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Setting Focus on Model 22

 
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jdman



Joined: 13 May 2001
Posts: 302
Location: Midwest

PostPosted: Sat Jun 08, 2002 1:23 pm    Post subject: Reply with quote

Has anyone ever adjusted the focus on a model 22? Would you measure to the film plane? Thanks, Russ
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Jim23



Joined: 08 Sep 2001
Posts: 126
Location: US/Greater Cincinnati, Ohio

PostPosted: Wed Mar 05, 2003 8:02 pm    Post subject: Reply with quote

I placed a ground glass (actually a discarded Yashica focusing screen) on the film plane, and using a loupe, focused on a distant (appx. 2km) antenna tower (to approximate infinity). The focusing screen at the film plane indicates perfect focus as well as the ground glass on top. Thus, they match as well as the focusing knob is indicating infinity; however, there is a strange problem. At intermediate distances (for example 10 feet focusing on newsprint) the ground glass at the film plane and the finder still match nearly perfect focus. The problem is that the distance scale on the focusing knob lies (by about 2 feet!). Thus the lenses have very close match on their focal lengths, but they don't match what the scale on the knob says except at infinity. My guess is that the taking lens is not the advertised focal length, and it was matched with an equally-off viewing lens, so therefore the focusing scale is not correct. Is this possible?
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Baker



Joined: 08 Apr 2002
Posts: 85
Location: Texas

PostPosted: Wed Jan 14, 2004 3:35 am    Post subject: Reply with quote

Quote:

On 2003-03-05 12:02, Jim23 wrote:
My guess is that the taking lens is not the advertised focal length, and it was matched with an equally-off viewing lens, so therefore the focusing scale is not correct. Is this possible?


Sounds reaonable -- the Graphic press cameras had several different scales for each nominal lens focal length, which were matched up after testing the lens to find its exact focal length; with a non-interchangeable scale, it's entirely possible for it to be a little off due to the tolerances of the lensmaking process.

I certainly hope they'd go to the trouble of matching the two lenses to each other, though.

[ This Message was edited by: Baker on 2004-01-13 19:35 ]
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glennfromwy



Joined: 29 Nov 2001
Posts: 903
Location: S.W. Wyoming

PostPosted: Wed Jan 14, 2004 4:44 am    Post subject: Reply with quote

I have tested the focus on a great many old TLRs and others using the same method. My experience is that almost none of the focus scales correspond with ground glass focusing. It's not really a big deal as the lenses were made to be stopped down and depth of field will carry it. Hopefully, if using scale focus, you would be focused just ahead of the subject for this to work well.

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Glenn

"Wyoming - Where everybody is somebody else's weirdo"
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