| Author |
Message |
    
Analog_in_az
Tinkerer
Username: Analog_in_az
Post Number: 3
Registered: 12-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 21, 2008 - 12:42 pm: | 
|
Hi,
I opened up a Mamiya SX 28mm M42 lens to fix a sticky aperture and ended up messing up the infinity focus (it has now become a close focus lens presently).
The problem that I can see is that I can't get the lens shortened enough to focus at infinity. I've tried to restart the thread of the focus collar onto the lens body (and align it with aperture and distance scale) but I can't get it to work. However, even with the lens a max compression (shortest length) and disregarding alignment with the aperture and distance scale, the lens does not focus at infinity. Help!
Regards
Phil |
Glenn
Tinkerer
Username: Glenn
Post Number: 383
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 22, 2008 - 02:50 pm: |
|
I can only give some general comments, as I do not know this lens. Normally the female multi-start helical is 'fastened' in a ring that is connected to the main barrel by a fine screw thread, which is actuated by the focus ring. This fine thread is usually a two or three start thread - hence problems with alignment of focus rings that are not adjustable radially with grub screws.
From your comments it appears that you have managed to get the fine threaded bits (ie the focus ring) wound too far out of the barrel, before you inserted the helical parts. Sadly this description may seem completely nonsensical to you or anybody else, who has not stripped lenses with this type of construction.
Basically you need to shorten the rear barrel, by rotating the focus ring further into the barrel, before you try and insert the male helical into the barrel/focus ring assembly.
Now; as I indicated at the start all this may all be complete rubbish, the lens in question may be of a different construction. |
Analog_in_az
Tinkerer
Username: Analog_in_az
Post Number: 5
Registered: 12-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 22, 2008 - 05:45 pm: |
|
Glenn,
It does sound like rubbish but strangely I think I understand it. I was thinking that I was not rotating the focus ring far enough into the barrel as well (using your terms). This is the only way that I can think of shortening the whole distance (essentially bringing the screw mount closer to the front element) and enabling infinity focus. |
Glenn
Tinkerer
Username: Glenn
Post Number: 384
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 23, 2008 - 09:48 am: |
|
Glad you have worked it out, now the fun starts! Just take your time and try various positions, until you get it correctly aligned.
If the lens has been repaired/serviced before, you may find some scribed lines for aligning the parts. However you may have to rotate 360 degs a few times to find the exact position - extension wise - at which the datum was scribed. You may find that using a fine marker pen, to indicate the initial position of the focus ring etc, will be helpful in showing alignments that do not work. It is very useful to know what positions you have tried - it is very easy to forget which thread 'starts' one has tried - been there done that!
Good luck. |
Analog_in_az
Tinkerer
Username: Analog_in_az
Post Number: 6
Registered: 12-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 23, 2008 - 08:43 pm: |
|
Hi Glenn,
I think I found the right combination. All combinations except one was too long to focus at infinity. The one position that would focus at infinity also focused beyond infinity. So I plan to back out the rear element to fine tune infintiy to the correct spot.
Next I need to figure out how to maintain the rear element in the correct place. I thought about a spacer but that might difficult to find the right one. So I want to use something that will glue (non-permanently) in place but allow me to unscrew it when I need to do.
As they say, you learn from your mistakes and I learned too much this time around. |
