Any suggestions to re-balsam lens cells...? or I'm dreaming!

[c.d.ewen]

Read S. K. Grimes' methods (binocular prisms & v-blocks) here.

Charley

[Kevin Crisp]

The two pieces of glass appear to be physically centered, which is really good news.

I don't agree that boiling is the best way to separate balsam but this looks like UV cure cement so it doesn't matter what I think on that point.

1. Separate it with a soak in a solvent like MEK or acetone. Be aware of the fire/fume danger with both. Since you're half way there already, and it will wick its way into the gap by capillary action it won't take weeks, maybe a few days. As it works you will see the cement turning cloudy and you can follow its progress. When nearly all there you can probably slide them apart.

2. CLEAN the glass. And I mean clean. With acetone. Surfaces must be totally clean and lint free. A final wipe with acetone and cheesecloth works well.

3. Get a UV cure cement from Summers Optical. With an appropriate drop or two (it doesn't matter if it leaks out the sides, but if you come up short you have to clean and do it again) put the two back together on a very level surface. Pop any bubbles in the cement before you stick the glass together. Touching the bubble with the tip of the cement bottle has worked for me in popping them. Give the glue time to seep out to the edges. If you are almost there, you can smear the cement a little by sliding the elements around very slightly, but you risk air getting in there. Sometimes if you are almost there you can gentle push the elements together. There is a feel you develop for how much cement it will take for a certain size lens, and unfortunately you're doing your first one. You may end up cleaning them off and trying again if you come up short. There is a learning curve unless you get really lucky.

4. Physically center the glass using machinists' V-Blocks.

5. Using an UV bulb (the compact florescent black light bulbs work) give it a short exposure. Maybe 30 seconds or so. You are just trying to hold the two parts tacked together. You can use a loose drop of the glue on a microscope slide to see how long that takes. Remove the blocks, inspect the evenness of the glue and the centering.

6. If good, then give it a good 30 minutes or so with the UV bulb. Turn it over and give it some more.

7. Clean off the edges with a very light wipe with acetone.

8. Reinstall in the mount.

There are special solvents made for the post-balsam cements, but they are very flammable, have to be heated, and there is a risk of breakage and fire. Be patient and stick with MEK or acetone.

[Miguel Coquis]

A shot with this old tessar on 14x17" negative:"le Vide Plein"

[Miguel Coquis]

[QUOTE=Kevin Crisp;1279099]The two pieces of glass appear to be physically centered, which is really good news.

Thanks Kevin for the complete protocol you just post !
I believe it would be very useful not only for me.

[Tin Can]

Kevin,

Thanks for the concise and useful post.

[Steven Tribe]

I have listed why I think UV glue is not a good idea for DIY before.
In short: expensive, very short shelf life, need protection for hands and eyes, mistakes ( which may become apparent after curing) means labourious delays, requires safe uv source when the sun doesn't shine.

I don't know whether you have done any lenses with old balsam separation Kevin, but the process you describe is quite inadequate for these! There are always deposited residues around the edges which are not soluable in either acetone or water.

[Jac@stafford.net]

I don't agree that boiling is the best way to separate balsam but this looks like UV cure cement so it doesn't matter what I think on that point.

It separates before reaching the boiling point of water at ~sea level.

As for the fanatical cleaning of the edges, use 800-grit wet/dry paper. Fer crying out loud, stop down 1/2 stop. And for finesse, we ain't gonna live long enough to suffer the consequences of the small stuff and your grandchildren will care less than nothing.

[Kevin Crisp]

I've had the best luck with this cement:

https://www.optical-cement.com/cemen...l#anchor669157

I told Summers what I was working on and this was their suggestion. It does have a shelf life of a year, refrigerating it reportedly doesn't extend that, it does cost $36. They have cements with longer shelf life, but they require UV in the sunlight range so you're into getting a sun lamp instead of a cheap black light bulb. I think wearing gloves is smart and glasses too.

As to mistakes, yes getting the lens apart again if you fully cure it is time consuming. You might have to soak the elements for a week or two. It is much easier to separate them if you carefully inspect and find an issue, after just tacking them long enough as suggested. And if you have a bubble or incomplete coverage of the glue and you fully cure it, you've got your work cut out for you. I've got one protar where the cement did not quite fully get to the edge. Fixing it would have meant decementing the whole thing (4 lenses) and it works great as is and is stable so I've not redone it.

I have never tried using balsam to recement. I prefer not having to heat up the lens or cement.

[LabRat]

Big thumb's up to Kevin's post!!! That's what I have understood to do (but never got around to trying)...

A tip to tell what cement is holding it together; When held under a UV "blacklight" bulb, UV set cemented lenses have a VERY slight fog/glow look to them in the cemented area (even if they are assembled and you look into the front of the lens), where the balsam bonds do not glow...

Some light, even pressure is required while the cement sets... But difficult to apply correctly because the lens wants to slide around like a piece of polished ice on a convex mirror, and once pressure is applied for the first time, it cannot be released or bubbles can be drawn into the bond...

Using Canada Balsam for re-bonding is better, if the bond has to be re-done, VERY slowly heating/cooling it (to 140deg F), will release the bond so you can try again...

I would suggest sending it out for the service...

But I like the effect in the sample image!!! If the problem is bad and getting worse, send it out...

Steve K

[Kevin Crisp]

This person has an interesting method for separating balsam components, using a light bulb:

http://forum.mflenses.com/re-cementi...am-t34467.html

I know because I discussed it with Mr. Grimes that he heated the elements dry and then slid them apart. Sometimes they broke.

The only method I've tried is: putting the element on scrunched up aluminum foil in the kitchen oven. Tilt it. Set the oven to 100F. Go higher slowly in stages about 10 degrees at a time. There will be a sudden moment when the kitchen smells like a clear cut forest. Check the oven for when the top element starts sliding off the bottom. Take them out and quickly help the separation with a tooth pick or two. Put them back in the oven and turn off the oven and let them slowly cool. I haven't broken any yet.