Unusual Optical Fixture?

Scheimpflug · Expire: 2011-11-18

Does anyone have any thoughts as to the original purpose of this fixture?

It has one huge lens element and one small lens element, both on a long set of sliding tracks. There is a geared knob which will move the small lens over a very small range, and the small and large lenses are linked together such that they both move together (but at different rates). The whole assembly is very heavy (16 lbs / 7.25 kg) and extremely sturdy. At the end, there is a universal iris diaphragm, a metal plate with a medium-sized circular hole, and then a pair of two moveable bars which open/close on parallel tracks behind it. Everything is lever operated, spring loaded, etc, and built like it would be used frequently.

Any thoughts on what this fixture might have been used for? Question

Himself · Expire: 2013-05-30

I'm curious too.

Scheimpflug · Expire: 2011-11-18

I've made a thread over at APUG to get this in front of a few more eyes. We'll see if anyone over there recognizes its purpose. Wink

http://www.apug.org/forums/forum147/97341-unusual-optical-fixture.html

Spotmatic · Joined: 18 Aug 2008 Posts: 4045 Location: Netherlands

Well, I put my Googling skills to good use (I hope). But I'm almost 100% sure that this was part of an optical bench, which was used to experiment with optics. Just do a Google image search on "optical bench" and you'll see that I'm right Smile

kds315* · Expire: 2021-03-09

The iris looks rather burnt, so I would guess it was once part of some special illumination system (two condensor lenses, one big, one small) and behind is an adjustable slit, so maybe that was for some optical experiments (school, university) on optics?

Scheimpflug · Expire: 2011-11-18

Mystery solved on the APUG thread. It's from a carbon arc theater spotlight. Cool

Klaus, you were very close!

I've done a bunch of searching based on this, and I'm thinking this assembly may be from a "Strong" brand carbon arc spotlight:

(image from: http://blog.huntingtontheatre.org/2008/09/strong-carbon-arc-spotlight.html)

It has the same red knobs, in the same locations, and with the same knurled adjustment knob as well. Cool

David · Expire: 2013-01-25

Time to see if it can direct light the other way, too. Tape a camera behind that aperture and see what you get!

Scheimpflug · Expire: 2011-11-18

David · Expire: 2013-01-25

I remember that thread. So when you put a lens in the diaphragm and tighten it, does it clamp well enough to allow lens focusing? Will the iris wear our over time from clamping down on lens mounts?

Scheimpflug · Expire: 2011-11-18

I think generally people use them with non-focusing lenses (enlarger, medium/large format, etc), and then focus them with bellows... But the iris seems reasonably durable. I wouldn't mount anything *too* heavy in it, but it seems fine otherwise. It's really just a catch-all device for the unusual lenses... not something to use every day. Time will tell how well it holds up. Cool

Scheimpflug · Expire: 2011-11-18

A bit more info:

The small lens is biconvex, and measures about 2 inches / 50mm in diameter.
The huge lens is plano-convex, and measures about 7 inches / 175mm in diameter.

I don't have any infinitely long rooms in my house, so I can't measure the infinity focus just yet. Very Happy

But focusing on a light source about 14 feet / 4.25 meters away, the small lens focuses at around 60mm, and the huge lens focuses at around 15 inches / 380mm.

Together in the fixture, the assembly focuses pretty much right at the aperture. The aperture is on a fixed (welded) bracket, so mounting a camera will be difficult. Neutral

Holding a sheet of paper over the aperture though, I can focus an image pretty easily. The zoom range is quite large, but the combined focal length actually isn't that long, even at the far end. Certainly less than the 300mm lens I have handy to compare it to. I will have to make some more precise measurements to figure it out for sure.