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The Bonding of Optical Elements: Techniques and Trouble Shooting. From Summers Optical

REMEDY: Cements can be modified with plasticizers or flexibilizers. Most manufacturers have available softer cements off the shelf. However, as has been mentioned they can exhibit higher outgassing figures. In the case of hemispherical doublets, the convex lens should have a slightly shorter radius to allow an equal space around the entire arc that will be filled with cement. A larger chamfer on the concave element to hold a larger quantity of cement to be drawn in during cure is of considerable benefit. Ring configurations should be designed with very tight tolerances so that although the percent of shrinkage may be the same, the mass is much smaller thereby reducing the overall change.