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03-13-2013, 01:35 PM   #1
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Defects in Pentax-M 100mm f/4, fix or leave alone?

I got an M 100mm for a good price on Ebay with the seller saying it was "mint" and the pictures showing no major issues except when I received it today and examined it, it has some big defects inside the lens. See below: (Not the best picture of defect but best I could get)


It's like a smudge on the interior like someone cleaned it with grease on the inside.

However when taking photos I get various results that don't look like anything is really wrong with them:





The defect appears to be on the interior of the front element, I feel comfortable taking it apart (I practiced on a spare 50mm a few weeks ago for fun) but I don't know how to disassemble this particular lens or even if it is worth it since the pictures look okay.

Any advice would be nice, although I don't want to sell/return it because I got it for such a good price compared to the most recent auctions on the same lens (and those had advertised fungus/haze).

Thank you.

03-13-2013, 01:44 PM   #2
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I have a similar 'fogged' 100/4 macro, its in between the kitted elements, so, unless you know to separate the kitted elements, clean it, if it can be cleaned, and kit it again, I would accept the slightly lower contrast when bright lights hit the lens.
03-13-2013, 01:49 PM   #3
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I would clean the haze up (if that is possible) to see the colors.
03-13-2013, 01:53 PM   #4
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QuoteOriginally posted by glasbak Quote
I have a similar 'fogged' 100/4 macro, its in between the kitted elements, so, unless you know to separate the kitted elements, clean it, if it can be cleaned, and kit it again, I would accept the slightly lower contrast when bright lights hit the lens.
By kitted you mean the cemented elements?

If that's all that's going to happen that's great! Contrast can be boosted in post but I was concerned about artifacts in the photo that I'm too lazy to photoshop out.

QuoteOriginally posted by Vasyl Quote
I would clean the haze up (if that is possible) to see the colors.
I would attempt to clean up the haze if I knew how to take apart this particular lens, I've taken apart 50mm's but the front element can be removed through the front and this lens doesn't seem to have a masking ring (whatever you call that where the info is inscribed) on it.

Thank you for your speedy replies.

03-13-2013, 02:00 PM   #5
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I'd send it back as "Significantly Not As Described".
03-13-2013, 04:55 PM   #6
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QuoteOriginally posted by johnyates Quote
I'd send it back as "Significantly Not As Described".
Me, too. There are lots of macros out there. Even if it was a little more expensive, I'd like one in good shape that is not growing things.
03-13-2013, 05:15 PM   #7
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QuoteOriginally posted by SpecialK Quote
Me, too. There are lots of macros out there. Even if it was a little more expensive, I'd like one in good shape that is not growing things.
If they were only a little more expensive I wouldn't care but all the ones I've seen that are buy now or actually mint condition go for over double what I paid and I am on one of those things some people use to manage their money, a budget. Also if it were growing a mold I'd have opened it from the back and swabbed a culture for my microbio class already.
03-14-2013, 07:25 AM   #8
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That lens is prone to separation/deterioration between the cemented elements, and that looks like an example. I took mine to a local repair shop and they felt it couldn't be fixed. It shouldn't infect other lenses, but might get slightly worse. Direct sun or a strong light source into the lens will drop contrast something fierce, but with a good hood you could probably get away with it in most uses. Unless it was REALLY cheap I would probably return it.

