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12-30-2010, 01:22 AM - 1 Like   #1
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Maybe too technical... Takumar help

A while back I found myself a good deal on an old Super Takumar 28 3.5. Poor little lens wouldn't focus anymore, and had a bit of fungus starting to take root.
Sensing a fun project, I pulled the thing apart and cleaned it up.

I found a diagram for the disassembly and reassembly of a 50mm Tak that got me close enough... but it was missing some important information. The little metal bar that limits focusing rotation had been knocked out of place (leading to an over-tightening, leading to focus and aperture locking up). Anyway, the long and short of it was, in the end I couldn't find any markings or pieces inside to line things up for re-assembly in order to assure proper focusing.

I put things back together by trial and error, and ended up with a working lens (figured out MFD, repeatedly dis- and re- assembled till it focused right). The thing is, though, the focusing scale is now off by about 1/2 inch. It's not a killer - the Kx will beep on focus confirm, and the focus on this lens is pretty forgiving anyway, especially once stopped down a little. It's become my go-to landscape lens, and a favorite of mine for other things as well...

Its just been bugging me, though - what is the secret to getting those helical focusing threads back together at the right point, so that everything focuses right, short of trial and error? What did I miss?

Thanks!
-Mike

12-30-2010, 04:17 AM   #2
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Hi there.....................Fun project......

...oooOOOooo...

No advise from me ..............

Enjoy ........

12-30-2010, 07:15 AM   #3
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If there's some sort of grub screws holding the focus scale in place - loosen these and re-orient the scale, then tighten again. I don't have mine handy to look at.
12-30-2010, 07:52 AM   #4
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QuoteOriginally posted by Nesster Quote
If there's some sort of grub screws holding the focus scale in place - loosen these and re-orient the scale, then tighten again. I don't have mine handy to look at.
'Fraid not...
The scale is printed on the lens barrel itself. I could move the aperture markings around, but...
Thanks though!

12-30-2010, 11:29 AM   #5
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There are two versions of the 28/3.5 and I've not had the chance to take either apart. Unlike the method of spinning off the name ring, some of the lenses have the entire outer shroud spin off to expose the element retainers as well as access the focus barrel. The trick is figuring out how to get the shroud off without too much force. Once off you will usually see the similar setup as the 50mm with the three screws and washers holding down the focus barrel. Try a hair dryer to heat the outside up a little, but not over cook. Wear a latex glove for extra grip.


Last edited by MysteryOnion; 01-01-2011 at 01:56 AM.
12-30-2010, 11:37 AM   #6
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QuoteOriginally posted by MysteryOnion Quote
There are two versions of the 28/3.5 and I've not had the chance to take either apart. Unlike the method of spinning off the name ring, some of the lenses have the entire outer shroud spin off to expose the element retainers as well as access the focus barrel. The trick is figuring out how to get the shroud off without too much force. Once off you will usually see the similar setup as the 50mm with the three screws and washers holding down the focus barrel. Try a hair dryer to heat the outside up a little, but not over cook. Where a latex glove for extra grip.
This one had the little name ring spin off - it's the larger of the two 28/3.5 models. I've gotten it back together and focusing right... but I'm just wondering if there's a standard set of markings to getting the focusing threads back together in the right spot, or a trick to it.

I had to end up using trial and error - setting up a tape measure and setting focus close till it was within tolerable. It still focuses a little past infinity, if I'm not careful.
12-30-2010, 01:11 PM   #7
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Usually a colliminator is untilized for infinity. It is set up to optically find infinity and I guess that once the screws are in place, they don't leave a mark.
check this out
http://www.kyphoto.com/classics/collimator.html

Last edited by MysteryOnion; 12-30-2010 at 01:40 PM.
12-30-2010, 04:24 PM   #8
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QuoteOriginally posted by MysteryOnion Quote
Usually a colliminator is untilized for infinity. It is set up to optically find infinity and I guess that once the screws are in place, they don't leave a mark.
check this out
Test Equipment / Collimator
Hm... that would make testing the lenses easier than my whole "measuring tape and eyeball" method. Certainly an interesting read!

What you're saying, though, is that there's no little guide markers or calibration lines or anything within the lens to help with aligning the focus barrel in the helical threads?


I already have a working lens... I'm just trying to find an easier way if I have to do it again...

*Edit*
I think I just realized how that collimator is supposed to work... More useful than I thought.

Second question, then - on the two lenses I've pulled apart and put back together (this one, and a sears 135/2.8), actually pysically getting the focusing threads to re-mesh was a PAIN in the tuckus. Anyone have a trick for that?


Last edited by sgtkashim; 12-30-2010 at 07:40 PM. Reason: Flash of light from above
12-30-2010, 10:16 PM   #9
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I have found that it is a sort of trial and error if I don't note the position prior to separation of the parts. If you know before hand that the helicoid is 3/5th turns then you can land it if you noted the starting point. I did put a tamron 28-80 back together and noted a mark to the starting point for assembly. An exception than a rule I would think as with my SMC 50mm/1.4 had no marks and was a dual helicoid I was left to guess.
12-31-2010, 11:59 AM   #10
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Most Takumar and K lenses were designed so that you didn't need to put the helix back together exactly the way it was. You just need a collimator to set infinity when you put it back together. You'll just have to use trial and error and your in-camera AF sensor to bring things in. On lenses that require you to put the helix back the same way you need to choose one of the threads of the helix and mark the male and female parts so that you can align them when you put things back together. Some lenses are a megapain to deal with as has already been mentioned.
12-31-2010, 01:37 PM   #11
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QuoteOriginally posted by pentaxus Quote
Most Takumar and K lenses were designed so that you didn't need to put the helix back together exactly the way it was. You just need a collimator to set infinity when you put it back together. You'll just have to use trial and error and your in-camera AF sensor to bring things in. On lenses that require you to put the helix back the same way you need to choose one of the threads of the helix and mark the male and female parts so that you can align them when you put things back together. Some lenses are a megapain to deal with as has already been mentioned.
Thanks!
I guess I'll see if we have any broken binoculars around... and go in to the next one with a little more planning!
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