Diffusion material for unsharp masking

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I'm about to take the plunge into Unsharp Masking. I have read that I should place diffusion material between the neg and the masking film when exposing the mask (3mm diffusion?) My question is - Should this material be clear or opaque? Many thanks to everyone for all the wonderful info on this board.

-- Yaakov Asher Sinclair (sinclair@actcom.co.il), June 07, 2002



the Radeka Masking Kit e.g. uses Kodak Duratrans as diffusion material for that purpose. Just place an unexposed sheet into the fixer. For an unsharp mask, you must either use a diffusion material or a spacer glass in order to get an unsharp mask


-- Thilo Schmid (tschmid@2pix.de), June 07, 2002.

Thanks Thilo!

I know that the Duratrans is supposed to go above the negative to diffuse any collimated light from the enlarger. Is it also supposed to go between the neg and the mask film? Also - it's no way 3mm. Are you supposed to put several sheets between the two to make up the thickness?

-- Yaakov Asher Sinclair (sinclair@actcom.co.il), June 07, 2002.


Duratrans is suitable for unsharp masks, too. The diffusion material yields the same effect as a spacer glass would. Generally, you can use any combination of diffusion materials and spacers. Two sheets of Duratrans yield a more unsharp mask than one sheet, as would a spacer glass of 4mm compared to one with 2mm thickness. The degree of unsharpness is a variable parameter and it depends on the enlargement factor and the quality of the negative/positive. There is no general rule for this. You'll have to do some experiments by yourself and learn to judge by experience.


-- Thilo Schmid (tschmid@2pix.de), June 07, 2002.

The handiest spacing material for unsharp masking is clear acetate. This can be sourced from most good art and drafting supply houses and comes in pads with interleave sheets that are very convenient and keep the film clean. You will probably find that you don't need any spacer between the neg and the mask as the thickness of the base material of the neg is usually enough to achieve the desired effect. You will probably want to use some frosted drafting film between the light source and the sandwich while making the exposure of the mask in order to keep the illumination absolutely even.

-- Robert A. Zeichner (info@razeichner.com), June 07, 2002.

i wouldn't put anything between the negative and the film. It adds another layer of things to collect dust and scratches. If you read Howard Bond's two articles on unsharp masking that appeared in Photo Techniques magazine a few years ago, you'll see that in the first article he said to use something between the negative and the film, then in the second article he changed his mind, concluded that it wasn't necessary. The only purpose of putting anything between them is to create a slight space so that the mask will be unsharp. However, Bond concluded that the space created by the back of the film and the mask (or something like that, it's been a while since I read the articles) alone was sufficient to make the mask unsharp so that nothing else was needed. Since reading his article I've stopped using anything in between the film and the mask and things have worked fine. If, however, you nevertheless wish to use something, you can go to any art supply store and buy a sheet of .003, .005, or .009 mylar and use that.

-- Brian Ellis (bellis60@earthlink.net), June 07, 2002.

I wonder how good a digitially made mask would be for alternative processes and contact printing. I'm thinking I could print masks onto transparencies (we have excellent printers at work). Or would the results be too inferior to masks made with lith film? Just curious.

-- Steve Gangi (sgangi@hotmail.com), June 08, 2002.

Why on earth would anyone wan't to make a Large format picture unsharp? Can't you just make a picture with a digital kamera and prosess it in Photoshop untill the required image occur?

-- Morten Řen (morten.oen@smartcall.no), June 11, 2002.

Ummmm why not? It's just idle curiosity, and maybe something novel to try. By the way, it is not for making the picture less sharp as the name would suggest, it is a way of fiddling selectively with the contrast.

-- Steve Gangi (sgangi@hotmail.com), June 12, 2002.

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