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robcruickshank
Joined: 25 Feb 2008
Posts: 19
Location: toronto, canada
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C. Henry
Joined: 13 Dec 2005
Posts: 360
Location: North East Georgia, USA
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 Posted: Tue Nov 04, 2008 2:45 pm Post subject: |
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Rob;
I've never seen one but a wild guess is that it is a polarizer or a neutral density filter to modify one of the two images in the top range finder. It looks a bit like the filters on a mariners sextant that were used to darken the image of the sun and reduce reflections on the water when taking sun sights.
C. Henry |
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robcruickshank
Joined: 25 Feb 2008
Posts: 19
Location: toronto, canada
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| Posted: Tue Nov 04, 2008 3:51 pm Post subject: |
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| C. Henry wrote: | Rob;
I've never seen one but a wild guess is that it is a polarizer or a neutral density filter to modify one of the two images in the top range finder. It looks a bit like the filters on a mariners sextant that were used to darken the image of the sun and reduce reflections on the water when taking sun sights.
C. Henry |
Yeah, I thought maybe polarizer, since it looks a bit like some of the old polarizers that had a little viewing window on an arm, for rangefinder cameras. I couldn't figure out how it would rotate, though. |
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Les
Joined: 09 May 2001
Posts: 2682
Location: Detroit, MI
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| Posted: Thu Nov 06, 2008 2:21 am Post subject: |
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It's a focusing aid. Forerunner of the Kalart Focospot and Graflex Rangelight.
The thing on the top is effectively batteries and a light bulb, the object on the lens board is a lens. Turn the light on and when the filament in the light bulb is in focus on your subject, the subject is in focus.
The trouble with this version is it could only be calibrated for one distance so most photographers set it up for 10 feet or so and let depth of field catch any error. I have one made by Western Photo Products and they called it a Focuspot.
_________________
"In order to invent, you need a good imagination and a lot of junk" Thomas Edison |
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robcruickshank
Joined: 25 Feb 2008
Posts: 19
Location: toronto, canada
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| Posted: Thu Nov 06, 2008 2:14 pm Post subject: |
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| Les wrote: | It's a focusing aid. Forerunner of the Kalart Focospot and Graflex Rangelight.
The thing on the top is effectively batteries and a light bulb, the object on the lens board is a lens. Turn the light on and when the filament in the light bulb is in focus on your subject, the subject is in focus.
The trouble with this version is it could only be calibrated for one distance so most photographers set it up for 10 feet or so and let depth of field catch any error. I have one made by Western Photo Products and they called it a Focuspot. |
Ah! That makes sense. Thanks! A friend of mine does underwater work, and there's a similar, but more high-tech contraption on one of the underwater cameras:
http://www.flickr.com/photos/dryodora/2906709816/ |
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