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Contax_crisis
Tinkerer
Username: Contax_crisis
Post Number: 4
Registered: 08-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, August 19, 2008 - 05:01 pm: | 
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This Lancaster Rectigraph has pretty badly contorted aperture blades which limit its maximum aperture to f16 (approx).
It's a traditional British barrel lens and I've no idea how to open it; the mounting is done with all the fixtures hidden from the exterior. The front element unscrews, and a long pin can tap against the metal aperture blades which are warped. It seems that the only way to straighten them out would be to take them out of the barrel and hammer them flat again.
Has anyone any experience in repairing aperture blades like this? I've never opened up a vintage barrel lens like this, and the last thing I'd want to do is turn it into a lens which needs a slot cut for the use of waterhouse stops. |
Glenn
Tinkerer
Username: Glenn
Post Number: 403
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, August 19, 2008 - 06:03 pm: |
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Do not let any hammer near the blades, you will ruin them. Hammering will work harden the metal, thus you will never get them flat without heat treatment also. To flatten the individual blades, you need to gently rework the blade between two pieces of hard wood - I use two pieces of Boxwood. You will find that you need to 'over straighten' some blades, in order that they stay flat. To facilitate this, one of my boxwood blocks has a number of various radius curves machined into three of its faces.
As to opening up the lens:- On my three unnamed examples, everything is held internally by RMS threaded rings. None of the rings have any slots cut in them to aid removal,but were easily unscrewed using rubber 'O' rings superglued to lengths of plastic pipe.
Sorry I cannot offer any more specific help in this matter, as I fully understand your reluctance to modify to Waterhouse stops. |
Contax_crisis
Tinkerer
Username: Contax_crisis
Post Number: 9
Registered: 08-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, August 21, 2008 - 04:51 pm: |
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Thanks for warning me Glenn (before I end up destroying the blades).
I'll start looking into the lens to see if I can unscrew it this way.
Many thanks. |
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