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12-01-2008, 03:01 AM   #1
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Dismantling a lens - easy?

I have an SMC Pentax-M 50mm f/2 lens which has a bit of dust and a tiny bit of fungus on the inner lens.

I just bought a very nice (but a bit yellow) SMC Takumar 50mm f/1.4 lens so I can afford to ruin the f/2 (but I don't really want to obviously).

I'm keen to have a go at cleaning it myself. I've read several threads about using ammonia or hydrogen peroxide or home window cleaner among other products. I'm a techo by trade so am comfortable with tools and the need for dexterity.

Is it as easy as removing the 8 screws on the K/mount at the back? (the 5 larger screws on the flat surface and the 3 smaller ones on the round?)

Can someone give me a quick rundown on how to actually pull it apart?

I'd also appreciate opinions of the best cleaning agent to kill and remove the fungus and the dust particles. I was simply going to use lens wipes and the chemical. Bad idea or is that the usual way?

Thanks for any advice.

12-01-2008, 03:20 AM   #2
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Rear entry's a bad idea. Best to go in through the front. Insert any innuendo you like into that statement.

The the screws on the back simply hold the mount on. What you need to do is unscrew the filter ring nameplate. The bit with "ASAHI OPT. CO., JAPAN" on it. Use a rubber sink plug or similar for friction, if need be.

Under that should be some screws that hold the filter ring on. And that's about as far as I dared went.
12-01-2008, 04:30 AM   #3
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Cool thanks.

There are a couple of very thin cut outs on opposite sides of the nameplate, so I guess that's where they put the tool to unscrew it. I might try to fashion a tool using very thin stainless steel sheet, or possibly two jewellers screwdrivers clamped together in a "V" shape.

Failing that, the rubber plug will get a go. As I said, it's now an expendable lens and not too much use in it's current state, so nothing ventured.......
12-01-2008, 04:33 AM   #4
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I should add that I'll try and remember to take pictures of my effort. It will be interesting whichever way it turns out

P.S. I asked my wife if I should go in the back or the front and she said "Don't even think about going in the back", so I guess the front it is

12-01-2008, 04:48 AM - 1 Like   #5
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QuoteOriginally posted by lithos Quote
What you need to do is unscrew the filter ring nameplate. The bit with "ASAHI OPT. CO., JAPAN" on it. Use a rubber sink plug or similar for friction, if need be.
Before you start, get the right tools! It will make it a lot easier and you'll be less likely to lose something or do any damage. Also, take lots of photos as you work. Firstly, it means that you'll be able to provide a tutorial (<g>) and secondly, you'll have them as a reference when you reassemble the lens.

It's best to get some latex gloves, you can get a big bag of them cheap from a hardware store. Wearing gloves means that you don't get finger prints on the lenses. To unscrew the name plate I found that the best thing was an M42 rear cap covered in a latex glove. This means that the latex covered rim of the cap is in contact with the name plate and the front element is not touched. The name plate screws into the filter ring, so if there is a dent in the filter ring you have to do something about that first. You may find it useful to clean the filtyer ring with a toothbrush or a stiff artists paint brush first. This will clean out any crud in the threads and make unscrewing the name plate easier.

The name plate can be stiff. Recently I took apart an almost mint Super Takumar (it was unused except for the fungus that I needed to remove) and it took quite a bit of force to get the name plate to move (I guess it had not been moved in 40 years). So it is important not to use a method that could mean touching the front element.

QuoteQuote:
Under that should be some screws that hold the filter ring on. And that's about as far as I dared went.
The screws are very small, so be very careful not to lose them. They are also a real pain to get back into place and there are various techniques people employ - magnetic screw drivers, a bit of grease on the screw head etc. I used tweezers and carefully pushed the screw in place.

I don't know what the M50/2 is like inside. The Super Tak I cleaned was a 28mm and the front group was screwed in. (On my M50/1.4 it appears that there is a ring that secures the front element.) The fungus I wanted to remove was in the front group, so I unscrewed it, and made sure that the rest of the lens was covered to keep out dust.

To disassemble the front group I had to unscrew a ring. This one had indents in it. If you see a ring like this, you should use a lens spanner wrench to unscrew it. That is the safest way. Unfortunately spanner wrenches are $20 or $30 so you are now talking about a specialist investment. You can use a screw driver in the indent, but since you will have to use some force, you do risk the screw driver slipping and scratching something. To mitigate this risk I put a micro-fiber lens cloth over the lens and then put my thumb on the lens near where the screw driver will be - if I was going to scratch something it would be my thumb! <g> In fact. holding it like this, the force is away from the lens surface. However, in my case, the couple of times the screw driver slipped it scratched the edge of the lens. With a wide angle lens the edges of the elements are painted black, so I had to do some touching up later with a sharpie. I don't think you'll have that problem with a 50. As I said, if you get a spanner wrench you'll save yourself that problem. If you use screw drivers you will also scratch the ring. Remember that flare is caused by reflections inside the lens, so when you have reassembled the lens use a black sharpie (or a fine tipped fiber tipped pen) to remove the scratches. Be careful not to get the ink on the lens surface, but you do not want any shiny scratches inside the lens.

