Re: Kohler illumination question...


"Klaus Henkel" <KlausHenkel@xxxxxx> wrote in message
news:3dj4ngF6p4qflU1@xxxxxxxxxxxxxxxxx
> Aaron schrieb/wrote:
>
>> The frosted element in my illuminator is 1/4" in front of the halogen
>> bulb. The light passing through the frosted element is focused
>> thereafter. Would you explain why the light coming from the filament
>> is different from the light coming from the frosted element just prior
>> to the focusing?
>>
>> I think there is some confusion about the role of the diffusing
>> element since some designs place it at the plane of the field
>> diaphragm/field stop just prior to the light entering the condenser
>> while others place it immediately infront of the lamp filament prior
>> to the light being focused. In this discussion we have not
>> differentiated between these two approaches. Would you comment,
>> please?
>
> Hello Aaron!
>
> reading your qestions to Andy Resnick and earlier contributions in
> this thread, it seems to me, the term "frosted" does not take into
> account properly, that the first lens-surface of some Zeiss
> lamp-collectors ist not ground. Its mat surface is achieved by
> hydrofluoric acid, which leaves thousands of little bowl-like concave
> hollows in the lens-surface. They are of different diameters, but all
> of the same focus-width - tiny concave lenses on the surface of a
> concave lens.
>
> The result is, that light-rays are not being scattered in all
> directions, as would be the result of a simple ground glass, but the
> light beams entering the first collector lens, are just "widened" and
> defocussed, changing the image of the lamp filament into a homogeneous
> image, mixed together out of thousands of little lenses. This design
> does not fully destroy the definition of the field diaphragm.
>
> Frosted in that special way the lighting force is reduced about
> 20-40%; that is not much, compared with reduction of 60-80% through a
> normal ground glass.
>
> There were, to my understanding, some rather different reasons, which
> lead the design team at the plant of Carl Zeiss (Winkel) in Goettingen
> 1949 to this interesting and well working solution for a
> Koehler-illumination.
>
> Transatlantic greetings from Bavaria!
> Klaus Henkel

A friend of mine worked at Kodak way back when. He made a standing offer, I
come to Rochester and he would show me the "black" portion of the Kodak
Museum. Unfortuantely this wasn't things like what members of the Kodak
family had tails this was the stuff that they didn't show. Only fanatics
like me would enjoy it.

One of the neat parts was Kohler type light bulbs. One requirement for this
was the filament had to be flat, not circular. Making these was difficult.
The way around this was to use a "ground glass" and more conventional lamps,
a lot of times Zeiss after WWII would use Mercedes light bulbs. Not that
they were Mercedes but both groups wanted a well designed lamp.

Kevin Cunningham
SMS


.

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