[pure-silver] Re: Gelatin filters
----- Original Message ----- From: "joe mcguckin" <joe@xxxxxxx> 
To: "Pure-Silver Free" <pure-silver@xxxxxxxxxxxxx>
Sent: Monday, December 17, 2007 6:18 PM
Subject: [pure-silver] Gelatin filters
Are these made from pure gelatin or is there an acetate base? 


Joe McGuckin
Gelatin filters are made from pure gelatin which is cast into sheets. They are or were available either as plain gelatin or cemented between flats of optical glass. When in sheets they have some advantage when used in an image forming light path because they are quite thin and Gelatin has a rather low index of refraction. As a result they produce very little disturbance to the light rays. Cementing the gelatin in glass protects the rather delicate filters but the relatively thick and high index glass makes the filters less useful where they are in a vergent beam of light. Plastic filters are less delicate but the plastic has a higher index which makes it have greater effect on vergent light so gelatin filters remain the first choice where a filter must be used in light striking it at relatively sharp angles, such as on the back of a lens or for microphotophography. 

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 
=============================================================================================================
To unsubscribe from this list, go to www.freelists.org and logon to your 
account (the same e-mail address and password you set-up when you subscribed,) 
and unsubscribe from there.

Other related posts: