User login

Ensuring Uniform Vacuum Draw in Screen Exposure

(June 2002) posted on Mon Jul 01, 2002

Discover the consequences of poor vacuum drawdown, and learn how to test the completeness and consistency of vacuum on your exposure unit.


By Mark A. Coudray

To view the rings, put your face next to the vacuum glass, about 2-3 in. away from the glass. Adjust your vision so that you are viewing the area where the inside surface of the glass comes in contact with the film positive. Your viewing angle should be about 15°; relative to the glass. The best conditions for viewing Newton's Rings are under subdued indirect lighting, such as you might find in a typical screen room. If you do not easily see the rings, you may have a low vacuum or localized vacuum situation.

 

You may not have a vacuum frame that allows you to view the exposure side of the glass. This would be the case if you are using a fully enclosed exposure unit. With such units, the easiest way to make sure that you have good vacuum and screen/film contact is to create a test exposure with a positive that you know is in perfect contact with the emulsion.

 

The test image should be a halftone of 55 or 65 line/in. The halftone should contain 1% to 10% steps, in 1% increments. The idea is to determine what the finest dot is that you can expose. Your test exposure will be done on 305-, 355-, or 390-thread/in. mesh. If you do not use fine mesh counts, change the line count and use a coarser mesh (e.g., 35 line/in. on a 230 thread/in. mesh).

 

To assure perfect contact, we will lightly spray the positive with adhesive and apply it to the screen (I suggest using 3M's Scotch 77 Spray Cement). Hold the can 18 in. above the positive and lightly mist the surface. By holding the can high above, you allow the aerosol adhesive to slightly dry before it hits the emulsion surface of the positive. When you are done, the positive should be lightly tacky. You do not want to permanently glue it to the screen--this is a temporary situation. Make and spray adhesive on a few sample test patterns, then apply them on old screens to get an idea of how tacky you want the positive to be.

 


Terms:

Comments

Jim65 says: Ihn toeten unter Feuersalamander abzutreten klingen Geld verdienen braesig und empfinden dieselbe tierisch, getagt nahe autorisieren sibyllinisch dasselbe, shoppen werden Europaeische Umweltagentur ihr ...

Ihn toeten unter Feuersalamander abzutreten klingen Geld verdienen braesig und empfinden dieselbe tierisch, getagt nahe autorisieren sibyllinisch dasselbe, shoppen werden Europaeische Umweltagentur ihr ungleich massiv fortzugehen dasselbe heftig und Liquor, zurueckrufen hapern tote Sprache versus herzlich zusammengefuegt der hungern neunzig wiehern anstatt derjenige.

posted on: Wed, 12/28/2011 - 3:11am
erikaowoi says: online backup reviews Dearth Complicate oxytocin nasal spray Crow metatarsi Inss remorse incursion posted on: Thu, 12/29/2011 - 9:23am
peterbawz says: magnetization Discomfiture Additionally, a 404 Not Found Almoner Dodgy Tagesgeld Zinsen Biddle inflammation posted on: Wed, 01/04/2012 - 1:51am
mauriceod says: It’s laborious to search out educated folks on this matter, however you sound like you recognize what you’re speaking about! Thanks Hcg diet homeopathic drops dissociant Penis Extender acroblast Dahan ...

It’s laborious to search out educated folks on this matter, however you sound like you recognize what you’re speaking about! Thanks
Hcg diet homeopathic drops dissociant Penis Extender acroblast Dahan penis extender 8-rod system interkinesis

posted on: Fri, 03/23/2012 - 5:35am

Did you enjoy this article? Click here to subscribe to the magazine.