I bought a pair of binoculars and when I found that one of the objectives was partially de-cemented- Looked cloudy through about half of the lens, wondered if I could use mineral oil for a temporary interface between the doublet elements while I contemplate what I'm going to purchase to bond the 2 elements (likely Norland #60). I removed the objective from the lens cell and founds that the 2 elements were completely separated, so all I had to do was clean off the residual balsam (early 60's sunscope wide angle) with a bit of lacquer thinner/ acetone/ goof off to get them ready for bonding. I'm guessing outside of a thorough degreasing when the time comes to bond that the oil won't be a problem when the final bonding is implemented. Opinions? Regards, Pat
temporary use of mineral oil for cemented binocular doublet objective- caveats?
Posted 17 May 2019 - 08:29 PM
I did try them dry. It seemed to me a bit dimmer with a bit of veiling glare that wasn't present on the other side at low sun angle.
I don't intend to leave the oil on the lenses. Just for a week or so to see if the bins are worth spending the dollars on for the lens fix. The fly in the ointment is that the shelf life of the small size (1oz.) is 4-6 months for the uv adhesive. Regards, Pat
Posted 17 May 2019 - 10:03 PM
It was awful before oiling, with the lenses simply held again one another without any interface medium.
I used light motor oil or 3 in 1 oil, perhaps 20 years ago, who can recall. Great results.
The last time I used them 5 or so years ago they still gave indistinguishable images, side to side.
If i have to redo them (great binos, but the value is as family history), I will use a UV cured LOCA as an experiment, or use a proper optical gel or oil.
DavidG has a fantastic thread just this week on decementing balsam pairs, and how to properly recement then. Great like all his posts, search for it.
Posted 18 May 2019 - 12:06 AM
Photosensitive adhesive is the standard today.
Did you mark the original position before you take out the 2 lens?
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Posted 18 May 2019 - 03:36 AM
I did mark the orientation of the lens elements to themselves and to the lens cell as well as the cell wrt to the objective bell. Laid out a bit to check the full moon (or nearly so) image through the 2 sides and found the image no different from one side to the other- same number of false or ghost moons , same apparent brightness. I'm considering that a success till I get the proper adhesive. A question about balsam - since binocs are more often damaged from a fall more often than a telescope, does balsam typically fail that way? If I use a modern UV cured adhesive will that likely fail in the same fashion? There might be a reason to favor one bonding agent over the other if that is the case.
Thanks for the reference to the article in recementing in the classic telescope section made by DAVIDG. More knowledge is always much appreciated. Regards, Pat