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Xowhiplock
Tinkerer
Username: Xowhiplock
Post Number: 1
Registered: 12-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, January 13, 2011 - 05:06 am: | 
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I have a Minolta MD 24mm (49) that was disassembled and determined that the focusing system was unfixable and fused together. I was wondering if I can use a 28mm MD lens and use the part in that to restore the 24mm lens to woring order?
The 24mm lens is more valuable then the 28mm by a factor of around 4 times the value, and I have a 28mm, but don't want to take it apart unless I know ahead of time that this will work.
Any help would be appreciated.
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Glenn
Tinkerer
Username: Glenn
Post Number: 889
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, January 13, 2011 - 05:18 am: |
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I seriously doubt that there will be a commonality of the major parts that are stuffed on the 24mm. However stranger things have happened, you will either have to strip the 28mm and actually experiment/compare or get hold of the relevant parts lists.
The other way is to try and separate the 'fused' parts - Try an ultrasonic bath and 'strong' degreasing solvents for congealed grease or vinegar/acetic acid in the same bath for actual corrosion induced fusing. The helical is buggered as it is, so you have nothing to loose - remove all glass before using 'acid' based products |
Xowhiplock
Tinkerer
Username: Xowhiplock
Post Number: 3
Registered: 12-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, January 16, 2011 - 11:11 am: |
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Thank you for the help Glenn. Truth is that I wrote the assembly off after determining that the lens had been glued to keep it at infinity focus, both at the ring you see off the housing and the sliding piece where the lens mounts. I wanted to see just how fused it was, so I took a torch to it, heated it up and used a pipe wrench and vice to remove it. Even at very high temp and a large pipe wrench, it was still very hard to remove, and I expected to damge the ring. Very strange that someone would use something like JB Weld to fuse these together. You can see the residue on the ring itself. I did not want a lens that could not be focused. I saved the good parts and will be on the lookout for a damaged glass 24mm to use. Keh or someplace. |
Donnie_strickland
Tinkerer
Username: Donnie_strickland
Post Number: 100
Registered: 09-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, January 16, 2011 - 06:53 pm: |
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Seems that I remember from the Cameraquest website that the US Navy used Topcon gear in the 1960s, and that they had some lenses which had been fixed at infinity in this way. Perhaps a similar situation applies to this Minolta lens of yours...maybe it was "infinity-locked" as well. |
Glenn
Tinkerer
Username: Glenn
Post Number: 891
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, January 17, 2011 - 09:10 am: |
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No idea why epoxy should have been used to limit focus on this lens - seems like iffy DIY to me!
I have come across both Nikon and Canon lenses of the Cold War period, clearly marked as US Military Property and all having their focus pegged at infinity. In all cases the lenses were in the 85mm to 100mm focal length range with maximum apertures of f1.2/f2; however, the locking of the focus was properly engineered and used a small screw. Stripping the lenses allowed the locking screw to be removed and the lenses then focused normally. Some years ago there were a number of these seen on eBay.
Contact with various aircrew, who flew out of the UK during that period, has indicated that these lenses were fitted to ordinary 35mm slr cameras and that they were used to record details on intercepted Soviet Tu-95 Bear H Bombers etc flying in International Airspace near the UK or Continental Europe.
Obviously if one has to focus a 85mm/100mm lens closer than infinity under the above stated flight conditions, then you are too bloody close and asking an itchy Soviet thumb to instigate the route to Armageddon - and people still think Cuba was the only crisis point! |
John_shriver
Tinkerer
Username: John_shriver
Post Number: 64
Registered: 12-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, January 21, 2011 - 07:54 pm: |
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The Topcon Topcor "N" lenses used by the Navy on the P-3 Orion "sub hunter" planes had an infinity lock, a latch that you could push and release. |
