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Correct rangefinder cam for 180mm Rodenstock Sironar-N 5.6

 
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MonkeyBrain



Joined: 05 Nov 2011
Posts: 49

PostPosted: Wed Apr 24, 2013 2:32 pm    Post subject: Correct rangefinder cam for 180mm Rodenstock Sironar-N 5.6 Reply with quote

Hi all,

Aside from the obvious nightmare of trying to find the correct top RF cam available to purchase somewhere (and I'd rather pull my toenails out one by one that try to make one, so don't suggest it, thanks), I have another problem in that I'm not even totally sure which cam this lens requires. And this chart doesn't help too much either:

http://www.graflex.org/speed-graphic/top-rangefinder-cams.html

See what I mean?

Presumably I should be trying to track down the p-62 cam, for a 180.5mm lens (.5? why?) and not the p-74, for a 179mm (does such a lens exist?).

I've no idea how these things work, and therefore can't conceive as to why a cam would exist for either an 180.5 or 179 mm lens and not for the 180mm, but I do have sufficient faith in Graflex that that there will be a perfectly good reason for this, and that no doubt in practice, and depending on some obscure variables, my 180 lens is actually closer to one of the above measurements than 180mm.

Can anyone tell me which cam I need (if you're feeling really patient and charitable, perhaps even why)?

And if luck is really shining on me, sure would be great if someone actually had one of these cams to spare!



Ok, perhaps that last bit is a little over optimistic. One step at a time...
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45PSS



Joined: 28 Sep 2001
Posts: 3218
Location: Mid Peninsula, Ca.

PostPosted: Wed Apr 24, 2013 6:47 pm    Post subject: Reply with quote

The printed focal length on the lens is the nominal value. Due to production tolerances lens will be the nominal value to a few millimeters either side of the nominal value. To know which cam you need you need to have your lens optically measured for its focal length.
Cams 88, 74, 62, 41, and 76 are potential matches.
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MonkeyBrain



Joined: 05 Nov 2011
Posts: 49

PostPosted: Wed Apr 24, 2013 6:57 pm    Post subject: Reply with quote

Hi, you well? Been a while.

Obviously that's totally NOT what I wanted to hear, but thanks for breaking the news to me anyway.

So, how does one go about optically measuring a lens?

Man, these Graflex's are complicated to get them how you want them. Suddenly the price of a Linhof Technika doesn't seem all that over the top after all.
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45PSS



Joined: 28 Sep 2001
Posts: 3218
Location: Mid Peninsula, Ca.

PostPosted: Thu Apr 25, 2013 2:35 am    Post subject: Reply with quote

Quote:
So, how does one go about optically measuring a lens?

Use a collimator being you can no longer send it to the nearest Graflex Service Center for collimation.
http://www.kyphoto.com/classics/collimator.html

Workaround: mount the lens on the camera; mount the camera on a tripod and level the camera on all axis; focus the lens on an infinity target at least 1.524 kilometers away, closer will give a false reading; lock the rails.
Measure from the center of the lens, usually the aperture blades but not always, to the film plane/front surface of the ground glass. Some lens are designed to have shorter than their focal length back focus, check the manufacturers specifications to find if this is true for your lens.

Quote:
Suddenly the price of a Linhof Technika doesn't seem all that over the top after all.

The parts such as cams are expensive they are custom cut for each lens.

A cam that is mismatched will cause a focusing error at the close focus distances increasing the error as the divergence from the desired focal length increases.
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MonkeyBrain



Joined: 05 Nov 2011
Posts: 49

PostPosted: Thu Apr 25, 2013 7:58 am    Post subject: Reply with quote

Thanks for the info, sounds like a lot of fun...
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vickko



Joined: 02 Mar 2013
Posts: 6
Location: Canada

PostPosted: Fri Sep 20, 2013 1:16 pm    Post subject: cams, sigh Reply with quote

aaarggghhh

I have a similar challenge, with a 150mm and 110mm lens.

Looks like I'll be making cams.

Can't be that hard, can it?
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Vick
35mm: Leica, Nikon
120mm: Hasselblad, Rollei, Fuji, Voigtlander, Zeiss
4x5: Linhof, Crown Graphic
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