkle marks easier. And don't substitute frosted acetate. (No need for a white sheet atop the contact frame in that case, although there is nothing wrong with experimenting with one.)

Newton ring risk is a secondary issue, which can be addressed in several ways.

Practice was somewhat different when a big transparent vacuum blanket was involved, pulling things together, rather than using a registered contact frame. That was in relation to very large film sizes in the graphics trade.

Masking for color printing gets a little more involved, because one wants to be attentive of the color temp of the exposing light in relation to the specific spectral sensitivity of the masking film itself. Then if there's a color neg original (versus a chrome), one also has to null out the effect of the orange mask.

 

[Fatih Ayoglu]

Ctein's book mentions that lensless setup, and I agree, dont know how to fine tune.

To my understanding, diffusion depends also the distance between the negative and the mask as well as the material in between. Lynn Radeka suggests enough diffusion can be achieved by not using a diffusion material and Ctein shows using a glass in between the negative and masking film. Also Gregory Davis aka the naked photographer uses a fixed clear film.

@DREW WILEY can you describe your setup, I am always curios to learn a bit more on this.

 

[DREW WILEY]

Like I thought - low cost recent "alternatives", and not time-tested standard practice at all. Ctein proposed any number of hypotheticals he'd didn't personally use, or even necessarily test. He's been trying to sell off his old Condit 4X5 punch and frame, plus a lot of other stuff due to his relocation to Ireland. A piece of intermediate glass simply won't fit into one of those Condit compression frames. I hope somebody will snatch it up - matched sets are hard to find.

I have two sets of matched Condit gear, punch plus registration contact frame - an earlier 4X5/5X7 set, and a late Condit 8X10 set. In addition, I have various matched registration accessories either made or adapted by myself, including precision registration carriers for my enlargers, should I ever need those (like for dye transfer printing); but such carriers aren't needed for basic masking.

I don't know if an old Condit catalog can be found on the web. I probably have one buried somewhere; but I'm not especially interested in an archaeological career at this point in life, digging through all those old files. Condit was pretty much the gold standard for small micro-pin film registration work.

 

[Fatih Ayoglu]

@DREW WILEY you can give my name and email to him, I can buy the Condit

 

[DREW WILEY]

Just contact him at ctein.com. I don't know if he still has it or not.

 

[Fatih Ayoglu]

@DREW WILEY ok so you use Condit, you put masking film (emulsion down?) then on top Mylar (I have Duralar 0.005 matte), and on top negative (emulsion down?)
Do you put another diffusion material on top of negative?

 

[DREW WILEY]

With the masking frame and its pin glass laying on a table, with the pins facing up, the original film is punched and placed emulsion down, on the pin glass first, then the 5 mil frosted mylar sheet, and then in the dark, the masking film punched and also placed emulsion down. (Of course, this whole contact frame sandwich is inverted for exposure under the enlarger. with the glass face up.)

That way, after the mask is developed and taped to the original in register, it still retains that same configuration in the negative carrier for enlargement. The emulsion of the original will be in direct contact with the lower negative carrier glass, in correct orientation.

The only reason to use a second sheet of frosted mylar, directly between the glass and the original neg or chrome, is if there is a risk of Newton rings. AN glass was not an option yet when my 4x5 masking kit was made; but was available for my later 8x10 set.

These punch and register sets can be used for quite a number of tasks besides simple unsharp masking. For some of them, the protocol might differ from what I've just described.

 

[Fatih Ayoglu]

OK, so theoratically, there is 5 mil mylar and base of negative as a spacer in between mask and negative. Thanks a lot @DREW WILEY