[pure-silver] Re: Tominon, Ysaron

----- Original Message ----- 
From: "Gene Johnson" <genej2@xxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Monday, March 14, 2005 3:33 PM
Subject: [pure-silver] Re: Tominon, Ysaron


> BTW, with regard to these lenses,  Doesn't anyone but me 
> think it's
> interesting that they should make them exactly 127mm f4.7?
>
>
    I think this is a limitation of the shutter maximum 
aperture. For instance, Kodak made two versions of the Ektar 
used on the Medalist camera. The Medalist lens was 100mm, 
f/3.5, the stand alone version for 3x4 press cameras was 
105mm, f/3.7. The ratio of the focal lengths and stops is 
exactly the same. Someone once said that Rudolf Kingslake 
said in a lecture that both lenses used exactly the same 
elements but spaced to change the focal length. I think that 
can't be quite true because such a change would probably 
throw off all the corrections. But, you never know and I 
don't have the prescriptions for either lens.
    The 127mm, f/4.7 Ektar as used on press cameras, is 
limited by the maximum clear aperture of the No.2 Kodak 
Supermatic shutter. The next larger size shutter is much 
larger and operates only to 1/200th second rather than to 
1/400th.
    127mm is exactly 5 inches and is the right diagonal for 
3-3/4 x 4-3/4. The Kodak Ektar is remarkable in being able 
to cover 4x5 with corner to corner sharpness at f/8. This 
lens was used on 4x5 press cameras because press 
photographers wanted a slightly wide angle lens. The 135mm 
Tessar, which was standard on 4x5 Speed Graphics is also 
somewhat wide angle for the format. Normal is 152mm.

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

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