Once I had taken the group apart I got access to the fungus. Now the fun begins. Make sure that any element that you remove you keep in a clean place, on a pec pad (and covered) and that you know which way up it goes. I put a sheet of A4 white paper on my desk away from where I am working and put on it the pieces in the order I remove them, each one face up. I also use rear end caps to hold any screws I remove.

Search the internet for advice on what to use to clean off the fungus. Different people recommend different cleaning agents. I used denatured alcohol (90% ethanol, 10% methanol), it worked fine for me, but you have to decide what is best for you. The lens coasting is quite robust, but you do not want to scratch it with anything, so use clean lens cloths. Patience is important. I used a pec pad to apply the liquid, and then gently rubbed it off with a dry pec pad. It took me about 20 minutes to remove all the fungus. (I looked obliquely across the lens surface to check.) After that, I reassembled the lens, blowing it frequently with my rocket blower.

So here's what you need to get:

- good jeweller's screwdrivers
- fine pointed tweezers
- latex gloves
- spanner wrench
- magnet, just in case you drop a screw on the floor
- lens cloths, micro fiber, pec pads.
- cleaning fluid
- toothbrush

You'll find that there is a lot of advice on the forum.manualfocus.org forum.

As always, let us know how you do, and if possible post some before, during and after photos.

Richard

Last edited by richard64; 12-01-2008 at 03:40 PM. Reason: Opps gave the wrong url
12-01-2008, 05:35 AM   #6
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I have read that good old-fashioned lady's cold cream is used for removing/killing fungus. You might want to independently google that to verify.
12-01-2008, 06:17 AM   #7
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This page helped me a lot when I was pulling apart my fifty. Not the same lens but you get the general idea.

Forgot to mention that once you get the "name plate" off it's quite easy to do the rest.

//jim

Last edited by Jimfear; 12-01-2008 at 06:22 AM. Reason: Alzheimer light...
12-01-2008, 06:30 AM   #8
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Of course. It's putting it back together, and having it work that's hard.

My brother once disassembled his Petri SLR lens to fix it, then couldn't.
When he brought it to the Petri authorized repair shop they said they had never seen one taken apart that far!

IIRC Eric says he uses ordinary Windex to safely clean lens elements and kill fungus.

Chris

12-01-2008, 06:38 AM   #9
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Thge yellowing of the Takumar is fairly well documented. The glass is slightly radioactive, and this is what caused it to discolour.
The cure for that is to shine UV light through it for a period of time until the yellowing goes away.
IIRC, it can take a few weeks.
It doesn't require disassembly of the lens.
I believe a blacklight is recommended, and by coincidence, I saw that they are now available as compac florescent.
The cold cream for killing fungus thing is apparently true, although it is possible that what is really doing the job is whatever detergent is being used to remove the cold cream.
12-01-2008, 06:47 AM   #10
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Do you see any bad performance in the images?
if the answer is NO then do not crap your lens.
Otherwise the tutorial in how to dissasemble the 50/1.4 that was posted before is great, i used it to dissasemble a 135/3.5 only to have it fall on the floor and break a few days later
12-01-2008, 07:40 AM   #11
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Does anyone know how to rid of fungus within a group itself? i.e. no spanner indents, just pure cemented glass. I always get stuck at that point.
12-01-2008, 07:47 AM   #12
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QuoteOriginally posted by noel Quote
Does anyone know how to rid of fungus within a group itself? i.e. no spanner indents, just pure cemented glass. I always get stuck at that point.
If it has infected a cemented group, the only way to rid yourself of it is to split the lens group, clean the elements and re-cement the group.
Lens groups used to be cemented with an adhesive called Canada Balsam (I presume this indicates the source of the material), presumably because it is optically neutral.

Probably it's easier to find a lens of the type you are repairing with some other problem than fungus and disassemble it for the lens group you need.
12-01-2008, 08:23 AM   #13
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One really important thing is the screwdrivers you use. Most lenses use JIS screws. These are not the same as phillips (although they appear to be). They are actually crosspoint screws. Phillips screwdrivers will not exactly fit and will tend to strip the top of the screws.

Get a set of high quality JIS screwdrivers. Here is a set I bought which I am very happy with:

HOZAN JIS Screwdriver Set (2 drivers)
12-01-2008, 08:25 AM   #14
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I have used MEK (methy ethyl ketone) to clean fungus from lenses. It works really well. You can get it from painting supply stores (it is used as paint remover, so be careful what you get it on.)
12-01-2008, 04:11 PM   #15
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There's a guide to disassembling the f1.4 50 Super Tak here:

Disassembly and Cleaning of the F1.4 50mm Super Takumar Lens

I think, up until the A series, Pentax lenses were constructed in more or less the same way.

Those two slots on the retaining ring around the front lens take a specific sort of spanner - it's like a set of Vernier callipers, with the points of each "jaw" fitting into the slots. Think of the retaining ring as a slothead screw that's interrupted by the front lens element.

Apparently, the right tool for this can be made from a cheap set of Vernier callipers - just file the points down thin enough to fit in the slots. Might need to temper them to make 'em stiff enough to not twist when you're using the spanner.

And, for the love of god, make sure you cover the front element with something to protect it. Slather a heap of Blu-Tac on it or something.
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