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Archive 2011 · Rokkor 58mm f1.2 conversion - question
  
 
safcraft
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p.1 #1 · Rokkor 58mm f1.2 conversion - question


I am adapting the Rokkor 58mm to Canon mount.

There are lots of guides with pictures around the net and quite detailed. However on my own conversion i found my lens behaves different.

There is an aperture lever that is pushed from the outside with some sort of mechanical mount in a minolta camera. This lever unlocks wide open default setting on my lens. That means i can change the aperture from f16 to f2 freely without touching this lever. The iris responds.

If i set the aperture ring to f1.2...it then stucks and stays there, unless i push the Aperture lever mentioned.

This is a picture of what i am talking about, it is not mine sorry for the copyright, took it from a guide website and inserted some text:






So my doubt is...must i dismount the lens to remove this mechanism?
If i dont, after EOS conversion i will not have this lever to close the iris. Even if i did i would have to unmount lens, push, mount lens.
No guide comments on this, despite all show this lever.

Any insight? Thanks




Jan 26, 2011 at 12:30 PM
pengland
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p.1 #2 · Rokkor 58mm f1.2 conversion - question


It sounds like there is some kind of resistance in the aperture mechanism that the spring can not overcome. This resistance is quite often caused by oil residue on the aperture blades and the nearby corresponding aperture cup surfaces. When the blades are in the wide open position they have the greatest amount of surface area "exposed" to oil and are therefore most likely to get stuck in this position. This is the reason that many old lenses appear to have their aperture blades "stuck" in the wide open position.
If oil is causing the sticking the lens will have to be stripped down and the aperture blades and aperture cup components will require cleaning.



Jan 26, 2011 at 01:55 PM
Cube1989
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p.1 #3 · Rokkor 58mm f1.2 conversion - question


My 58mm f1.4 was not sticking WO like that. Probably oil causing it to stick like pengland said.

Slowly remove parts of the lens and look for anything wrong, they are not very complicated to work on.

Have fun !



Jan 26, 2011 at 04:56 PM
safcraft
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p.1 #4 · Rokkor 58mm f1.2 conversion - question


The blades do not seem sticky at all. Seems more like some other sort of mechanical issue, it really does seem intended ! As if the lever is there for that reason only.
Otherwise what does it serve?

I will dismount it even further, to see what i can find.
Thank you



Jan 27, 2011 at 10:53 AM
pengland
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p.1 #5 · Rokkor 58mm f1.2 conversion - question


The pin or lever you have indicated on the pic is connected to the mechanism on the original lens back designed for use on Minolta cameras. It is not used once the lens has been converted to EOS. It was not designed for direct manual operation of the aperture.

When operating the aperture ring, is your lens sticking in the wide open position only when the lens back is installed or is it also sticking with the back off?



Jan 27, 2011 at 01:33 PM
Cube1989
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p.1 #6 · Rokkor 58mm f1.2 conversion - question


When you pull the aperture lever, the lens should stay wide open at any aperture selected.

When the lens is not mounted on a camera, this lever is not pulled and lens will change aperture when you turn the aperture ring.

If you plan to convert the lens to EOS, you will probably need to cut the aperture lever.

I hope I understood the problem correctly.



Jan 27, 2011 at 05:05 PM
safcraft
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p.1 #7 · Rokkor 58mm f1.2 conversion - question


When i operate the aperture ring, with the lens OFF the camera, it sticks when i put it in f1.2. Only in f1.2 and not in either aperture. Blades seem ok and snappy.

Also, if the aperture lever is pulled , the lens also stays open and stays there when the lever retracts to its position.

With the back ring off (like in the picture) one can see that the lever pushes the mechanism and makes a small click when full depressed. This click retains the blades in Wide Open This really looks like it is intentioned, or dued to some other reason, the lens may have been opened before and mounted improperly!?

I hope it doesnt sound too confusing...
I will try to take pictures in the weekend.
Thanks



Jan 27, 2011 at 05:33 PM
 

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debuggerus
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p.1 #8 · Rokkor 58mm f1.2 conversion - question


It seems like the aperture guide (Aperture control tang & slot ablove) might not be adjusted correctly. Next to the red arrow above, from the right, there are 2 screws. With the ring set at f1.2, loosen the 2 screws and adjust/slide the guide downward until the blades are wide open.