03-14-2013, 08:17 AM   #9
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QuoteOriginally posted by Nick Siebers Quote
That lens is prone to separation/deterioration between the cemented elements, and that looks like an example. I took mine to a local repair shop and they felt it couldn't be fixed. It shouldn't infect other lenses, but might get slightly worse. Direct sun or a strong light source into the lens will drop contrast something fierce, but with a good hood you could probably get away with it in most uses. Unless it was REALLY cheap I would probably return it.
Thanks for the info ... I was not aware of this potential problem ... I have a M 100/4 which is (still) clean, thankfully ... J
03-14-2013, 08:36 AM   #10
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QuoteOriginally posted by johnyates Quote
I'd send it back as "Significantly Not As Described".
+1, I'm afraid I would be returning it too.
03-14-2013, 08:43 AM   #11
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QuoteOriginally posted by Nick Siebers Quote
That lens is prone to separation/deterioration between the cemented elements, and that looks like an example. I took mine to a local repair shop and they felt it couldn't be fixed. It shouldn't infect other lenses, but might get slightly worse. Direct sun or a strong light source into the lens will drop contrast something fierce, but with a good hood you could probably get away with it in most uses. Unless it was REALLY cheap I would probably return it.
I think I'll use this knowledge to see if I can get a partial refund from the seller so I can keep it and not hunt around for another one for weeks. It was really cheap compared to what all of the other auctions went for in the last few weeks that I've been trying to win the lens so I think it's worth keeping. Also I don't shoot in bright sunlight a lot but I am going to experiment today with it to see how bad it really is and if I'm okay with the lower contrast.

Thanks for your reply.
03-14-2013, 09:18 AM   #12
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Hi Kricket, try to contact a lens repair to get approximate cost of repair and then speak with the seller - I think it would be fair if he covers the cost of repair. Otherwise return the lens.
03-14-2013, 04:46 PM   #13
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QuoteOriginally posted by vrrattko Quote
Hi Kricket, try to contact a lens repair to get approximate cost of repair and then speak with the seller - I think it would be fair if he covers the cost of repair. Otherwise return the lens.
They offered me 50% back, which makes the lens dirt cheap so I took that. I sent an email to precision camera to see if they can clean it but no word back yet. Even if it can't be fixed, it takes really nice shots outside of direct light which is about 90% of my work anyway. Anything in bright light would be a landscape and I'd use a different lens so I think this works for me.

Example of non bright light shot:



I'm totally okay with that.

Still want to know how to take off the front element if anyone has any ideas. If I have to take the whole thing apart then never mind though, I always lose pieces.
03-14-2013, 06:33 PM   #14
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Usually the front ring (with the writing on) can be screwed out using something round and rubbery. Maybe a jar opener pad on the top of a baby food jar, or something else that allows you to put pressure on the ring but not on the glass, Then you can see tiny screws that will free the front element. Or, maybe then the element rotates out, depending upon the design. But I will warn you, sometimes the problem is deeper than it looks form out side the lens, and before you know it you've got parts everywhere. Be very careful where you put screws, which way the glass goes, etc. if you decide to try.
03-14-2013, 10:48 PM - 1 Like   #15
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QuoteOriginally posted by Nick Siebers Quote
That lens is prone to separation/deterioration between the cemented elements, and that looks like an example. I took mine to a local repair shop and they felt it couldn't be fixed.
If you are really determined to repair the lens back to its former glory you could try this :

The SMC 100/4 is a pretty old lens Pentax would probably have used Canada balsam to cement them - you can separate the elements by softening the adhesive by heating at 150C, and after separating the elements cool them down (carefully) and soak the separated lens elements in acetone. This should remove the balm from the lens surfaces and then you can attempt re-cememting them with a modern UV curing optical cement*- be warned this does require some specialised equipment and skill also re-centering the lens elements after separating them can be very difficult.

Some more modern lenses use UV curing cements which have to be removed by soaking in acetone,or in a solution of 50% NAoH** (sodium hydroxide) I have used cryogenic methods (liquid nitrogen) to physically shatter optical adhesives between lenses - but I do not recommend this.

* UV curing cement is easier to use than Canada basalm - because it retains its low viscosity until it is exposed to concentrated ultraviolet light - so you have plenty of time to get the lens aligned perfectly. The materials I use to de-cement and re-cement lenses are available here
** Be careful when mixing up this solution, remember to add the NAoH to the water - not the other way around. When NAoH comes into contact with water a considerable amount of heat can be released which can be hazardous. Also be warned that NAoH is rather corrosive, so wear appropriate protective equipment. I have heard that 3M Safest Stripper Paint and Varnish remover can be used to remove optical cement but it takes considerably longer than concentrated solvents.

Last edited by Digitalis; 11-01-2013 at 09:17 AM.
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