widowmaker написа:А що не си представиш рефлектор с точност на стъкларията над 1/20λ,
обструкция на главното от диагонала 18-19% и апертура 12-14 инча?
Само две повърхнини, едната от които е плоска...
Малко данни за моя телескоп (Astroreflect 14" Gemini dobsonian):
Апертура:____ 355мм (352мм чиста)
Светлосила:__ F/5 (1750мм)
Разтоварване: 18 точки
Материал:____ BOROFLOAT®33 на SCHOTT
Диагонал:____ 66мм малка ос (65мм чиста), Antares optics, 1/30λ, Pyrex, R>96%@45°
Обструкция:__ 18.75% (по диаметъра) около 3.5% (като площ)
Фокус:_______ 10.5:1 микрометричен, нископрофилен крейфорд на Skywatcher
FOV:_________ 100% засветка - 15.27 мм, 75% засветка - 41.27мм
Sorry for the long quote Widowmaker, but I wanted to ask about if you had to pay any extra duty for the Antares secondary mirror, beyond 19% VAT.
I've talked with Sotis about upgraded mirrors for my 300 mm build that is already in progress, and he was concerned about paying added duty on USA made optics (beyond EU value added tax 19%).
We ended up paying a higher than usual specification Orion Optics secondary mirror with HiLux coating, but honestly the Antares mirror seems to still have higher specifications and as the British pound climbs in price I think in the future the target build for 12" and higher should aim for Antares -- except the total package price is higher. In my case I padded the price by 500 levas up front to allow for an improved secondary and HiLux 97-98% primary mirror coating, taking some chances on Orion Optics in UK. I think the next time I build a higher end telescope I'll go with Antares for the secondary mirror even if there are more cost after paying customs and taxes.
I also explored digital setting rings for Alt Az measurements and some sort of Goto later but decided it was enough to just build the best optics for now and add more things next summer when I might find money again. Already my savings from USA is almost gone! So glad to pick up a 300mm before Sotis gets famous and charges more money than any of us has If I do run away to USA next year I better have him build me a 8" to carry by airplane, and leave the better one here as a great reason to come back.
I'm getting a F = 4.5 focal length so I'll have to be careful about eyepieces. The Astro reflect low profile focuser does not support a coma corrector due to the coma correctors I've seen needing 60mm back focus. But Tsetsodrums manages to see with F 4.4 in his magnificent "Red Oktober", so I suppose the right eyepiece is everything. I remember he used some high end eyepieces to control coma, still looking for where he said this.
Still haven't mentioned to my wife; I pretty much hope to say "Hey I found a new job, it pays a real wage now, oh and you know, I decided to motivate myself for New Years with this portable telescope." I love to live dangerously, and that sounds like high risk
I had planned to buy a UPS for the astro society but nobody told me the requirements they wanted ;/