Pentacon 200mm f4

[Nelson]

Hi

I've just received a Pentacon 200f4 bought on www.leboncoin.fr

But diaphragm has a problem.

It does not open and close has it should, sometimes it does not open (or close)

it seems something is holding the blades, but nothing is blocked (i can easily press the diaph tie in the back)


Does one us you ever open a Pentacon 200 ?
Is there a chance a can fix it ?


thanks.

[Attila]

Blades are bit dirty need to clean , disassemble of this lens fairly easy. Blades cleaning also should not difficult , but need lot of patient when you assemble again. Easy to makes mistake with blades and you never able to assemble again. So do it carefully and think again always what is the next step.

[Nelson]

Nothing to loose

[Attila]

This is a good lens even if price is low , please take care of it.

[Nelson]

price low ?
I paid 30e (with postage) for it

I thinks prices have rised last years, even for those lens.

How much would you paid for that ?

[Attila]

Here this lens price around 40 EUR , I suppose under 200 EUR every price is low .These old lenses has much more value than it's price and they never go again into production. Every lens what we loose, because we don't care about them a big mistake, we revoke the possibility to get them from the next generation. In my opinion we must take care every lenses on same way than we care most expensive ones.

[Nelson]

Don't worry, i take care of my lenses

[Attila]

I would to hear this , many thanks!

[Nelson]

I dissasemble the whole lens.

Did not arrive to fix the aperture mechanism

I do not understand what is the probleme wih the blades.
Sometimes it's impossible to open or close, sometimes every thinks works well !




During my work, i made a mistake, i unscrewed the screws of the focus ring

I loose a among of time to understand it and reassemble the lense.
DAMN !

I'am not sure, but maybe i moved the "focus start".

the fact is that i can focus on infinite (i think better than with the Tair), but i'm not sure to be able to focus at 2.7m... maybe moved to 3.2m...

=> while writing my post, i tried once again to set the focus, i believe i'm now further near 2.7m...

[Orio]

Ok:
My friends photographers: if you don't know what you are doing, DO NOT open lenses. You will only obtain frustration and a trash lens.
If the lens is valuable, take it to servicing. If it is cheap, just make a gift to someone who is able to operate lenses, and buy another one.

[Attila]

Next one would be going better ... don't worry one times I tried to fix a tessar with a drop of glue and I fixed focus forever...

[Nelson]

The lense work quit well, but this crazy aperture take away the pleasure.

If i found another one in the prices i want, i'll buy

I'll keep this one.

take a look at those pictures
- the paper about 3.2m distance (after "nelson fixing")




- the CD's, about ~2.7m (after my post) with flash


click on the small picture

[Nelson]

[Attila]

[Helios]

This problem is hard to fix . You have to remove each blade of the diaphragm and then remove any "grease" dirt from them with "gasoline" for lighters (or "dry" solvents) and inspect the blades to see if they are not oxyded on their edges ! Then , you have to polish the blades with polishing media , then clean one more time with dry solvent and if your polishing give a too "blank" aspect , you have to "reblue" the steel with a gun blueing chemistry. I did the whole thing on a czj tessar's diaphragm, only for pleasure's sake ..... A near invisible oxydation of blades is sufficient to prevent the perfect "slipping" of blades on themselves. I have a K mount Soligor in this condition ...
If your lens suffers only of old dry grease on blades , cleaning would be enough. The "old dry grease" appears on elements and diaph blades after an undesired sun/heat exposition . The grease of helicoďd evaporate and condense on the nearest surface ...
The "light" fix is to remove the optical groups and rinse the whole diaph mechanism with plastic non corrosive solvent (dry fuel or gasoline is the best - known under the names of "essence C or essence F" in France. ) - Avoid the use of trichlorethylen or aceton if you're not sure the lens contains no plastic parts ...
Then you exercise the diaph mechanism until it dries.
I did so with a russian Apo-Zenitar and started the job again a few days later and unmounted completely the mechanism.
This work is sometimes perilous with some lenses...

[Attila]

Thank your for detailed explanation ! May I publish in mflenses.com maintenace section ?

[peterm1]

While on this subject can I ask if anyone knows how to disassemble the SMC Takumar 200mm f4. I have one with a sticky diaphragm. It works well enough for manual stop down but not in auto mode so I cannot use it on a Spotmatic.

The front elements of this lens are fairly easy to get off: The entire front group screws off in one unit. It is a bit hard initially due to the threads being sealed with "loctight" but once that gives way it is easy. But from the focusing ring back I do not know what to do. I had read a post that said it too unscrewed to get at the rear group and diaphragm but no matter how hard I tried it does not unscrew - even allowing for the fact that it might be sealed with "loctight." This suggests that some screws must be removed first.

Can anyone provide guidance.

[Helios]

Yes , of course , Attila ! Pentax lenses often use a black varnish to lock the rings . This varnish can be "soften" and remove with alcohool (methylic or ethylic, isopropyl also - nothing else, beware of element's coating) You have to "wet" parsimoniously the ring with cotton bud and wait a few , then try to unscrew the ring . Don't hesitate to restart this operation until it works.
Lens maintenance is frequently critical . It is often relevant of "Spitfire paradox" ... (Nobody can control a Spitfire without having already controlled a Spitfire ...) . Don't make any "lens surgery" if you cannot get the minimal documentation on it , and gather or make sometimes specific tools
I swear I didn't made any lens wreck ....

[peterqd]

[Attila]

[Nelson]

yesterday i disassembled the blades once again.
This time to clean them. In fact they were almost clean, just a few grease.

It is strange, the mechanism works very well, but when the lense is all reassembled it does not work good.

sometimes work perfectly.
othertimes does not open.

[Attila]

Perhaps some blades are little demaged or blades holder etc. who knows...

[Nelson]

I am a little bit disapointed about this lens.

It has lot of chromatic aberations.

[peterqd]

[Nelson]

Sorry

For my Pentacon (do not know if pre set is designed the same)

first :
unscrew the 3 screws on this ring


second :
move the ring to the left (before, put the focus on the minimum)
unscrew this little screw



third :
unscrew the front optical group


fourth :
carefully, unscrew the ring (i used a little screwdriver. mine came easily)



take off the screw ring, and a big ring above.

Here are the blades and the command.


ps : i believe my lens had already been opened...