Optical Quality and Effects of Secondary

Hi Martin,
Thermals in a SCT are a killer, the bigger the scope the worse it gets, I often found that with my own 12" SCT that it could take 3 hours or more to settle down, the central baffle that the primary mirror rides on is a big culprit for this. The plum off it would absolutely ruin the images and make the optics look like theyre uncollimated.
what is the newt you refer to with the 1/10 wave optics?
My own dobs mirror is about ~1/8th wave, but again, if the mirror is a few degree above ambient it mushes the planetary views, I have a digital thermometer on the back of it and a cooling fan, , just need to be carefull I dont cool it to the dew point, that can be an issue,

It's an ooptics f6 newt. Had it for many years, been thrilled with it for most of that! When I lived in rabat I used to leave it under the air con, or when not not too hot just let the evening breeze blow through it. Either option gave great views for whole observing session. I'm considering buying an sct cooler, it protrudes in through the baffle and blows Ambient air around, with exhaust vents at the back. Ivediy'd one with limited success.

Yea, a number of years ago I was going to get one aswell, dont need it now as its in an observatory these days so its always ambient.

Damian Peach has an interesting discussion on this topic on his DVD. Basically, as I understand his view on this matter, atmospheric turbulence has a far greater impact on image quality than optical quality and central obstruction.