[pure-silver] Re: Tominon, Ysaron

  • From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
  • To: <pure-silver@xxxxxxxxxxxxx>
  • Date: Sun, 13 Mar 2005 12:01:49 -0800

----- Original Message ----- 
From: "Gene Johnson" <genej2@xxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Sunday, March 13, 2005 9:58 AM
Subject: [pure-silver] Tominon, Ysaron


> I've done some picture taking lately with a 127mm version 
> of each of these.  I'm kind of impressed.  Both of them 
> behave exactly the same as far as I can tell, in that they 
> are none too impressive wide open, but sharpen 
> dramatically when stopped down, being pretty good by f5.6 
> and by f8 are fairly amazing (folks, I spent 20 bucks each 
> for them) with serious resolution and very good contrast 
> and cover 4x5 with good sharpness all the way to the 
> corners at f8.
> I've learned that they were probably from an MP-3 copy 
> camera.  They have the standard one cell on either side of 
> the iris and are not the front mounted barrel lens type. 
> Has anyone else tried these and gotten the same results?
>
> Richard, I was cleaning the glass in a Tominon this 
> morning, and I swear the center element (Tessar type 
> construction) has a very very slight brown cast. Could 
> these things have some kind of wierd Aero-Ektar kind of 
> glass in them?
>
    The lens is probably optimised for whatever distance it 
was used at in the Polaroid camera. I think these are 
Tessars so its likely they have some coma or oblique 
spherical (look the same but come from different sources) 
which blurs the image as you move away from the center. Both 
are reduced by stopping down.
    I don't know why the center element should be brown. If 
its radio active you might be able to tell by laying the 
lens on a bit of fast film for a day to see it it fogs the 
film. Aero Ektars had one element made of a glass with both 
Lanthanum and Thorium in it. Thorium was added to some of 
the early rare earth glasses to raise their index. It was 
either not known at the time how radio active it was or else 
it was thought that the lens performance was more important 
than either stability or safety. Thorium has not been used 
in optical glass for a few decades but these lenses may be 
old enough. There are other ingredients in glass which can 
be unstable and cause staining so its not certain these are 
radioactive.
    Tominon lenses seem to be pretty common on the used 
market. I don't have one so I have no idea of how they 
actually perform.
    You can help me by seeing if you can determine the lens 
construction from reflections. I am not certain they are 
Tessars.

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

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