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06-04-2016, 06:36 AM   #1
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M-1.7 balsam separaion.

In my collection of 50s I have one M-1.7 that have what appeared to be ring of haze. It is very subtle but noticeable wide open, especially in high-contrast scenes. It is almost perfect at 2 and this is my sharpest and highest contrast 50 at 2.8.

When trying to clean it I have realized that problem coming from the inside of rear doublet. The rest of optics is pretty perfect.

I've never seeing and not able to find any info about balsam separation in Pentax-M. My copy obviosly has problem with whatever holding doublet together. I did find few references about "ring of haze" so this problem got to be common for Ms.

In attached photos you see this haze ring. Periphery is not hazy, this is not a shadow, but with close examination under the microscope I was able to see air (vacuum?) faults, just like big ones only really tiny. They shaped as fungus but they are definitely not, they appear rainbowy and only under very particular angle, so these are definitely separation of doublet, not fungus. Clear periphery around haze ring perfectly matches these little faults.

My explanation is that balsam or glue build stress over time. On periphery it gives ans suck the air in so it stays clear. Deeper it has no opportunity to develop fault and instead it shrinks and creates micro cavities, just like cavitation in water, that looks like haze.

I'm planning to attempt to rebuild this doublet. I hate to loose this copy as it is the sharpest 50 of my whole collection (@2.8). It resolves single pixel across whole frame on 20Mp APS-C.

Question: did anybody ever attempted to separate doublet on M-1.7? If so - what is the glue and what is the best ay to separate and clean it. If it is just Canada balm - I have plenty of ideas what to do.


Thanks Y'all!

06-04-2016, 06:50 AM   #2
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Here are the pictures:
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06-04-2016, 06:53 AM   #3
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You might ask @dcshooter for some info.
06-04-2016, 07:14 AM   #4
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QuoteOriginally posted by SalPro Quote
In my collection of 50s I have one M-1.7 that have what appeared to be ring of haze. It is very subtle but noticeable wide open, especially in high-contrast scenes. It is almost perfect at 2 and this is my sharpest and highest contrast 50 at 2.8.

When trying to clean it I have realized that problem coming from the inside of rear doublet. The rest of optics is pretty perfect.

I've never seeing and not able to find any info about balsam separation in Pentax-M. My copy obviosly has problem with whatever holding doublet together. I did find few references about "ring of haze" so this problem got to be common for Ms.

In attached photos you see this haze ring. Periphery is not hazy, this is not a shadow, but with close examination under the microscope I was able to see air (vacuum?) faults, just like big ones only really tiny. They shaped as fungus but they are definitely not, they appear rainbowy and only under very particular angle, so these are definitely separation of doublet, not fungus. Clear periphery around haze ring perfectly matches these little faults.

My explanation is that balsam or glue build stress over time. On periphery it gives ans suck the air in so it stays clear. Deeper it has no opportunity to develop fault and instead it shrinks and creates micro cavities, just like cavitation in water, that looks like haze.

I'm planning to attempt to rebuild this doublet. I hate to loose this copy as it is the sharpest 50 of my whole collection (@2.8). It resolves single pixel across whole frame on 20Mp APS-C.

Question: did anybody ever attempted to separate doublet on M-1.7? If so - what is the glue and what is the best ay to separate and clean it. If it is just Canada balm - I have plenty of ideas what to do.


Thanks Y'all!
Let's try again:

06-04-2016, 08:36 AM   #5
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dcshooter, Thanks for the advice. It is more of a challenge to me than practical thing, though I would love to have this lens back to full performance. I did pay ~$20 for this lens and as is it is very useable, pretty excellent, stepped down. My following questions: The best of my knowledge most solvents can damage most metals. Coatings usually metals or rare-earth. Is it safe to use Methylene Chloride or other solvent? Have you ever seeing any adverse effect on coatings after soaking glass in Methylene Chloride or other solvent? Is there any other way to separate this glue? Like heating? Other solvents? I'm planing to use LOCA glue for sell phone displays. It is cheap on eBay. Diffraction index is matched to that of a common glass, should be very comparable to Canada Balm or original stuff in this lens. Any thoughts on that? Thanks for your help!
06-04-2016, 03:42 PM   #6
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QuoteOriginally posted by dcshooter Quote
...I've heard of people using salad oil (1.47) with success when restoring older lenses, so it's possible you will get a way with it.
As a low-cost trial, you might try mineral oil. Several years ago I restored a separated doublet in a Pentax-M 40mm f2.8 using a VERY small droplet of pure mineral oil, and it's still working perfectly. I could tell no negative effect on performance.

