in my experience it hard to beat an APO up to 5" with a newton that size.
Comparing my 113/900 (Vixen GP-R114E) with 0,885 Strehl has much less contrast on Jupiter than a Vixen FL102S APO. So visually I see more details and better colours. If the seeing is not good I see gray bands on Jupiter in the 113/900 newton and in the APO I already see brown bands at the same time.
Taking videos and making photos by stacking, sharpening ... Playing with the camera and with the software I can let the contrast rise and show things that were visually below the contrast border for my eyes so I can compensate the lack of contrast.
I have a 6" f/8 newton with 31 mm secondary. The mirror has 0,95 Strehl which is pretty good in my eyes. I bought it to avoid buying a 5" APO. I think from the contrast it's in the range of a 120 mm or 5" APO. What I somehow dislike is that it takes long time to be on surrounding temperature. During that time my Vixen 80L shows much better pictures. OK to avoid that I bringt the Newton 1,5 or 2 hours out before I start watching. Every time I had my 102/920 Vixen APO and the 6" f/8 Newon out I saw the same details in the APO and in the newton. The festoons and the Jupiter moons looked better in the APO and one small band showed a little bit more contrast in the newton. The viewing esthetics was always better in the APO.
For the Jupiter moons I often saw a ring like a diffraction ring around them in the newton and in the APO I don't. Jupiter show four beams coming from the spider that holds the secondary in the newton. OK I could use a curved spider but then the spider arms need to be thicker with more obstruction and some told me that the near area around bright objects get's brighter too. Up to now the larger 6" haven't visually showed me more than my 4" APO so for visually watching Jupiter I prefer the smaller APO as the esthetics of viewing is nicer. For taking planet videos the 6" newton shows it's real power. The beams, spikes are not visible but you can see the larger resolution there. Probably with better seeing conditions the 6" would show more than the smaller APO but to bring it up to a good 6" APO view I cannot believe.
For me that isn't important. I like watching with both my refractors and my newtons
If you want to have an APO > 5" or 6" you pay too much in my eyes. In this case I would prefer a reflecting system with maybe 1 " or 2" larger. For home use a 8" APO would be too heavy and much too expensive but a 10" newton is normally no problem.
So I needn't have an 6" newton that shows 6" APO views but of course it's interesting what you did to tune your newtons to get the most performance out of your newton to watch planets?
Edited by Niklo, 30 April 2015 - 04:17 AM.