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Message: <blockquote data-quote="John Dracon" data-source="post: 3232573" data-attributes="member: 14799">Perhaps the only way to handle your concern is to do what you just said, put them in your centre console of your car and leave them there during the hottest  months.  My prediction is that the optical quality will remain unimpaired.  Of course you need to keep us informed, good or bad, what happens.  Just an observation.  The way the eyepieces focus in your Habicht is simple yet effective.  The threaded mechanism has a lubricant which fills the threads (male and female), and it may even have an O ring in addition. IF binoculars which I have had all operate this way.  Hence, there is minimum surface for the lubricant to act on. CF binoculars by design must have the oculars sliding back and forth with much more surface area lubricated, hence more capillary action which can occur, which is the only issue, IMO, that is relevant besides the deterioration of the rubber covering. Your Habicht has a metal alloy housing, and it and the lens and prisms will take more heat than will ever be generated in your car.  They may be hot to your touch and eyebrows and that is al, IMO.I think our resident expert, Bill the Navy guy, can speak with more authority on this subject.</blockquote>