Auto pentacon MC 1.8/50 M42 version stuck aperture blades?

[mo]

I have received this lens and it is stuck wide open The A/M switch works as the pin can be depressed.The Aperture turns and you can feel the faint clicks as it turns but no blades appear.I found this discussion about what seems to be my problem with this lens
Flickr discussion
I can do the first part what is suggested and remove the front part of the lens but how do you remove the helicoil is it I have to unscrew the 3 screws and then lift it out to get at the Aperture blades?Thanks for any help.
My lens
#1

#2

#3

#4 removing the front with my adapted sink plug..

#5 Do I unscrew these 3 screws?

[peterqd]

Hi Mo, the three screws are used to clamp the outer part of the helicoil to the focus control. When you turn the focus the outer part of the helicoil turns and the inner part remains still, held with the "prongs" which you'll see if you remove the mount end. These screws need to be released to calibrate infinity focus.

I think I remember that it's not necessary to dismantle the helicoil to clean the blades on this lens. If you can avoid this and leave these three screws alone, it won't be necessary to recalibrate the infinity focus again.

I have a copy of this exact model lens in a dismantled state, but it's packed away up in the loft and I'll need a little time to dig it out. I'll get back to you in a while.

[mo]

Thanks Peter,after a few failures in putting lenses back together I would appreciate not having to pull apart the lens...

[Kathmandu]

Hi Mo,

Until Peter digs up his pictures. I have some from a while back where I had to lubricate the aperture. I did it without opening too much and got my aperture to work.



Heres the link:

Mines not the MC version and I am curious if they are built alike-they should be.

Cheers

[mo]

Thanks I will keep your link in mind....Very handy indeed.

[peterqd]

OK, here we are, sorry about the delay. In fact my lens is the electric version, but otherwise it's identical to yours Mo.

You can get to the aperture blades quite easily from the rear mount end, but if you need to remove them you'll need to go in from the front end. Usually it's possible to clean the blades with lighter fuel without removing them, just soak them and keep working them until they're properly dry.

First, remove the three screws holding the mount onto the body. The mount will lift off and probably the A/M slider will fall off as you do it. This is NOT a problem! However, don't remove the aperture dial if you can avoid it, as there's a little bll bearing on a spring inside which will jump out and hide itself permanently on the other side of the room.



Now you'll need a tiny 1mm screwdriver to loosen the three grubscrews round the outside of the rear element as in this pic. Loosen them to about what I've shown here and then screw back in half a turn before removing the screwdriver - this prevents the screws from falling out.


The rear element can now be lifted out and the aperture blades are just underneath.


When you've cleaned the blades, replace the rear element and tighten the grubscrews. Place the A/M switch slider on the rim of the mount part as shown in the pic, and then carefully replace the mount on the body, making sure you connect the "fork" with the vertical rod that actuates the blades. Make sure the blades are wide open when you do this and that the aperture dial is at the 1.8 stop. This lines up the screw holes and you can replace the three screws and tighten up.


It would be sensible to clean the auto aperture mechanism in the mount with the same fluid before you reassemble it.

Good luck!

[mo]

Thanks Peter I have some spare time tonight and will give it a whirl. do you have to use lighter fluid as strange as it may seem it is hard to come by where I live..

[peterqd]

[BRunner]

Here is my photo-guide, cleaning aperture on Pentacon MC 1.8/50.

[Gonzoo]

Mo, visit your local chemistry and ask for bezine (german term is "Waschbenzin"). It should be available easily. Works as good as lighter fuel. Take care to use it with good ventilation and no fire nearby

[mo]

Well I have the back off and the blades are there...very stiff to get the blades moving but not a lot of grease visible on the blades at all.The lens has been opened before as there are a ton of markings.
I will reassemble and see if maybe they did not line the fork up properly last time it was opened.
I do see the little ball bearing and happily it did not go to the other side of the room....I also removed the cat as she wanted to help...

[mo]

Thank you Gonzoo,I will have to look for it.
I have disassembled the back of the lens twice and no luck getting the blades to work.When I have the back off exposing the aperture lever, you can move the lever easily with your hand and the blades move ok...It is just that initial movement "grips" then the blades move freely. Would that "gripping" at the start be enough to stop the blades moving using the usual action of the aperture/f stop ring?
Or could there be something else wrong? I will try to obtain some BENZINE and see how it goes after that.

I don't want to open the lens up any more than that...unless I really have too.

[BRunner]

You must disassemble entire aperture mechanism and clean all blades separately. See my link few posts above.

[mo]

[Gonzoo]

If the gripping is caused by oil stuck blades, you will be successful with benzine. Be patient and repeat cleaning procedure a number of times. It may take some time to dissolve old grease/oil. Otherwise it is something mechanical, e.g. weak spring or bad re-assembly of the apperture mechanism. I recently cla'ed a Flektogon 2.8/35. The correct orientation of the apperture lever which was fastened by two screws was very critical there.

[mo]

Good news...I found some Zippo lighter fluid at the local Jewelers so I bought 2 X 125ml so I think I have a lifetime supply now...
I cleaned the blades it took quite a few wipes and cotton buds and they are now working.
I am amazed that almost invisible (I was not sure what I was looking for) grease can do this.
Thanks to everyone for their encouragement and links and "how to do" instructions.

[Tramis]

Hello guys! Sorry for bumping old thread, but I got this lens for free, but there is one part missing.