[rollei_list] Re: Rolleiflex F ground glass

  • From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
  • To: <rollei_list@xxxxxxxxxxxxx>
  • Date: Thu, 1 Apr 2010 14:13:26 -0700


----- Original Message ----- From: "Elias_Roustom" <elroustom@xxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Thursday, April 01, 2010 5:59 AM
Subject: [rollei_list] Re: Rolleiflex F ground glass


What a handy reference you have there Carlso, and thank you for the effort you put into sharing it.

I've noticed on the plain grid screen that the middle is a bit warped - and aides in focusing sometimes. It makes me wonder if the liquid plastic was pumped into the mold from the center.

I also wonder if the new screens we're able to buy today from third party manufacturers are made the same way.

Probably made by injection molding. vinyl records are usually made by stamping, that is squishing out a cake of material between two heated molds in a press. RCA used injection molding for the original 45 and it was used by some others for larger records. Injection molding has some advantages for precision parts and is a common in industry. The Rolleigrid appears to be made of something like cellulose acetate, in any case its attacked by alcohol and alcohol should not be used to clean them, it will etch the surface and make them cloudy. A couple of the Rollei patents I found cover Fresnel type field lenses (what the Rolleigrid is). I will check the patents I downloaded and see if I can find the right ones.

--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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