Did a Stowaway to C6 (Celestron 6" SCT) comparison tonight. Seems like a bad comparison in the sense of different types of scopes and very different costs, but in fact both are around 8 lbs and can fit under your airplane seat and run on a photo tripod, and so are candidates for a travel scope.
Only a 40 degree drop tonight and seeing wasn't bad. Bad light pollution plus the Moon. They were both cooled within an hour, but both were usable much earlier. The AP view did look prettier faster.
The AP star test was about the best star test I have seen. I find that at that very last instant before the ring becomes an Airy disk, something usually goes slightly asymmetric. Even if the Airy disk looks nice, just off focus, there is often a flaw there. For the Stowaway it was perfectly symmetric all the way to the Airy disk. And equal on the two sides of focus. The ring is slightly oval while the scope is cooling, but that goes away. (The oval stays oriented with gravity when you rotate the optical tube, so it is a tube current, not a pinched lens.)
The C6 had a typical commercial SCT star test for a good but not perfect specimen. The Airy disk was small but not quite symmetric. The intra and extra focus matched well though.
The AP view of M42 had perfect stars around it. The nebulosity was good. I could not see E or F with all the extra light around.
The C6 view of M42 had more bloated stars. More of the nebula showed. No E or F tonight.
The bright star below M42 has two faint neighbors. The C6 showed them better.
Both split Rigel easily.
Moon was great in both. About the same detail in my opinion, but I am not a frequent lunar observer.
I did not compare low-power views obviously because only the AP has them.
In daytime I looked at a distant sign. Neither could make out the words at first. After many minutes, the AP finally cracked it. Turns out the first letter was truncated at top, making the word unrecognizable, until you could see it well enough to decipher. Once it was figured out, the C6 could show it.
Also compared them on H-alpha with a Quark. I put an ERF on the front of the C6. The seeing was bad enough that neither was good. I could see the prominences but not the large but subtle filament or active region. I would need a better day. But the AP better match for the classic Quark with its 4.2x multiplier.
I was impressed with the 92mm AP for sometimes showing more than the 150mm C6. I was impressed with the C6 sometimes showing more than the 9x as expensive AP.
For travel, I often do want low power views, so that swings it to the AP. I guess if either I was afraid of losing the scope or if there was a particular dim DSO that I knew I would want to see, then I would bring the C6. Otherwise the AP.
EDIT: I will point out that the difference in nebulosity was much less than you would think from 92mm versus obstructed 150mm. I went back and forth to confirm the 150 showed a little more on M42. The high-quality optics with their contrast really did help the 92mm. But I need to compare them in a darker sky.
Edited by George9, 17 February 2019 - 07:06 AM.