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Aperture mechanism assembly
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PostPosted: Fri Mar 05, 2010 9:17 am    Post subject: Aperture mechanism assembly Reply with quote
Hello there,
First post in the forums! I am totally new to the manual focus lenses and yesterday I started my journey by opening one of them - hands on experience, right!

It is a Meyer Oreston 50mm f1.8.

I came to a point where I can't reassemble the aperture blades. There are altogether 6 blades and they are equal in length. If I put a blade on top of the previous one and do this for all blades, mechanism stuck in the end. What should I do?

Thanks for your help in advance and sorry for the picture quality - it is from my cell phone.


PS: Somehow, I can't link or embed the picture. In the preview mode it looks OK, but when I hit the submit button - the link/picture disappears or shows a broken link.

http://img69.imageshack.us/img69/4761/img00051w.jpg



PostPosted: Fri Mar 05, 2010 10:37 am    Post subject: Re: Aperture mechanism assembly Reply with quote
onur wrote:
Hello there,
First post in the forums! I am totally new to the manual focus lenses and yesterday I started my journey by opening one of them - hands on experience, right!

It is a Meyer Oreston 50mm f1.8.

I came to a point where I can't reassemble the aperture blades. There are altogether 6 blades and they are equal in length. If I put a blade on top of the previous one and do this for all blades, mechanism stuck in the end. What should I do?

Thanks for your help in advance and sorry for the picture quality - it is from my cell phone.


PS: Somehow, I can't link or embed the picture. In the preview mode it looks OK, but when I hit the submit button - the link/picture disappears or shows a broken link.

http://img69.imageshack.us/img69/4761/img00051w.jpg



Images are never displayed with a first post - it's an anti-spam prevention measurement!


PostPosted: Fri Mar 05, 2010 12:18 pm    Post subject: Re: Aperture mechanism assembly Reply with quote
onur wrote:
Hello there,

I came to a point where I can't reassemble the aperture blades. There are altogether 6 blades and they are equal in length. If I put a blade on top of the previous one and do this for all blades, mechanism stuck in the end. What should I do?

Thanks for your help in advance and sorry for the picture quality - it is from my cell phone.

Hi onur, welcome.

You're going to have to take all the blades off and start again, sorry. First place the pin of the first blade in its recess and swing it back so that it's wide open, not closed as in the picture. Now work round clockwise (I think that's right, but the next blade goes at the pin end of the first). After 3 or 4 you'll come to one whose recess is covered by the first blade. From here on you have to carefully lift up the end of the covering blade and slide the loose blade underneath it to locate in the recess.

It's very tricky and tries anyone's patience. Be as gentle and steady as you can, and if you can't do it first time, give yourself a break, calm down and start again! My first time took several tries and over a couple of hours! Smile


PostPosted: Fri Mar 05, 2010 1:13 pm    Post subject: Reply with quote
LOL - probably anything bad could have happened, happened in my first case! From loosing a spring to the escape of marble ball into my keyboard...

I spent nearly 10 hours on the lens to open-close-reopen-noclose-try-try-try-partlyclose-open-close circle Smile

Well most of that time was about the aperture mechanism; but I was able to fix it before reading the Peter's response. I basically reinvented the wheel - it was exactly as Peter described.

Anyways, finally everything is worked out and the lens' interior is in much better condition than I started.

One more question though, I used very thin and small amount of machine oil on the helicoid (?) - is it OK? I believe there was some old grease there, now it is a mixture Smile

Couple of pics:



PostPosted: Fri Mar 05, 2010 1:58 pm    Post subject: Reply with quote
onur wrote:
One more question though, I used very thin and small amount of machine oil on the helicoid (?) - is it OK? I believe there was some old grease there, now it is a mixture Smile

No, this isn't a good idea. There is a danger the oil will run onto the aperture blades, especially when the lens is warm in the sun or in a glove box etc. If this happens they'll work too slowly or even become completely stuck. The blades should always be free of any lubricant.

You need to thoroughly clean off the oil and old grease on both parts of the helicoil with lighter fuel and Q-tips. Then relubricate it with a grease which has constant viscosity through a wide temperature range. Not all greases are suitable, you need to check this on the container. I use white lithium grease.

Glad to hear you fixed the blades! Smile
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