-Joe-
06-04-2016, 05:46 PM - 2 Likes   #7
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QuoteOriginally posted by dcshooter Quote
Mineral Oil is also in the ballpark too at 1.48. The problem with oils is that you need to seal them in somehow. I've heard of balsam around the edges, but at that point, why not just use the balsam all the way through?
What you say is true - the oil might migrate. However, I had nothing to lose - worst-case I would have disassembled the lens, cleaned it up, and done something better. However, after several years it's still good. I really expected it to deteriorate before now, but I still use it and it works well. Now that I think about it, I remember cleaning the edges of the oiled doublet with some acetone to remove oil residue, then I applied a single layer of Scotch tape to hold it together and "seal" it, trimmed the tape flush with the edges of the glass, then blackened the tape with a permanent black marker. All free materials at hand. My Dad used to say, "There is nothing so permanent as a temporary solution." Ha!

-Joe-

Last edited by k0og; 06-05-2016 at 12:47 PM.
06-09-2016, 04:53 PM   #8
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Marinating...

I'm goofin'off this lens. After 48 hours I can see the rainbow propagating to the center of the eye. Cool! It is half radius there. Another 2-3 days maybe? I expect it to go slower as it gets deeper, closer to the center. Dcshooter, is goof off supposed to be that thick? I got one that says liquid, with spray bottle attached to the can. It is as thick as oil paint and looks like coconut water, cloudy clear with white chunks floating in it. Do I wait till rainbow reaches the center or should I try to help it by twisting it like avocado? Cheers!

06-15-2016, 07:22 PM   #9
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Next step.

dcshooter,

Just as you say, next day it separated on it's own. 3 days total.
Now I'm trying to clean leftover residue on flat surface of the doublet. Interesting that residue is only on convex. Concave is clean. First I tried my wife's nail polish remover. It says non-acetone formula. It got lens perfectly clean by eye, not counting that I still need to wash it more in alcohol because glicerin and some other oils in remover. So, it looks clean now, but, under microscope, only in reflected light I've noticed traces of peripheral voids. Only inner 20% of original fault ring has residue. Closed to the edge where voids where everything is clean. First I thought this is glass etching, but with sharp pin I can scrape it off and glass underneath appeared OK. So, it is not glass damage, it can be removed. Now I got purest acetone I can get but effect is the same - this residue is not solvable with either, alcohol or acetone. I assume MH can't do nothing more either.

In attached picture in red circle is the area that I scraped with needle (no scratches, I was very gentle). Clearly, this residue can be removed. Image is in reflected light. Nothing is visible in transparent mode.

It is not practical to scrape whole lens.

Do you have any idea what is it? How to clean it? Does it affect IQ? Should I just leave it?

(I'm still waiting for my LOCA order.)

Thanks
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07-01-2016, 06:28 AM - 2 Likes   #10
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Done!

My attempts to gently remove void marks seeing in my previous post where unsuccessful. I did marinate lens for another day in MH - no luck. This stuff is hard and I only able to scrape it off. Good news - it is transparent and my hope was that once it got wet with adhesive - it will get invisible.

Got my order of LOCA few days ago. Clean both half of doublet in acetone, drop of a glue, let it sit for a minute and glue them. Some orbital motion of one glass vs. the other got rid of small bubbles and I assume possibly even incident dust.
Inspected under microscope - appeared perfect.

I place it on granite block (left over from counter top) and push it from 3 sides with square aluminum blocks, leftover from machining project.

Day of curing under sun light got LOCA to thick jelly. At this point glass no longer trying to slip of its position. I got it and cleaned it with acetone. It appeared as new.
I placed it into UV EEPROM eraser for a few more hours.

Use 3 coats of black Sharpie on the edge.

Now, the deviation: in the lens this doublet set in the metal rim/bezel. Conical edge surface of convex side does not register reliably. I guess. possibly it is done to allow tilt adjustment of the lens. It would be a challenge to do it without special toot. But I've discovered that doublet registers reliably in the barrel and even without gluing to the rim, it fit snug. I just drop the doublet into rear barrel and screw its rim on.

The results:
Exceed my expectations. Lens is perfectly clear now. I cannot detect visually doublet transition. I guess index matching is good. Optical clarity of LOCA is excellent. Now, wide open I no longer have glow around bright objects. Stepped down it appeared just as sharp as before. I did not run strict tests on DOF planarity or distortion, but a few dozen shots do not appear to have any issue. Wide open it is a tad softer, as expected. Before I was never able to use it wide open as it had a glow.

My 5T no longer focusing on the glass. It picks up focus only behind glass. (I can focus manually, but, in this case, why?)

Total bill - <$10 for Good-Off and $1.50 for LOCA, shipped.

It was fun.

Thanks to Dcshooter for valuable advice.

Cheers Y'all!
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07-30-2016, 03:01 PM   #11
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Update... focal plane tilt.

It's being a while since I got this lens restored. One thing I've discovered: setting doubled by hand without special tool does have it's toll.

When checking sharpness (which did not suffer at all, well, when you find focal plane) and testing this lens with test charts and special patterns, I've realized that focal plane is tilted. Not a big deal at all. I've not noticed this in everyday use, only on test charts with focus assist moving around center axis it is possible to notice anything. I did test other Pentax 50 Ms and As. Most have tilt about 1 degree or less. This one has 2-3 degrees.

For any practical purpose this is nothing. But for purists this is something to be aware of.
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