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Hollis
26-Mar-2008, 15:14
Ok, so this came in the mail today and is quite interesting, to me atleast.

It is a projection lens, I am 99% sure of that but thats all I know. It says 'F 20" Brenkert Detroit' and has rack and pinion focusing.

The physical length of the lens is 4.5" (110/115 ish mm) and the diameter inside the barrel is 55mm. There is no stop nor does there ever appear to be a stop.

There are 2 elements cemented together in the front but are not set in the barrel but are being held in by a threaded retaining collar. In the rear there are two elements seperated by a spacer and these too are loose and being held in the same way.

This is the arrangement as I received it. I have no idea if this is the correct arrangement though.


Any and all help is appreciated.


Please refer to images...

Jim Galli
26-Mar-2008, 16:39
I would give it a bath and re-assemble like this. I have 2 similar. One is 14" and one is 18" so 20" doesn't shake me up too much. Don't know what they were for but mine are petzval but the angles at the back are so slight because of the long focal length that they are almost imperceptable. Pos - Neg --- Neg - Pos

Gene McCluney
26-Mar-2008, 16:55
Brenkert made theatrical equipment, including arc and tungsten spotlights, and pattern and star and animated effect projectors for theatrical effects, and they also made 35mm motion picture projectors and arc lamphouses for those projectors. At some point, I think in the 1930's, Brenkert was purchased by RCA and continued on into the 1950's or 1960's making theatrical film projectors as RCA Brenkert (and darned good ones). They were not specifically an optical house, and probably had their lenses made by one of the well known optical houses. I think Brenkert was the first motion picture projector to have all the gears running in a sealed oil bath. The projectors had a glass plate on the back side so you could observe the gears and the oil getting all sloshed around.

Kirk Fry
26-Mar-2008, 17:31
Hey, I got one of those on ebay several years ago, or at least the interesting retaining slots on the outside looks identical and the front has a bit of lens hood on it and no back glass. Mine says Bausch and Lomb Optical Co, Rochester NY on the side and #194916. I never did figure out what it was. I like the projector idea, maybe that slot pattern is standardized for some sort of projector or theatrical lighting equipment. The seller thought it was some sort of a telescope part but didn't really know. I just wanted to play with it. I never bought the telescope story.

K

Hollis
26-Mar-2008, 18:33
Well, cool. Thanks for the info.

Now, seeing as this is a 20" lens and I do not see myself trading my wista field camera and all 8" of bellows draw in any time soon, are any of you interested in playing with lens yourselves?

Jim Galli
26-Mar-2008, 18:54
Well, cool. Thanks for the info.

Now, seeing as this is a 20" lens and I do not see myself trading my wista field camera and all 8" of bellows draw in any time soon, are any of you interested in playing with lens yourselves?

Why not cobble it onto a piece of 3 inch waste pipe cobbled to a lens board and see what it will do for you? If you adapted it to a Nikon digital you'd find the center of that petzval as sharp as any Nikkor lens.

Hollis
26-Mar-2008, 19:32
Jim, are you trying to convert all of us over to the shit-pipe movement? I am not the optical engineer I used to be (wait, ever was). How would one go about doing this? Mainly, how do I figure out the spacing?

Jim Galli
26-Mar-2008, 19:37
Jim, are you trying to convert all of us over to the shit-pipe movement? I am not the optical engineer I used to be (wait, ever was). How would one go about doing this? Mainly, how do I figure out the spacing?

No, you'd just be using the shit pipe for bellows exension. Cut about a foot and screw it onto a lensboard somehow, mount the lens to the other end, and voila, ugliness. Like a severe top hat lens board. Then you use your bellows for focus etc. The pipe plus the bellows = the 20" focus.

Hollis
26-Mar-2008, 20:06
Ah, that makes perfect ugly sense. I will do that tomorrow and post images. Brilliant!!!