44 replies to this topic

[John Fitzgerald]

I bet that finderscope retainer ring is glued into the threads.  I've seen it before.

Edited by John Fitzgerald, 05 February 2021 - 05:40 PM.

[Jon Isaacs]

Decent calipers have hardened tips that can easily scratch glass. Having pointed tips with beveled edges makes it a bit scarier for me, too, as the tips can pop out easily. Screwdrivers are also deadly to lens due to sharp, hardened tips. Tempting though, resist.

 

 

I use calipers on a regular basis without causing damage.  I do on expensive eyepieces, refractor objectives. 

 

If the piece is a male thread, then the caliper is captured by the female thread and that prevents it from slipping inward. 

 

But If one is not comfortable with it, don't do it. It doesn't seem like a problem to me but I will say I am very experienced in the use of calipers.

 

Jon

[markb]

Interesting, Jon. Actual experience is always valuable information to have.

[Bob A (SD)]

After suffering through a miserably frigid month of below freezing and routinely below ZERO temperatures, my attention was returned to this finder lens issue.  

 

Repeated attempts with my old retiree's hands with their reduced strength from earlier decades were frustrating.  Again Martin to the rescue!  At first he too was unable to get the retaining ring to budge but perseverance paid off finally.

 

The doublet is currently soaking in acetone.   I've also cleaned up the threads on both the retainer ring and objective housing.  

 

But the question neither Martin nor I felt comfortable about was just how much mineral or 3-in-one oil to apply between the cleaned up elements.   One drop?  Three drops?  How much on a 50mm doublet lens?

 

[Bob A (SD)]

No one have a recommendation as to the amount of oil to use when reassembling the doublet elements?

 

 

Anyhow, here's a shot of the acetone soak progress after a day and a half.  Looks like this is going to take quite some time.

 

[markb]

It will sound trite, but enough drop(s) to fill the gap edge to edge.

 

My 30mm took one drop.I would guess it might take 2 or 3 for you.

 

The spread should be visible in the lens, especially if you use too little.

 

The curves are very similar so volume is very low. Similar enough that Newtons Rings should show in monochromatic (diffuse laser or, safer, green filter over a fluorescent with a green emission line).

 

Since you can try it out and re-oil for a final version, I'd be inclined to do a try-out.

 

Dust can be an issue, but a PecPad, available on Amazon can remove it.

[Bob A (SD)]

Thanks Mark.  Appreciated the sanity check.

[ngc7319_20]

No one have a recommendation as to the amount of oil to use when reassembling the doublet elements?

 

Anyhow, here's a shot of the acetone soak progress after a day and a half.  Looks like this is going to take quite some time.

My guess is between 1 and 3 drops of oil.

 

Careful not to scratch lens on bottom of metal bowl.  Perhaps put a paper towel under the lens?

[Bob A (SD)]

Well after two weeks of soaking, first with acetone which evaporated too quickly, and then with thinner, here's where I'm at.  Rather frustrated.  The two elements are still firmly together.

 

[D_talley]

You may want to try heat like I posted earlier in this thread.  I used 350 degrees and the two lenses came apart. 

[markb]

Read through DavidG's thread

https://www.cloudyni...norland cement

 

Heat is the best all around method from what I've read. Just gave to choose his to safely apply it.

Edited by markb, 14 March 2021 - 12:19 AM.

[ngc7319_20]

Well after two weeks of soaking, first with acetone which evaporated too quickly, and then with thinner, here's where I'm at.  Rather frustrated.  The two elements are still firmly together.

 

I dont think thinner will work.  Sorry acetone didn't do it. Might be time to try heat like others suggest.

[Bob A (SD)]

The doublet has been soaking now for weeks first for a few days in acetone which evaporated too quickly.  Then in paint thinner.  Looked like this which admittedly was discouraging.

 

SUCCESS

Decided to try one more thing before I heated up the oven.

I have a small inexpensive ultrasonic cleaner.  Warm water, a drop or two of Dawn.

 

The unit

 

And on the second 2 minute cycle...Separation!

 

Drying before cleaning

 

After cleaning

 

Taking a breather but will reassemble using 3-in-1 oil.  

Edited by Bob A (SD), 21 March 2021 - 02:44 PM.

[markb]

Wow, great idea.

 

I do wonder how much the presoak in acetone and paint thinner played a part, perhaps in partially opening the interlens space.

 

The action is usually stated to be through cavitation bubble formation and collapse, perhaps giving a micro hammering effect here. I use mine for cleaning watch parts.

 

This one is definitely on the 'try it' list. I have a 'snowflaked' 80 to seperate, and this might let me avoid the heating methods on irreplaceable 80 year old glass. If it fits my current ultrasonic pot.

 

And the heat mehods are always a fallback, so no risk longterm.

[markb]

Which gave more chemical separation, the acetone or paint thinner?

 

And what paint thinner (and base chemical) did you use?

[Bob A (SD)]

Which gave more chemical separation, the acetone or paint thinner?

 

And what paint thinner (and base chemical) did you use?

Mark,

 

  I think I've posted a few images of the soak progress.  The snowflakes all but disappeared with the outer 1/4" or more heavily clouded with the acetone soak (Klean-Strip 100% pure acetone).  Stuff evaporated 3 times on me eating up the better part of a pint which is why I moved to paint thinner.  Brand?  Sunnyside paint thinner 100% low odor mineral spirits.  Ended up with 100% of the lens cloudy, bubbly, and distorted as shown above with the doublet firmly cemented before I thoroughly rinsed it and tried the ultrasonic cleaner.

 

  I was happily surprised at how quickly the doublet separated in the ultrasonic cleaner as well as how much of the glue the Dawn seemed to dissolve away.  Used Zeiss lens cleaner on a microfiber cloth to remove the remaining glue.

 

  Oh and 3 drops of 3-in-1 oil did the trick reassembling the doublet.  

Edited by Bob A (SD), 21 March 2021 - 04:04 PM.

[markb]

Thanks Bob, exactly what I need to replicate your process!

 

It is good to have a possible no-heat, noncarcinogenic (but still requiring caution) solvent alternative.

[Bob A (SD)]

Thanks Bob, exactly what I need to replicate your process!

 

It is good to have a possible no-heat, noncarcinogenic (but still requiring caution) solvent alternative.

Let me know how it works for your 80mm binocular doublet.  

[markb]

It will be a while, 3 to 6 months but I will post or pm. 

[ngc7319_20]

 

  Oh and 3 drops of 3-in-1 oil did the trick reassembling the doublet.  

3-in-1 has acetone in it... helps dissolve old gunk on mechanisms... but may slowly evaporate over time...  haven't tried it myself

 

great job on doublet restore!  thanks for posting!