I have an AP 130 F/6 which I use for visual observations primarily of double stars although anything is game. I have read so many impressive things about CFF I have thought about getting one. What is your experience in terms of the need for increased aperture moving from a 130 refractor to see a difference? Is a move to 140 enough or would I really need to get a 160 to make a visible difference?
Here's a couple of answers.
1. Refractor to refractor, the jump from 102mm to 130mm, which is just a tad over an inch, is *very noticeable.* I think refractor owners are very much in agreement on this.
2. The other jump I've made, worth discussing, is from 8" to 9.25", when I sold the c8 for a 9.25. (Then I sold the 9.25 for a c14, and now I have a c8 again, plus the c14, but not the 9.25). The differences between a good 8" SCT such as are currently being made and a 9.25 are much more subtle than the differences between a 102mm refractor and a 130mm refractor. There definitely is a difference, but you have to pay attention. It doesn't hit you over the head (the jump from 9.25 to c14 hits you over the head). (I should clarify that I didn't sell the c8 till after I had a 9.25 and I actually side-by-sided them).
So, to conclude:
A one inch jump over the smaller 4 inch aperture is very noticeable.
A 1.25 inch (32mm) jump from a c8 to a c9.25 is noticeable but you need to pay attention. And when you have them side by side you can be struck by the fact that the c8 keeps up comparatively well. Indeed, I once tested the c8 vs. a c11, this was about fifteen years ago, on a series of NGC galaxies and out of 24 objects or so, the c8 brought in about 21. I wasn't making a particular effort to rank them by surface brightness or magntiude, just cruising next to a friend with a c11 and looking at what he looked at.
I don't think 10mm is enough over the 130mm to "make a difference." I think it will be even less noticeable than c8 vs. c9.25. So to the extent that you want specific targeted advice based on comparing aperture jumps, I think you're going to have to go for the 160mm for reasons stated. That 30mm is 1.2 inches and is going to deliver, proportionately to the five inch, more than the 1.25 inches does in the 9.25 vs c8, The 10mm is less than half an inch increment on a 130mm aperture which has already crossed a noticeable threshold from smaller scopes.
That 10mm helps the TEC compete against the TOA 130 and the AP GT and GTX 130. There's an edge particularly relative to money spent. But the 160 is going to be the scope that that gives the "oh yeah this is much better" reaction.
Edited by gnowellsct, 08 June 2017 - 09:53 PM.