[LargeFormat] Elgeet Update

[Richard Knoppow]

----- Original Message -----
From: "Les Newcomer" <lnphoto@twmi.rr.com>
To: <largeformat@f32.net>
Sent: Tuesday, March 04, 2003 3:18 AM
Subject: Re: [LargeFormat] Elgeet Update



On Tuesday, March 4, 2003, at 02:31 AM, Clive Warren wrote:

> Alan,
>
> Richard may have mentioned this earlier, but in1962 the
Elgeet 'firm
> acquired ownership of the ancient establishment of
Steinheil in Munich'
> (from Kingslake).

> The only mention of large format lenses I can find is the
Elgeet
> Anastigmat f4.5 250mm which is of course your lens. Be
wary that the
> circle of illumination is probably larger than the useful
image circle.
>
> Cheers,
>            Clive
>
>

Looking up Steinheil in  my '39 ed of "Handbook of
Photography"  I find
they made a 250mm f4.5 Unofocal lens.  This was similar to
the Celor and
Aviar, and later the Artar.  It has 4 symetrical air spaced
elements  with
an angle of view of 60°, and is the basis of most process
lenses.

If we let a= the radius of the coverage angle, then 2a=
2[focal length x
Tan (half the angle of view)]  will give us the circle of
coverage.  Thus

2a=2(10 x Tan 30°)

2a= 2 x 5.7735"

2a=11.54"


  You can get some idea about the construction of a lens by
counting the reflections from the surfaces. Glass-air
surfaces, even when coated, will be bright, cemented
surfaces will be dim. Use a small source, like a pencil
flashlight, to get clear reflections.
  I am skeptical that any Steinheil lenses were made
carrying the Elgeet trademark. The Unofokal was a well
respected design. A dialyte type but with all elements
having the same power (thus the name). It would be
interesting to know what this lens actually is, the
reflection trick will show whether it is a dialyte or a
Tessar, or something else.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com