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Mcfly
Tinkerer
Username: Mcfly
Post Number: 1
Registered: 08-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, August 15, 2006 - 04:47 am: | 
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Hello everybody.
I bought real cheap a Porst 135mm / 2.8 lens. good optical quality, but diaphragm is full of grease. I decided to open it and clean it. my problem is that from the rear side, I got as far as I could, but the mecanism is too large to be removed from that side. It was, seemingly, enclosed from the front side.
I opened the front side but, again, I can't access it: there is one lens left between the diaphragm and me... I see no screws or any kind of opening... after long search on the net, I can't find a single manual about that lens. Can someone help me to get this diaphragm out and clean it please?
Thanks  |
Glenn Middleton
Tinkerer
Username: Glenn
Post Number: 22
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, August 15, 2006 - 08:47 am: |
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Just a guess; have you tried separating the helical, complete with the front optical cell from the barrel? If this is not the correct way, then the rear element holder of the front group must unscrew from the assembly as it is now.
Sorry that I cannot offer any specific advice on this lens. |
Mcfly
Tinkerer
Username: Mcfly
Post Number: 2
Registered: 08-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, August 15, 2006 - 12:22 pm: |
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I removed the helical, and then unscrew the front lens holder (markings ringg on the front side), removed the front lens and the one right behind it.
all that remains is the central part, with one small lens on the front side and the diaphragm mecanism just behind it. I have access to the diaphragm from the rear side but not dfrom the front one, and don't see how to remove that small lens
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Glenn Middleton
Tinkerer
Username: Glenn
Post Number: 23
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, August 15, 2006 - 08:57 pm: |
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1/ Does the bit your fingers and thumb are on, unscrew from the actual threaded part?
2/ Is that a retaining ring with no slots at the bottom of the housing - thus needing a rubber bung to unscrew? Open up iris and look in from back of lens to see if the lens is retained by a ring facing rearwards. If no sign of rear retaining ring, then lens will be retained by that ring requiring a friction tool.
3/ The alternative is that all that stuff on the rear comes off and the lens is held in by a ring from the back. I cannot make out what is exactly on the back of the above assembly, or how it is retained. Can you see any separation/part lines anywhere. |
Mcfly
Tinkerer
Username: Mcfly
Post Number: 3
Registered: 08-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, August 16, 2006 - 06:27 am: |
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1/ no possibility to unscrew it (either it is glued or really strongy screwed in)
2/ the diaphragm mecanism is supposed to be held by three small screws (removed on the photo) and is under the edge which is the same part as the body (visible on the first photo). The "yellow" ring can be removed and it frees the auto-manual selector ring, but it can't be removed either (too large to pass through the rear opening. without the three small screws that hold it in place, the mecanism can move up and down from the opening to the lens contact (maybe 5mm amplitude) and rotate freely inside the body. it seems obvious that it was introduced from the front side, before that last remaining lens which I don't know how it was fixed there.
One can see on the third pic (just below) that the front part is a separate part from the rear part of the body, but I could not unscrew it (and you can believe me, I did try), it's as if it was glued when put into place and on the inside the limit between the two parts is also visible...
in the end I start to wonder if it wouldn't be easier to just put the whole part into a solvent to dissolve the grease... |
Mcfly
Tinkerer
Username: Mcfly
Post Number: 4
Registered: 08-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, August 16, 2006 - 06:55 am: |
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on a sidenote, I found a couple of old M42 lenses in an old box in my cellar. the center of teh rear lens is scratched (they were "standing on that side) they make nice and sharp photos wide open, but when the aperture is small (f/8 and more) the scraches make a sort of a shadow in the middle of the photo. as they are not very deep, I thought of repolishing them slightly. I've read about some "toothpaste trick" but can't find the way to do it properly.
do you have a link or some indications so that I don't scratch them even more... in case they can be salvaged, ;) |
Glenn Middleton
Tinkerer
Username: Glenn
Post Number: 24
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, August 17, 2006 - 05:49 am: |
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Last pics very useful. That front bit must come off. Well it is the only way in, but on cheap optics I wonder sometimes if the designer of the mechanicals meant them to be completely stripped. I use a small vapour degreasing bath to clean bits like this. If you position the assembly in the right position, it is impossible for the optics to be touched by grease/oil contaminated solvent, as only uncontaminated vapour condenses on the lens. Thus it is usually fairly easy to insert a lens pen through the open iris for a final polish.
In your case you will have to make sure you only immerse the aperture assembly. Keep the lens uppermost at all times and use many changes of solvent. Remember Ronsonol or naphtha takes a long time to evaporate out of the assembly. Do not lay the assembly on the its side - you may find the lens covered in solvent if you do.
As for your scratched lenses. Tooth paste will not do anything on glass lenses, well it might remove the coatings. If you can lay your hands on some glass lens polishing compounds, try suppliers of DIY mirror polishing compounds that our star gazing friends use. An alternative might be Jeweller's Rouge, but this will still leave fine scratches.
No matter what you do you will remove the coating. So I would leave well alone and only use above f8 or replace, M42 optics are dirt cheap.
If the lenses were real gems, then professional polishing and re-coating would be a cost effective solution. |
Mcfly
Tinkerer
Username: Mcfly
Post Number: 5
Registered: 08-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, August 17, 2006 - 06:01 am: |
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thx for your time
gonna try all that |
