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DIY apertures for salvaged Dogmar

 
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ratchet909



Joined: 12 Feb 2021
Posts: 2
Location: Indiana

PostPosted: Fri Feb 26, 2021 4:41 pm    Post subject: DIY apertures for salvaged Dogmar Reply with quote

Hello all,

This is my first post and I'm new to Graphics. I have a Miniature Speed with a what appears to be a decent Optar in a nicely-working Graphex shutter, but I also obtained a Goerz Dogmar 5"/4.5 in a non-functioning (frozen up with rusty blades) Compur.

I'm working through my first roll of film to test everything, but as I had some free time and scrap acetal plastic I removed the Dogmar elements, machined a one-piece lens board (threaded to receive them at the same spacing as the shutter), and then realized that I have no way of controlling aperture. It's just wide open all the time. I did take a shot with it using the FP shutter, which likely needs tuned up but works and cycles through apparently okay (but that's a post for another day).

My question is: Can I simply machine some lens caps with varying size openings to function as an aperture control? Would it be best to do this with the front or rear element? Or must the aperture be installed between the elements as it was in the shutter?

Thanks much!
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45PSS



Joined: 28 Sep 2001
Posts: 3981
Location: Mid Peninsula, Ca.

PostPosted: Fri Feb 26, 2021 7:34 pm    Post subject: Reply with quote

I think the aperture needs to be in the center between the two cells. I have never seen one that wasn't.

The formula for f numbers is focal length/entrance pupil. The entrance pupil is the diameter of the aperture opening as viewed through the front lens element (cell).

Waterhouse stops https://en.wikipedia.org/wiki/Waterhouse_stop will be the way to go.
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ratchet909



Joined: 12 Feb 2021
Posts: 2
Location: Indiana

PostPosted: Fri Feb 26, 2021 8:49 pm    Post subject: Reply with quote

Thank you! I feared as much. I'll have to do a little thinking and measuring and drawing to pull that off, but it seems doable. Nothing to lose...it'll be a good exercise anyway. I'll post more pictures of the thing if I can make it happen. As it stands:

Dogmar Project by Robert, on Flickr
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Dan Fromm



Joined: 14 May 2001
Posts: 2079
Location: New Jersey

PostPosted: Sat Feb 27, 2021 2:08 pm    Post subject: Reply with quote

Check the threading. The 5"/4.5 Dogmar might, just might, fit a Compur/Copal/Prontor Press #1.
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45PSS



Joined: 28 Sep 2001
Posts: 3981
Location: Mid Peninsula, Ca.

PostPosted: Sat Feb 27, 2021 9:56 pm    Post subject: Reply with quote

pm sent.
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