> Richard Schätzl wrote:
> >Ups... (sound of breaking glas) The 85mm/2.0 lost, with the time, one
>>lens element.
> You are correct, Richard. The second and third elements which were
>glued to form one element, were replaced in the multicoated version by a
>single element the same size and shape as the glued combo. I presume the
>manufacturing technology improved. The 85mm also gained two millimeters
>in physical length. Must have been the thickness of the multicoating. :-)
> Regards, John Austin Oakland, CA
With higher-index glasses, the need for a great number of elements decreased.
These cemented pairs or trios -- sometimes even quads -- of lens elements
in old
designs had glasses of different refractory indices in order to master
aberrations.
The cementing held down the number of free glass-air surfaces, which even with
single coating reflected enough light to be troublesome. (Without any
coating at all,
as in the old Zeiss super lenses, each of them reflected ca 4 0f the
light! So the
designers tried to keep the air-glass surfaces down to maximum six, as in the
Tessar and Sonnar designs. They performed prodigies of ray-trace computation
(without computers, remember) and miracles of lens grinding and cementing!
Vänliga hälsningar/Best regards
Lars Bergquist
Välkommen till/Welcome to ...
<http://www.bahnhof.se/~timberwolf/>
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