Jan 27, 2011 at 05:49 PM
Cube1989
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p.1 #9 · Rokkor 58mm f1.2 conversion - question


Something is probably wrong. Do you have pictures of your lens ?


Jan 27, 2011 at 05:59 PM
pengland
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p.1 #10 · Rokkor 58mm f1.2 conversion - question


Referring to your pic.....is the tang in the slot? With the lens back off and while operating the aperture control ring; are the tang and the attached brass ring rotating together?

The click you hear may be the blades and or the mechanism entering the "stuck" position. The return spring is responsible for moving the blades to "closed down" positions. This spring can only do this if the tension it applies can move the blades and mechanism and overcome any resistance to movement. If there is too much resistance to movement when the blades are in the f1.2 position they will stay in this position regardless of the position of the aperture control ring.



Jan 27, 2011 at 06:17 PM
safcraft
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p.1 #11 · Rokkor 58mm f1.2 conversion - question


Busy weekend, litle time to work with the Rokkor but....its working !!
I (lazy man) did not take pictures sorry, but somehow i got the blades to work.
You were all right, it was some kind of oil/dirt in the blades, i can see that now very clearly. It was probably due to lack of use for a long time.

The only bad thing was that i managed to press the litle ball bearing (aperture ring) too much and it is now too deep to make clicks. It is probably beyond repair as i guess the hole is deeper now. The ring rotates freely and it is more dificult to stop it at f1.2 or f1.6. It is possible with care though.

Thank you all, i now have to shave the midle ring a bit further because the lens is focusing up to 3m. I need a litle more than that. Because i want to use it in the 5D i will not to shave too much in order not to get mirror problems.
Cheers



Jan 31, 2011 at 09:23 AM
pengland
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p.1 #12 · Rokkor 58mm f1.2 conversion - question


safcraft wrote:
Busy weekend, litle time to work with the Rokkor but....its working !!
I (lazy man) did not take pictures sorry, but somehow i got the blades to work.
You were all right, it was some kind of oil/dirt in the blades, i can see that now very clearly. It was probably due to lack of use for a long time.

The only bad thing was that i managed to press the litle ball bearing (aperture ring) too much and it is now too deep to make clicks. It is probably beyond repair as i guess the hole is deeper now. The ring
...Show more

I'm glad to hear that you got it worked out. It sounds like you lost the spring that sits in the hole behind the detente ball. If you use a tiny drop of solvent (thin the grease) and a magnet you should be able to recover the ball. Put a tiny dab of grease in an upside down bottle lid or old rear camera cap and place the ball on the dab of grease for safe-keeping while you work on the lens. With some luck your missing spring may be somewhere under the aperture ring or inside the rear of the lens. It's worth a look. Also check in the area where you have been doing work on the lens. Sometimes a big magnet swept around the work area, floor., chair etc....is useful for finding such missing parts.
Good luck!



Jan 31, 2011 at 04:01 PM
safcraft
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p.1 #13 · Rokkor 58mm f1.2 conversion - question


There is a spring inside that tiny hole The ball is so tiny, the hole is tinier and the spring must microscopic!!
I will have a look! Thanks



Jan 31, 2011 at 09:53 PM
pengland
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p.1 #14 · Rokkor 58mm f1.2 conversion - question


The spring is tiny but the good news is that most people loose the ball first. You have to be ready for it when you lift off the aperture ring. The spring usually stays in the hole as grease usually keeps it there.

When you find the spring put it back in the hole and use a toothpick to apply a little lithium grease into the spring and onto the corresponding notches inside the aperture ring. Hold the lens steady with one hand with the aperture ring almost in place. Using either a magnetic screwdriver or the toothpick with a dab of grease (to act like temporary glue) on its end, pick up the ball and carefully place it on top of the spring. Using a small non-magnetic screwdriver or flat toothpick, press the ball down into the hole while compressing the spring while moving the aperture ring into place. You should now have your aperture click stops working again. Be careful not to lift the aperture ring until the lens back is back in position otherwise the ball will come flying out under spring pressure.....and you could end up on the hunt for the ball AND spring.



Jan 31, 2011 at 10:56 PM





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