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02-13-2013, 03:21 AM   #1
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Fine Mechanics [Aperture Construction]

Hello my dear friends, Im a new member here on PF, although i've been here doing research earlier! Since im a Swede, i want to start off by excusing for my lack of proper english grammar, and hope that you can understand what i mean!

My first thread is going to be about how the aperture works, and how it's constructed inside the lens!

The thing here is that i bought myself a very cheap lens, a RMC Tokina, 28mm f/2.8 whose aperture had stopped at full opening (f/2.8),
and since im very keen on learning how stuff works and most of all, how to repair them, i set off in order to try to repair the problem with the stuck aperture!

I now have the lens taken apart, all the glass is out from the tube, and left on the barrel is the aperture-mechanics and the focus-ring!

The problem that i now have, is trying to figure out how the little pin that is sticking out in the back of the lens-mount is gonna be able to regulate the aperture-opening!
I tested on one of my other lenses, and when i push that pin, it opens up the aperture inside the lens, but no matter how much i try, i cant figure out how the "lens-mount-part" is going to be fitted in order to work properly!

Is there someone here that has opened up a lens before, and know's how i should attach the aperture-linking in order to get it working properly again!

There are two spokes that iv'e found, one is normally bound to the aperture ring, and the other one seems to have the task of opening up the blades again!

As i said, im sorry that my english isn't very technical, but i hope that you understand what i need help with?

The very best of regards,

// Daniel

02-13-2013, 04:46 AM   #2
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I love hearing what the insides are made of and some pictures would really help along with your description. Good stuff, keep going!
02-13-2013, 05:55 AM   #3
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Indeed! Im gonna try to take some photos for you later on, i just need to borrow a lens from my roommate for that shoot!

I'll keep you posted with pics later tonight!
02-13-2013, 09:23 AM   #4
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Okey guys, now comes some fun stuff, and by that, i mean video-time!
Im having a cold at the moment, so excuse me for mumbling some times!


I want to point out that in my head, the pin on the mount should work "the other way", at least that's what my minds tell me :S Is it works now, there are two pins that can open up the aperture, but nothing that closes it again!

Enjoy!

02-13-2013, 09:28 AM   #5
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I should point out that all of the glasses isn't removed, it's just the last part that i refitted in order to keep things in order, and to remember how it was built together!
02-13-2013, 10:35 AM   #6
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Nice video! The blades have oil on them and can't move the way they are designed to. I'll post some photos in a few minutes that might help.
02-13-2013, 10:58 AM   #7
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Awesome! Yeah, iv'e done some removing of oil already, but there seems to be more to it than just that, i mean, what part of the construction is in charge of closing the blades?
02-13-2013, 11:03 AM   #8
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I have a Tokina that's slightly newer than your lens, so I used it for these photos. Here are the aperture blades from the back. Yours should be clean like this:



Here is the mount mechanism on mine. It's not the same as yours. The long brass finger is solid on mine. I don't know why. This part reaches into the lens and moves the blades:



The blades have another spring that makes them snap open and closed when the camera needs them to. You can see the chrome spring here.



You should get some solvent for the oil that's on the blades. Naptha works well, mineral spirits are OK, but the odorless type evaporates too slowly. Regulations on volatile organic compounds may limit what you can find. Remove the glass from both sides of the blades to keep the glass clean. Set the aperture ring to its highest f number (16 or 22). Use a cotton swab to apply the solvent to the blades, then work the blades open and closed. Then use another swab to wipe the blades. After a few tries, the blades should close on their own. If they don't close, look for trouble with the spring. Make sure the oil is completely gone before reassembly.

02-13-2013, 11:20 AM   #9
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Whoa, first of all, NICE pics mate!

Im gonna do as you say, and really get all that stinkin' oil out of there! You reckin it will close by itself after that?

By the way, it's really fun to take lenses apart, being gentle and systematic!

Alcohol (Pure alcohol, not whisky or that type), might that work or is it too harch on the materials?
02-13-2013, 11:21 AM   #10
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By the way, can you also see two pins that when moved on, effects the aperture blades?
02-13-2013, 12:56 PM   #11
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Hello again! Im very very pleased to let you know that i now have a perfectly working lens! I went over the aperture-blades 4-5 times with what we in sweden call "T-Röd", or "T-Red" in english, it's some sort of alcohol, and that seemed to do the trick!

It has been very good for my "fix-stuff-skills", i just wished more people, especially from my generation (late 80's), would learn how to fix stuff instead of just buying new ones!

Thanks a million Just1MoreDave, you helped me a lot!
02-13-2013, 08:37 PM   #12
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Excellent. Now let's see if I can get mine back together again... there. I like this lens.

The K-mount spec has two ways to move the aperture blades. One is the aperture lever and the other is the aperture ring. I think the "two pins" you're seeing are those two mechanisms. I can see a black bar below the spring (deeper into the lens) in my 3rd shot that the contacts brass lever in shot 2. The aperture ring seems to move a different mechanism. There is no standard way of doing this; even Pentax seemed to do it differently for each lens.
02-14-2013, 03:00 AM   #13
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QuoteOriginally posted by Just1MoreDave Quote
Excellent. Now let's see if I can get mine back together again... there. I like this lens.

The K-mount spec has two ways to move the aperture blades. One is the aperture lever and the other is the aperture ring. I think the "two pins" you're seeing are those two mechanisms. I can see a black bar below the spring (deeper into the lens) in my 3rd shot that the contacts brass lever in shot 2. The aperture ring seems to move a different mechanism. There is no standard way of doing this; even Pentax seemed to do it differently for each lens.

Haha, yeah now that i've reasembled it again, im not scared of opening up more lenses! Once i understood that that tiny little spring was suppose to close the aperture, i felt much relieved, and understood that the tech. inside isnt't that "hardcore", it's all common sence!

Now i just need to find some more "broken" lenses that i can fix!
02-22-2013, 04:16 PM   #14
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evening blokes, came across this and everything seemed simple enough as I had the same problem with the aperture blades on my tokina 28mm (got that fixed!!! so many thanks for the thread but went a bit too far with disassembly and removed the focus ring and didn't mark off the point it came off the thread or how far to screw it back in..... tried a couple times but not really getting anywhere!! not sure if you went through this procedure with disassembly but if anyone has any idea of the correct positioning of the focus ring for reasembley it would be much appreciated!!!
02-22-2013, 04:25 PM   #15
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or if someone could take a photo of the lens fully extended and fully retracted I might be able to figure it out a bit easier, again many thanks in advance!!
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