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Mamiya SX Lens Aperture Ring Removal, etc.
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PostPosted: Tue Jul 13, 2010 10:11 pm    Post subject: Mamiya SX Lens Aperture Ring Removal, etc. Reply with quote

Hi All,

Apologies if this is covered elsewhere; I searched and couldn't find the information.

I'm considering modifying the aperture rings of a couple of Mamiya SX lenses to remove the problematic lip. So I'm wondering how to remove them.

I notice that if I rotate the aperture ring, there's a position where three small phillips-head screws are revealed through the three slots in the ring (looking from the back). Am I right in assuming that unscrewing them will enable me to lift off the mount, and remove the aperture ring?

And a followup question: once I'm inside there (assuming the foregoing procedure is correct), is it a straightforward matter to disable the auto-aperture pin with the usual coffee-stirrer/cotton-swab technique?

Thanks for your help!

Cheers,

Jon


PostPosted: Wed Jul 14, 2010 1:21 am    Post subject: Reply with quote

Hi Jon,

One way I have done this is by sanding down adapter on the outer most edge all the way round, making the diameter of the adapter fit inside the protruding lip of the aperture ring.( I seen others sand the outer edge in an angle).It worked for me and of course you already mentioned the disabling the auto diaphragm method- works great.

Regards


PostPosted: Wed Jul 14, 2010 1:41 am    Post subject: Reply with quote

Hi,

Thanks so much for the reply.

I should have been clearer: I would be using these lenses on a Pentax K20D via M42->K adapter. Since the adapter is flush with the camera's lens mount when installed, do you think it will be enough simply to file the lip flat with the lens mount, without angling the edge? I don't need the aperture ring to fit inside an adapter - just to sit flush with it.

And am I right about the three screws? Is that the way to remove the mount?

Thanks again,

Jon


PostPosted: Wed Jul 14, 2010 1:55 am    Post subject: Reply with quote

Jon,

Yes it will work. If you look closely on the current lens mount of your Mamiya SX you will see that the inside groove of the aperture ring is a smidgen lower than the actual lens mount. So if you were to shave the outer perimeter of your M42 to K mount Adapter to fit inside the aperture protrusion , you will be able to move your aperture about freely-it seems to fit just right. And you are right about the three screws to remove the backend .


Quote:
I don't need the aperture ring to fit inside an adapter - just to sit flush with it.


Its the other way around here "the adapter has to fit inside the aperture ring" - after you shaved the outer perimeter. I hope it works for you. Again I have seen some shave it at an angle.



cheers


Last edited by Kathmandu on Wed Jul 14, 2010 2:16 am; edited 1 time in total


PostPosted: Wed Jul 14, 2010 2:13 am    Post subject: Reply with quote




This is the lens mount end of the Mamiya Sx 55mm f1.4 .
1. This is the aperture ring that protrudes up higher than the back of the lens mount as we know.

2. Is my suggested circumference for your M42 to K mount after shaving all around.

3. If you look closely you will see that this spot is higher than 4 which allows the modified adapter to sit flush with your camera and still give free movement to the aperture ring.

I am assuming all SX lenses are the same in these ways- hence my suggestion.

I hope my illustration helps in some way.


NOTE: Your idea of filing the lip down should work,too!- I am sorry I did not get that from reading your first post. Had a long day. You wouldn't be doing any irreversible damage to the lens if you do the modifications to your adapter, of course.


Cheers


PostPosted: Wed Jul 14, 2010 5:13 pm    Post subject: Reply with quote

Thank you so much! That is tremendously helpful, and uncommonly thoughtful of you - just the information I needed.

I think I may now have the courage necessary to tackle this project.

Thanks again!

Cheers,

Jon


PostPosted: Wed Jul 14, 2010 8:11 pm    Post subject: Reply with quote

Thanks Jon,

It would be nice to see some sample images once you have it mounted on your PentaX. They are excellent quality lenses.


Cheers


PostPosted: Fri Jul 16, 2010 8:31 pm    Post subject: Reply with quote

Absolutely! Just let me say that it may be a while - I don't own a lathe, so I'm trying to figure out a way to rig my Dremel to take off the excess metal neatly. (I know my hands aren't steady enough for such delicate work.)

Cheers,

Jon