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That's cool. But I am wondering how they keep that big a piece of glass from sagging. I am asking because I have read that's a problem with big lenses, and a k
by woodandsteel 7y ago
That's cool. But I am wondering how they keep that big a piece of glass from sagging. I am asking because I have read that's a problem with big lenses, and a key reason reflectors became the way to go for large telescopes.
- mveety 7y agoTotal conjecture but it was probably factored in. From my standpoint if I knew it was going to sag, I would use that to my advantage if I could and, if not, at least factor it in.
- londons_explore 7y agoIf you factor it in, it means you can't reorientent the lens, since it relies on gravity to have the right shape.
- LordHeini 7y agoBecause glass does not sagg. It is a myth. https://en.wikipedia.org/wiki/Glass#Behavior_of_antique_glass https://en.wikipedia.org/wiki/Glass#Behavior_of_antique_glas...
- gattr 7y agoYou are mistaking two effects. Indeed, glass does not "flow" (it's not a "very, very viscous liquid"); but most assuredly it does sag under gravity - just as a heavy steel beam supported at the ends would. This problem is much simpler to solve for mirrors than lenses, as mirrors can be supported under their entire surface (see [0] for how it's done in larger amateur telescopes), while lenses - only along the edge. [0] https://www.cloudynights.com/topic/562906-18-point-flotation-mirror-cell-question/ https://www.cloudynights.com/topic/562906-18-point-flotation...
- randyrand 7y agospin it occasionally
- woodandsteel 7y agosee gattr reply above.