I come from a heavy photography background -- 30 plus years, with camera gear in tow to all parts of the world, including really harsh environments (African deserts, summits of many mountains, including 24,000+ foot mountains, -40f tundras, etc.). I've used all sorts of lenses, and one thing about modern high-end lenses is the quality and durability of the optical coatings used in those lenses. In particular, the external elements of modern photographic lenses are extremely durable due to modern coatings, and flawlessly hold up to multiple and frequent cleanings.
In the last year or two, I've rekindled my love for astronomy (largely driven by my young son who has really shown a passion for it). My first scope when I was 10 was a 4" Meade SCT. Crappy scope because if I looked at it wrong the collimation would go out. Always a frustration.
Anyway, we're using a 4.5" APO at the moment, and I'm shopping for a larger APO. I'm not opposed to buying used, and have had discussions with sellers of 6-7" APOs from fine manufacturers (TEC, TAK, APM, etc.), and many of them are keen to tell me that "I've never cleaned the front element!" I had one guy send me a pic of the front element of a TOA 130 and it looked like someone ate mac-n-cheese off of it because it was so filthy.
But why? Are the coatings on good, modern refractors so soft and delicate that a gentle cleaning will wound the scope forever? Are the front element coatings that much less durable than the front elements on the good, modern photograhpic lenses from Canon, Nikon or Sony?
Or are astro refractor people just paranoid?
Asking honestly, because I just don't know if the coatings on front elements of high-end refractors are completely different from photographic lenses. And, to be clear, I'm mostly interested in the offerings from the better refractor builders -- as I said above, TEC, Tak, APM, CFF, SV, etc.
Coatings. Hummm. Thoughts?
Edited by GregInDE, 27 February 2020 - 09:21 PM.