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90mm f/6.8 Optar Film to Flange Distance

 
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VTHokiEE



Joined: 30 Jan 2017
Posts: 13
Location: FL

PostPosted: Sat Mar 18, 2017 12:29 am    Post subject: 90mm f/6.8 Optar Film to Flange Distance Reply with quote

I was wondering if anyone knew the film to flange distance for the 90mm f6.8 Optar. I've scoured the web but so far I haven't been able to find out. I was planning on using this lens for a project with the lens focus fixed at infinity.

Thanks!
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Dan Fromm



Joined: 14 May 2001
Posts: 1986
Location: New Jersey

PostPosted: Sat Mar 18, 2017 1:01 pm    Post subject: Reply with quote

As far as I know Wollensak didn't publish flange-focal distances for their wide angle lenses.

Resist the temptation to build to published flange-focal distances. Lenses as made don't conform perfectly, or even well enough, to them. You're going to have to get the lens you'll use and measure its flange-focal distance. Then build the camera.

Zeiss worked to high standards. This isn't enough. I once bought a heap of AGI F.135 aerial cameras. Each held two 38/4.5 Biogons as were sold in Hasselblad SWCs. The F.135 is fixed focus and the camera body is precisely machined. Before mounting a lens, AGI measured its focal length and FFD, marked both on the lens' barrel and made a shim, marked with its thickness and the serial number of the lens it was for, to collimate the lens to the cameras.

I ended up with 20 Biogons. Focal lengths ranged from 38.3 mm to 38.8 mm. FFDs weren't of much interest to me but they varied too.
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VTHokiEE



Joined: 30 Jan 2017
Posts: 13
Location: FL

PostPosted: Sat Mar 18, 2017 1:14 pm    Post subject: Reply with quote

Thanks for the help and advice. I'll simply measure it then, I plan on using it stopped down so hopefully that accounts for any mistakes in my measurements.
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IanG



Joined: 04 Aug 2006
Posts: 67
Location: United Kingdom

PostPosted: Fri Aug 18, 2017 7:08 pm    Post subject: Reply with quote

You don't focus at Infinity, you set focus for the Hyper Focal distance and that varies with aperture.

The equivalent 90mm f6.8 Angulong has a Flange Focal Distance of 90mm accoding to Schneider, it's gone dark early here(UK) tonight we've the remnants of the last US storm, I could see if my 90mm WA Raptar (coated Optar) is the same =they are quite similar lenses.

My experience with both the Angulon and WA Raptar is they are excellent at f22, I use my 90mm Angulon mostly hand held.

So you might want to think about setting fixed focus for say the hyper focal distance forf11, but forget Infinity focus that's very limiting.

Ian
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