Please help

Hi Dave, i read the article and tried stop down metering and DoF preview method. If I have not done wrong then none of them worked as no matter what the aperture was, the metering gave me the same shutter speed. DoF preview method showed the same exposure bar for all apertures. However, when I connect the lens with a teleconverter or extension tube, the aperture seems work. Thanks for the link. I will try to show my lens to a service centre and see what they suggest.

Algi thanks for the thread link. I have read 4 pages and it seems like comparisons among different f1.2 lenses. Nobody has mentioned similar problem. Thanks to all of you who commented here.

I just found a difference between Pentax M and Porst. When lenses are unmounted and I move the aperture ring, in Pentax M aperture lever moves with aperture ring. But in Porst the lever (only the lever, internal blades move) is stuck in the same position. Also in Porst I can easily move the lever with my finger but in Pentax M the lever only moves with aperture ring, feels hard to move with finger. Any idea?
My other Manual zoom 80-200mm lens' aperture lever also similar to my 50mm M lens
But my AF lens DA18-55 and 55-200 aperture lever is similar to Porst. Can this be the cause?

Sounds like the aperture lever on the lens should have a spring on it and its broken... Check the positioning of the aperture lever on your porst and compare it to your m lens and i imagine it will be in a totally different place. So when its attached to the camera the camera will try to move the aperture lever but the lever is in the wrong place and so cannot move the aperture blades.

Thanks for your reply. I am not sure but i think there is a spring on it and not broken. Because when i move the lever to different positions it comes back to its original position. Here is a video showing three lenses you can see 1st lens is Porst, 2nd lens is M 50mm and 3rd lens is AF 50-200.

link

While M lens is wide open (f1.7) its lever is completely in the opposite side (left side) of Porst wide open (right side, as you can see in the video). AF lens' lever is in the same position (right side) as Porst but I can see that the aperture blades are closed (DA 50-200 does not have aperture ring). So you were absolutely right. Is it possible to fix it by myself or should I go to a repairing shop? I am thinking to go to a camera repairing shop tomorrow.

When attached to the camera it should only stop down when you take a picture or you use dof preview.

Hi,
A couple of things to consider, it is possible that the back of the lens was opened at some time and on re-assembly the inner cam ring (if like the Pentax M) was returned in the wrong position. This would mean that changes to the aperture ring would not translate to the lever. The Pentax version has a notch that locates within the inner ring housing. As mentioned this cam is sprung loaded by expanding spring.

What does interest me is that it appears to work when mounted to a extension! Is it possible that the lever is shorter in length than the other lenses? The linked video looks as if this lever is stubby compared to the others. Probably the distance from the lens mount to the end of the lever is worth looking at.

Check out the many Youtube disassembly videos, they give a good insight as to what goes on inside.

Good luck..

Your Porst is the same as my Porst and I've just looked at
a Ricoh 50mm f/1.4 and that works the same as the Porst.
Only the Pentax lens has an aperture lever that moves as
you move the aperture ring... so I don't think that's the
fault the lever starts from the f22 position.

As a quick check put the lens at f2.8 and see if there is
about 3-6mm of free movement on the lever before it
engages and opens the aperture to f1.2

My lever sticks up 6.54mm

Perhaps someone can supply you with the address of a
Pentax lens repairman?..... I seem to remember someone
called Alan ? but haven't got his details.

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Just checked my 30 year old 55mm SMC Pentax lens. With the front element of the lens pointing downwards the lever is to the right at f22 and to the left when fully open. Turning the aperture ring moves the lever and vice versa. The best estimate I can make for the lever length is a little short of 7mm.

The repairer that Algernon mentions may be this guy -

http://www.alan49.x10.mx/index.htm

Dave

That's the man

The problem is solved automatically/magically(?)

That's what happened basically: I explained my problem to the man in camera shop. He went inside (back room) for 4/5 minutes then came back and told me the mechanism was fine... I saw the aperture was closing down properly when he clicked the shutter. He then checked my camera with his auto focus lens and my Pentax M lens. He asked me if I use manual mode for manual lenses.
He took couple of pictures with Porst. And... yes I can see the difference among similar pictures taken in different apertures. He said he had never heard of Porst. Also said the aperture working as it meant to be but he was not happy with the optical quality of the lens. I thanked him then came home and took a few pictures and yes Porst was working like my Pentax M.

CURIOUSLY I SET "APERTURE RING SETTINGS" TO "PROHIBITED" AND THE SHUTTER DID NOT WORK. SO, YES TODAY THE LENS IS WORKING AS IT MEANT TO BE AND COMMUNICATING WITH MY CAMERA.
I think I should have asked him what he did in the back room, did he change any setting in my camera or did he do anything to the lever.
I just remembered that I charged my camera battery fully last night. I know this does not have anything with the aperture problem but just thought to mention it.
Here two pictures one at f1.2 and the other at f8.
f1.2


f8



Thank you guys for so many suggestions and informative links.

Best regards,

Jalal

That's good to hear. It's a pity he didn't tell you
what (if anything) was wrong.

It should be sharper than the 2 pics you've posted, but
at least it's not suffering from flare. It's better to use
a lens hood to get slightly better contrast.

Excellent lens especially at the price you paid.

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I think the sharpness issue is user error.
I bought a lens hood and front cap on ebay since the lens came with a rear cap and UV filter.
The lens was a really good bargain

Regards,

Jalal

A Porst 55mm f/1.2 sold for £240 (posted) on ebay yesterday

It was cheap compared to a Yashica M42 version of more or less
the same lens which went for £688 (posted).... that one included
a free Yashica camera which wasn't worth very much

Like most Yashica's it didn't have the Auto/Manual
switch and pin removal is usually impossible.

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