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Message |
    
Kerne
Tinkerer
Username: Kerne
Post Number: 12
Registered: 01-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, October 21, 2011 - 09:07 pm: | 
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I picked up another Mamiya TLR, C22 this time and it came with a 180mm (chrome) lens. Unfortunately this lens, despite having a super accurate shutter and nice clean glass has terrible spherical aberration across almost 2/3 of the frame (ie. blurriness around the outer diameter of the image circle). See attached photo (the center's just got a bit of motion blur from being a handheld shot).
I have a hard time believing it left the factory this way. I've already tried swapping out the top and bottom front lens cells to no avail (with all the other Mamiya TLR lenses I have the cells are essentially identical). I have tried this lens on three different bodies, so it's not the body.
Is it possible that this spherical aberration was caused by someone else fiddling with the lens groupings or removing shims somewhere?
Otherwise this lens is useful only as a "super soft" potraiture lens. 
Help!
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Tamas
Tinkerer
Username: Tamas
Post Number: 6
Registered: 10-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, October 22, 2011 - 12:15 am: |
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I could not translate very well message.
But I understand that you have problems with the lens.
I think it was opened by someone and not reassembled correctly.
Be seen if the lenses were put in position correct.
It is very difficult for someone to say what is.
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Tamas
Tinkerer
Username: Tamas
Post Number: 7
Registered: 10-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, October 22, 2011 - 12:32 am: |
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Optical diagram I found on Google.
We redesigned as to see better.
Link:
http://href.hu/x/gams
Search in the left side in the middle ( http://href.hu/x/gamt ). |
Kerne
Tinkerer
Username: Kerne
Post Number: 13
Registered: 01-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, October 22, 2011 - 08:30 am: |
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That diagram is helpful. If one of the elements did get reversed, it should be in the front cell. I'll disassemble it tonight or tomorrow and take a look.
Thanks. |
Jeffk
Tinkerer
Username: Jeffk
Post Number: 12
Registered: 10-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, October 22, 2011 - 08:55 am: |
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I'm sure it did not leave the factory that way. It's difficult to say what's going on, spherical aberration is a specific term that probably does not apply here, but most likely someone did disassemble the lens and did not put it back together again correctly. You may or may not ever find a detailed diagram of your specific lens, but there are probably only a couple ways the lens could have been assembled incorrectly, so trial and error should suffice. |
Br1078lum
Tinkerer
Username: Br1078lum
Post Number: 168
Registered: 11-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, October 23, 2011 - 07:39 pm: |
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That looks just like the effect I got when a friend of mine had me reverse the middle element in an Argus (triplet) lens for him. I would suspect the element in front of the iris on your lens.
PF |
Michael_linn
Tinkerer
Username: Michael_linn
Post Number: 35
Registered: 04-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, October 23, 2011 - 07:50 pm: |
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I would also suspect the rear element.
It should appear with a flat surface and is easy to check without disassembly. I'd start there. |
Kerne
Tinkerer
Username: Kerne
Post Number: 14
Registered: 01-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, October 23, 2011 - 09:15 pm: |
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Thanks for the suggestions. I'll find out tomorrow. |
Kerne
Tinkerer
Username: Kerne
Post Number: 15
Registered: 01-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, October 23, 2011 - 09:37 pm: |
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Couldn't wait...bingo! Turned out to be the rear-most element reversed. Also, I think that diagram is for the black version. My chrome version had a compound, bi-concave element in the rear cell as well.
You guys are the best! |
Tamas
Tinkerer
Username: Tamas
Post Number: 11
Registered: 10-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, October 23, 2011 - 10:40 pm: |
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Enjoy it!
It happens that the lens is not properly assembled. |
Dgmaley
Tinkerer
Username: Dgmaley
Post Number: 13
Registered: 01-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, October 25, 2011 - 08:31 am: |
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This was really interesting to follow. I don't have a lot of experience repairing lens assemblies and glad to see it can be done. My last experience was with a 26mm Mead telescope eyepiece given to me by a scientist that gave up on it after 20 years in a drawer. Said it would not focus properly.( it wouldn't). I found that the first lens in the stack, or rear lens had hung up slightly and was not laying flat. This left everything after it also crooked. All the glass was nicely coated and just made a really nice optic when I got done.
Dave... |
