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Porst/Cosina 55mm f/1.2 - Aperture not moving
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PostPosted: Wed Jan 04, 2017 6:41 pm    Post subject: Porst/Cosina 55mm f/1.2 - Aperture not moving Reply with quote

Just picked up a Porst 55mm F/1.2 from garage sale. Got it dirt cheap as the aperture does not move when turning the ring.

Still, the aperture blades moves just fine when pushing the aperture preview levler.
I took a look inside the mechanism, and from the look of it, I feel that some of the mechanism may be missing?
The black ring is only connected to the aperture ring, and nothing else. Is there supposed to be an extra part, like a spring or something?

Please take a look at the pictures:


#1


#2


#3


#4


PostPosted: Wed Jan 04, 2017 8:15 pm    Post subject: Reply with quote

The pictures show the lens uses a similar mechanism as the Nikkors for example. With Nikkors the ring that moves the lever of the aperture inside the lens has a slot or groove (because the aperture mechanism has to turn both ways), this has to fit precisely into the lever. Failing to do so you can turn the aperture ring but the aperture does not move. Basically, the two parts must be connected, if the lens is a preset one there is not necessary a spring. Looking at the pictures, the silver ring has a spring loaded part.

Does the part at 10 o clock on the black ring on picture 2, fit into the slot on picture 3 that is at 2 o clock? Does the black ring turn as you turn the aperture ring?
Tomas


Last edited by tomasg on Wed Jan 04, 2017 8:30 pm; edited 1 time in total


PostPosted: Wed Jan 04, 2017 8:27 pm    Post subject: Reply with quote

Cant answer the problem itself,not familiar with the Lens,but,please,Remove the Optics when working on the 'bits'.Save yourself from grief Smile


PostPosted: Wed Jan 04, 2017 8:44 pm    Post subject: Reply with quote

My thought was that, on the black ring, the arm is supposed to fit into a slot, but there are no slots available for it to fit in to.
The arm just sits there in the air, not connected to anything.
The slot you see on (3rd picture) upper right corner is for the DOF preview arm on the silver colored ring, so no luck there.


PostPosted: Wed Jan 04, 2017 8:48 pm    Post subject: Reply with quote

tomasg wrote:

Does the part at 10 o clock on the black ring on picture 2, fit into the slot on picture 3 that is at 2 o clock? Does the black ring turn as you turn the aperture ring?
Tomas


No, it does not fit. That slot is for the DOF preview arm on the silver ring Sad
But yes, the black ring moves as I turn the aperture ring, but only that and nothing else.


PostPosted: Wed Jan 04, 2017 9:33 pm    Post subject: Reply with quote

I have taken this lens apart and managed fixed the aperture control issue. I can confirm this is indeed caused by a faulty spring issue.
However, DO NOT be tempted to fix the lens unless you know what you are doing!

As a consequence of taking everything apart, my lens is now misaligned and the aperture is no longer in the right position. Also, I am not confident that infinity focus is set optimally.

If you are taking it further, make sure to take many notes (take a movie clip of every step) and to mark the position of the aperture ring, the metal ring between the focusing ring or focusing hellicoid and aperture. Also watch out not to loose the tiny ball bearing inside the lens body which makes that clicky sound when you turn the aperture ring.

You will need some spare springs before embarking on this repair task. Something like these.
http://www.ebay.ie/itm/Expansion-Spring-Various-Sizes-Tension-Extension-Expanding-Extending-Springs-/152095086543?var=&hash=item236992d7cf:m:mDxbdJhTG4_CU3cfZ_dWBew

Good luck with it!


PostPosted: Wed Jan 04, 2017 9:36 pm    Post subject: Reply with quote

Eplejus wrote:
tomasg wrote:

Does the part at 10 o clock on the black ring on picture 2, fit into the slot on picture 3 that is at 2 o clock? Does the black ring turn as you turn the aperture ring?
Tomas


No, it does not fit. That slot is for the DOF preview arm on the silver ring Sad
But yes, the black ring moves as I turn the aperture ring, but only that and nothing else.


You know what? I think maybe there is nothing wrong with the lens or the mechanism. What happens if you push down and hold the dof preview and turn the aperture ring at the same time? I think you have to find a way of keeping the dof preview engaged all the time to be able to open/close the aperture with the aperture ring. Similar to what you have to do with the pin on some m42 lenses.


PostPosted: Wed Jan 04, 2017 9:38 pm    Post subject: Reply with quote

tomasg wrote:
Eplejus wrote:
tomasg wrote:

Does the part at 10 o clock on the black ring on picture 2, fit into the slot on picture 3 that is at 2 o clock? Does the black ring turn as you turn the aperture ring?
Tomas


No, it does not fit. That slot is for the DOF preview arm on the silver ring Sad
But yes, the black ring moves as I turn the aperture ring, but only that and nothing else.


You know what? I think maybe there is nothing wrong with the lens or the mechanism. What happens if you push down and hold the dof preview and turn the aperture ring at the same time? I think you have to find a way of keeping the dof preview engaged all the time to be able to open/close the aperture with the aperture ring. Similar to what you have to do with the pin on some m42 lenses.


Ah, mistery solved thanx to stingOM


PostPosted: Wed Jan 04, 2017 9:59 pm    Post subject: Reply with quote

Sadly, that diden't work either. Already tried that before I opened the lens. Sad


PostPosted: Thu Jan 05, 2017 2:15 pm    Post subject: Reply with quote

Problem solved! Turned out, the previous owner had installed the gold plated ring in wrong position.
The slot was fitted over the DOF-preview arm instead of the arm on the black aperture control ring.
The aperture work flawlessly now.

Now for fixing the next problem. Infinity focus is way off...but this may be due to the adapter ring I'm using.
(K&F PK-FX adapter on a Fuji X-T1)


PostPosted: Thu Jan 05, 2017 5:13 pm    Post subject: Reply with quote

Eplejus wrote:
Problem solved! Turned out, the previous owner had installed the gold plated ring in wrong position.
The slot was fitted over the DOF-preview arm instead of the arm on the black aperture control ring.
The aperture work flawlessly now.

Now for fixing the next problem. Infinity focus is way off...but this may be due to the adapter ring I'm using.
(K&F PK-FX adapter on a Fuji X-T1)


Glad that you solved the problem!