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3 Days Ago - 2 Likes   #1
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Check you old lens carefully!

Today I was out for some pictures with me good old Pentax-M 1:4 100mm Macro.

Before I took a picture I found that the lens had very low contrast. I looks like fog.
All picture I took with this lens are garbagge!

At home I examine the lens carefully, oben it, clean the front lens, because I thought there was fungus
on the lens. But this was not the reason! The front lens depends on two lens glued together.
And the canada balsam between the lesen become bad!

View Picture EXIF
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It is not so easy to take a picture from this to show you.
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On the lens it is only visible with light in very special direction! It is easy for me to took a picture where you can not see it.

The last time I used this lens 6month ago it was okay. So it happen quickly when it happen. I don't think the lens becomes to hot. It did not stay in my car for example.

I check all my other lens and found another one. The old 200mm/4. With this lens it happens at the back side and it is
smaller, only at the border of the lens.

I search at ebay for the 100mm and found one with the same problem. So check the lens carefully!

I think I will now seperate the two lens, clean it and glue it again. Not an easy task of course!

Olaf

3 Days Ago   #2
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I'll check mine now.
2 Days Ago   #3
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Thanks for this info. Good to know.
2 Days Ago   #4
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That's unfortunate. I haven't found any good account of how this happens or what might prompt it. there are lenses which are known to be prone to this happening, the sigma apo 400mm f5.6 is a case in point.

Do let us know how you get on with any diy. There are some pointers here:

Asahi Pentax-M 50mm f1.4 Lens Haze with Balsam Separation Suspected, Repairing... - PentaxForums.com

Old Lenses can be restored by Re-cementing SKGrimes

Re-cementing doublet elements with Canadian balsam

https://www.optical-cement.com/cements/manual/manual.html


Last edited by marcusBMG; 2 Days Ago at 09:26 AM.
2 Days Ago   #5
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The 100mm macro seems especially prone to that as in I've seen it three times.
1 Day Ago   #6
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And mine has a spot that I first thougt was from a droplet drying on the front lens leaving a residual, but then understood was a beginning lens separation. This doesn't affect the IQ a lot, and can be fixed by an experienced repairman (Mighty Mike?). But it wouldn't be worth the cost, I've got a 100mm DFA macro that leaves the M lens in the dust anyway.

Kjell
1 Day Ago   #7
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I try now to find glue. Not so easy.
I think canada balsam is history for 50year. It is hard to believe that it was used by Pentax. Even the glue that was used after canada balsam is obsolete since 1980 because there was PCB inside.
Now it is common to use UV activated epoxy glue. I think I will try it. But the two lens has to be glued very exactly. I think better than 1/10mm because there is very less space in the mounting hole.

Olaf

---------- Post added 03-08-20 at 09:43 ----------

Oh, and my first thougt was to buy
the same lens at ebay.
But at the picture from ebay you can see that the lens had the same problem. So I agree, it looks that this problem happen no often to the old 100mm. What a pity! It is a nice lens.
1 Day Ago   #8
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Hello.
This is unfortunate, but alas a quite common issue on the Pentax 100 mm f/4 macro lens.
I have seen countless of them with the exact same issue sold "as is" on ebay.
This haze issue can also be present on other optical formulas of the same period.

It is a degradation of the cement inside a lens doublet.
By that time, I suspect the doublets in this lens generation were built using optical epoxy glue or UV-curing glue.
Canada balsam is a very viscous fluid, that remains pliable and does not fails like this.
If you look at the Takumar lenses, which are older : similar issues are quite rare.

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