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10-30-2014, 10:44 AM   #1
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Revuenon 55mm f1.2

Hello, I have purchased a 55mm F1.2 Revuenon on ebay, the lens is in very good condition and the price was right but the aperture is stuck open. I know it's how to use these lenses butI have owned such a lens before and know that it is really sharp and want the option. It seems to be a common problem on these lenses and I've read that someone here has repaired it and was wondering if anyone has any tips and hints about what is wrong.
Thanks in advance greetings Sverker

10-30-2014, 10:48 AM   #2
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Hey, maybe this will help?
https://www.pentaxforums.com/forums/54-pentax-lens-articles/110657-how-use-me...k-x-k-7-a.html
10-30-2014, 10:55 AM   #3
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Thanks/it is a k lens and the aperture is broken/stuck
10-30-2014, 11:28 AM   #4
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Just to clarify -- it is stuck when it is NOT mounted on the camera? i.e. if you set it to f/16 unmounted, it is still wide open? (And moving the aperture lever doesn't do anything?)

The reason that needs clarification is because when it is mounted, it is supposed to stay open and not everybody knows that when getting an old manual lens. (It will only stop down in M mode and if your settings on the body are set properly for manual lenses -- see the above link).

10-30-2014, 11:31 AM   #5
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The Cosina 55/1.2 is pretty easy to disassemble from the front. Focus to 0.6m and find a tiny grub screw on the barrel. Loosen that and the barrel unscrews. Then the front lens group unscrews and you can access the front side of the aperture blades. Oil may have caused them to stick open. Naptha or mineral spirits will dissolve the oil enough to move the blades. Several repetitions is enough to get them working. Sometimes it's useful to take apart the rear, enough to remove the rear glass and see the back of the blades.

I'm not sure if the Cosina is constructed like the Revuenon.
10-30-2014, 11:32 AM   #6
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QuoteOriginally posted by Just1MoreDave Quote
I'm not sure if the Cosina is constructed like the Revuenon.
They are the same lens, pretty sure.
10-30-2014, 11:46 AM   #7
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Okey
The diaphragm does not move even when you hold it in your hand and turn the aperture ring. This is the 4 Revuenon 55mm F1.2 lens I have owned so I know how they usually works.....and I have/had a lot of mf lenses....
Somwhere in this forum I read that someone could fix this.....

---------- Post added 10-30-2014 at 11:55 AM ----------

OK thanks l had hope that it was something that had loosen on the bayonet side....the lens looks like new whith very little dust so I maybe will use it as it is for now...... I have the k 55 to use stopped down.


Last edited by Zeeke; 10-30-2014 at 12:01 PM.
10-30-2014, 12:52 PM   #8
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Ah, sorry, didn't know. Thing is, we often get problems with people using a manual lens in Av mode, which never stops the lens down. You need M mode for the camera to even try stopping down the aperture, and the Aperture ring must be Enabled in the Menu (also, no auto-ISO). But if you have these bases covered, the problem might be the lens, as you suspected. I can't help you further, but maybe you can find more leads here:
Revuenon 55mm F1.2 MC Lens Reviews - Miscellaneous Lenses - Pentax Lens Review Database
Cosina 55mm F1.2 Lens Reviews - Cosina Lenses - Pentax Lens Review Database
10-30-2014, 01:40 PM   #9
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If it is oil or grease that has make the blades stick whide open maybe a little warmth will make them wake up.
You have too excuse my bad English..... but I do understand better then I write....
10-30-2014, 07:39 PM   #10
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i dont know the lens but does it have auto-pin
10-30-2014, 11:02 PM   #11
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It is a K- mont and has the stop down lever.
10-31-2014, 03:48 AM   #12
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I am relay impressed bye the whide open sharpness and contrast off this lenses. Better than the Pentax m 50 f1.4 and the fa 50f1.4.
10-31-2014, 04:38 AM   #13
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QuoteOriginally posted by Zeeke Quote
I am relay impressed bye the whide open sharpness and contrast off this lenses. Better than the Pentax m 50 f1.4 and the fa 50f1.4.
Could you post some photos please ? Like 1.2 version of the same image from Revuenon and then wide open the same image from your other 2 fast 50mm lenses ? That would be much appreciated I think by many
10-31-2014, 07:35 AM   #14
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Okay I try to do that but I have already sold the Fa....... I am a little afraid to show som tests here there always someone ho will criticise the details...........

---------- Post added 10-31-2014 at 07:44 AM ----------

I have owned and own a lot off 50mm lenses and the best off the cheap one's is Olympus OM 50mm f1.8(sorry Pentax m 50mm f1.7).......
10-31-2014, 08:26 AM   #15
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Here is a sample from my copy of the lens...

It has the best bokeh I've seen, although this is a subjective opinion! From f/5,6 and smaller it is razor sharp like all the old manual well built 50mm Pentax lenses.
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