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Subject: Pentekarem prism

From: Bill Cook  <billcook50@___l.com>

Hello Brethren:

I need a prism (a good prism) for a Zeiss Jena 15 x 50 Pentekarem, and some of the people listed by Zeiss as doing Jena work--and having parts--actually have their work done here. Thus, I am looking for a source NOT on their list.

Please help.

Kindest Regards,

Bill

PS Does anyone know where Hardie, from ZV Service went? Did he retire? Pass away? Go to work for Jason? etc.?

===============================================================

Subject: Zeiss prisms

From: "Steve Stayton" <sstayton@___ink.net>

>I wonder if any member of the list knows what type of Schott glass was used

>in the prisms of the first Zeiss binoculars ?

Early Zeiss porro prisms:

A 1902 publication, Jena Glass and Its Scientific and Industrial Applications, by Dr. H. Hovestadt catalogs the then standard "Jena Glasses" (later to be known as Schott glass). The most likely candidate glass used by Zeiss for porro prisms used in binoculars is Jena catalog number O.144 Boro-Silicate Crown. The listed catalog glass properties for O.144 are:

ND (589.3nm) = 1.5100

Abbe v number = 64.0 (based on ND, F, C at 589.3, 486.2, and 656.3

wavelengths)

Density = 2.47

Exceptionally hard, very colourless.

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This glass is running number 5 in the catalog list of the first 44 Jena glasses that date to a 1886 catalog listing according to Hovestadt.

This early Jena glass type O.144 would appear to be very similar in properties to the later Schott glass type BK1.

Measurements that I made a few years ago on a ca.1900 Zeiss Feldstecher porro prism (kindly supplied by Jack Kelly, thanks Jack) and a Bausch & Lomb Zeiss Stereo Field Glass porro prism from the same era were as follows:

Zeiss:

ND = 1.5110

Abbe v number = 66.4

Specific gravity = 2.47

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Bausch & Lomb Zeiss:

ND = 1.5109

Abbe v number = 66.6

Specific gravity = 2.47

*************************

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