#12
Post
by apochronaut » Mon Jan 13, 2020 12:06 pm
Since various cements have been used in compound optics, de-lamination has different characteristics, depending on the type of cement used. In some cases, the factory providing the cement, made a dud batch, which did not stand the test of time or the formula turned out to have a photo reaction over time. Most problems however , are caused by the drying out of volatile compounds in the cement. While there is no doubt that contraction of the glass elements and cement in complex optical systems can accelerate de-lamination, the de-lamination is usually caused by one of several other things. A) evaporation of volatile compounds in the cement or B) Improper curing of the cement or C) a photo reaction in the cement. D) mechanical shock or torsion. or a combination of .
A lot of de-lamination in optics, takes a circular or concentric form, showing first at the exterior of the optic and working inwards over time. Often, one can see that the cement has essentially dried out, from the outside of the cement layer in. Sometimes, crystals are formed due to the drying. This is very common with balsam . Sometimes, drying can be enhanced due to low temperature contraction and therefore increased exposure of the cement layer to air, or can be just enough that a severe temperature drop finishes the process, or can allow condensation to enter during the period of warm up. In large optics, condensation can get trapped.
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