Re: Un Sharp mask . no diffuser necessary

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From: Sandy King (sanking@CLEMSON.EDU)
Date: 09/25/01-09:22:02 AM Z


As I understand your explanation of the technique, you are making the
unsharp mask with items arranged in this order.

1. Exposing light

2. Sheet of white acrylic

3. Original negative or transparency with the emulsion side in
contact with the white acrylic.

4. Film being exposed, emulsion side up.

Many texts on making unsharp masks suggest placing a thin sheet of
glass or sheet of clear mylar between the original
negative/transparency and the film being exposed. You do not do this?

When using the unsharp mask in making exposures what is the
orientation of the negative and mask?

Sandy King

>Subject: Re: Un SP mask . no diffuser necessary
>
>
>
>
>On Mon, 24 Sep 2001, C Downs wrote:
>
>> .... I use a sheet of
>> white acrylic over the neg and masking film with the film emulsions in
>> opposite directions. This white acrylic being in contact with the original
>> neg's emulsion will prevent N. Rings and in my experience gives all the
>> diffusion necessary. Wess plastics makes a masking frame for 4x5 or
>smaller
>> negs that uses the same thing and I find it great for the smaller formats.
>
>
>Can you be more specific about "white acrylic"? Does it have another
>name? How thick is it???
>
>thanks,
>
>Judy
>
>The type I use is "Plexiglas" or however they spell the trademarked acrylic
>sheet that is common in the US. The more diffusion you want the thicker you
>use. The 35mm to 4x5 is a 1/16th inch thick piece and the larger negs work
>best with 1/8th in or thicker sheets. You can use thicker sheets but you
>don't seem to gain diffusion and loose light transmission. If you hold the
>white sheeting to the light and look through it you will see that some is
>"swirled" with uneven distribution of colorants while other varieties are
>very even in tone. I don't know a way to know about the types except to look
>through them. In my home area I get scrap pieces up to 20 inches for a
>couple of dollars from plastic companies that specialize in Acrylic Sheeting
>{ in the yellow pages of the phone book}
> One trick that helps to keep the sheets working if scratched or if not
>diffuse enough is to use 600 grit or finer sandpaper { auto painting type
>usually} and give both sides as even of a going over as possible.
> The same sheets are usually used for light tables and I use a piece of
>plate glass 36x96 inches {for strength and rigidity } with the thin 1/8 inch
>white sheeting over it. It is actually even enough in light transmission
>that I can use a handheld meter to read spots on different negs to see
>which will print similarly. Lot faster than warming up the densitometer...
>:o)
> Stores that sell lighting fixtures also should carry this type of
>sheeting.

-- 


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