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03-15-2013, 03:31 AM   #16
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I noticed the same haze in my 100mm macro and took it in for cleaning. There were no replacement elements available, and repair is just not justified. Pictures taken with it are still brilliantly sharp. I suggest you leave well enough alone.

03-15-2013, 04:47 AM   #17
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QuoteOriginally posted by Digitalis Quote
lens back to its former glory
That's fantastically detailed information, really first class.

I hope I never have to go down this route myself.

Last edited by Kerrowdown; 03-15-2013 at 06:33 AM.
03-15-2013, 08:31 AM   #18
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QuoteOriginally posted by Digitalis Quote
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
**I have also heard that 3M Safest Stripper Paint and Varnish remover can be used to remove optical cement but it takes considerably longer than concentrated solvents.
I'll keep my haze thank you very much. There are some dust particles I wouldn't mind getting inside however.

QuoteOriginally posted by Nick Siebers Quote
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.
This one doesn't appear to unscrew from the front. I have a 50mm A lens that I took apart for practice that does but using that technique doesn't remove that outer ring. Once I'm done using it (probably in a few months to a year) I'll play with it and see what happens.
03-15-2013, 09:46 AM   #19
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I've got one with the same loss of contrast in direct sunlight.
A hood helps a lot, but I don't really take many photos with this lens staring straight into the sun.
It was a good price, and it's a good lens.
I wouldn't get rid of mine and might even get around trying to get it sorted...one day.

03-15-2013, 11:11 AM   #20
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QuoteOriginally posted by Kricket Quote
...This one doesn't appear to unscrew from the front. I have a 50mm A lens that I took apart for practice that does but using that technique doesn't remove that outer ring. Once I'm done using it (probably in a few months to a year) I'll play with it and see what happens.
Macro lenses are often different because they need a longer focus throw. For example, I know the M50/4 does unscrew from the front, but some of the internals are the opposite of the M50/1.7. My second guess on Pentax lenses that don't unscrew from the front is to peel back the rubber grip and look for screws under it, or holes that will line up with screws at one spot in the focus ring rotation. That's how the lenses with slide-out hoods (e.g. M135/3.5) work.
10-30-2013, 02:03 PM   #21
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Hi,

I recently obtained a copy of the same lens with haze problem on Ebay. The seller had stated good condition, but receiving the lens I saw the haze which at the time I though this might be some light fungus or grease residue on the inside of the front lens. Pictures taken with this lens have a strong haze and are not sharp at all (compared to my nice M 100-2.8) even stopped down. I found this to be no acceptable condition.

Having cleaned other Pentax M lenses before without issues I thought this would be easy so I started to disassemble. This works easily as suggested earlier in this thread via the front. You can use rubber sheets as friction wrench or use two-sided adhesive tape together with some matching round object to press in and unscrew the front ring. After removing this you need a tool that fits into the small slots to unswcrew the retainer rings for the lenses/lens elements. I modified an old pair of compasses which works fine. After unmounting the front lens group I realized that the haze could not be cleaned as easily since it was between the cemented front lens pair :-(. I was tempted to send the lens back, but unfortunately I had made a pretty bad scratch in one of the metal tubes inside of the lens when slipping with the tool. I felt this was like "warranty void". After pondering a bit I decided to give recementing a try. At this moment the front lens doublet is soaking in xylol, hoping this ill dissolve whatever cement was used by Pentax on this lens in the original assembly. If solvent won't work I'll go to temperature method in the oven. My current status is shown in the picture.

For recementing I have decided to go for Canada balsam due to the ease of redoing it should the centering fail. Based on the research done I'm afraid it won't be possible to strip UV-curing epoxy should I screw up the first attempt.

I will let you guys know how it went.

Regards
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10-30-2013, 05:14 PM   #22
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QuoteOriginally posted by burnhard Quote
strip UV-curing epoxy should I screw up the first attempt
Acetone is a better choice for this purpose, IMO it is a better polymer solvent than Dimethylbenzene (Xylol) - but it can be tricky stuff to handle, it is highly flammable. And due to the fact that it is a known throat,nose,eye and lung irritant is best to work in an open ventilated area. The practical upshot of using Acentone is that it is UV - fluorescent : this characteristic makes it is easy to see if all the cement has been removed from the lens elements in the solvent bath.

Last edited by Digitalis; 11-01-2013 at 09:20 AM.
10-30-2013, 05:34 PM   #23
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QuoteOriginally posted by Digitalis Quote
I have used cryogenic methods (liquid nitrogen) to physically shatter optical adhesives between lenses
Wow.
You should make some YouTube videos of you at work. Would be very interesting.

10-30-2013, 05:54 PM   #24
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QuoteOriginally posted by rawr Quote
Wow. You should make some YouTube videos of you at work. Would be very interesting.
That would be the last thing I want to do. I don't want to be held accountable for destroyed lenses. People see stuff on Youtube and get the impression that anyone can do it - they can't. Liquid nitrogen is a hazardous substance to work with, if you handle it carelessly the results can be fatal.
11-01-2013, 05:12 AM   #25
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My m100/4 suffers from this as well. I'd love to have a go cleaning it up, sounds fun. Recementing sounds like the hard part imo.

The lens itself has a lack of contrast in brutal sunlight, but in the right light still produces some incredible contrast and detail. It's piqued my interest enough to get a proper macro lens, and since I wouldn't be able to sell it I'll definitely keep Digitalis info on hand, thanks!
12-05-2015, 05:15 PM   #26
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To burnhard

Did you have any luck with your adventure fixing the doublets in your ASAHI Pentax SMC 100mm 1:f4? Let me know. I had the same separation haze form in the small middle doublet, and am curious to your experience. I'll take yours for parts if you didn't succeed! ~Arne Kaiser
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