You can look at the Conrady chart here. It is frequently posted on CN:
https://www.cloudyni...erration-chart/
As you will see, your 70mm f/10 is well "into the green." That's where you want your refractor to be. This is why your little refractor is f/10! If your 70mm were f/7 the color correction would be more similar to your 90mm, and the overall performance greatly reduced.
Your 90mm is not in the red colored junk zone, but it certainly is well into the "this really isn't very good" zone.
The focuser quality has nothing to do with it. The intrinsic (lack of) quality of the optics guarantees that the 90mm will be at a disadvantage.
On the good side you are learning why people who like refractors pay mega bucks for apos (and get fantastic focusers into the bargain).
Greg N
Last night I lined-up the Meade Infinity 70mm (f10) refractor, one of my ST80s, and the Celestron 90mm (f7) refractor. I let them sit for over an hour. I used the same eyepieces (sets of Kellners, Plossls, Goldlines) on all three (I had to use a barlow in the ST80 for the highest magnification).
I used Mars again for the test. I was just looking for a sharp image (not surface detail in these small scopes).
The Meade had the sharpest image by far and the Celestron 90mm the worst. The image in the ST80 was pretty decent. For highest magnification I used 140x in the Meade, 133x in the ST80, and 132x in the Celestron.
Even though the Meade had the sharpest image, I was surprised how well the ST80 performed at 133x. The image was somewhat soft, but it was still useable/serviceable. If all I had was the ST80, the image at 133x was still worthwhile and better that naked eye and binoculars.
I own two Orion ST80s (an early one and a late model) and a Gskyer 80/400. I had heard that the Gskyers are not as good as the Orion ST80s.
Last night, I compared those also. I could not see a difference between the Gskyer and Orions. If there is a difference, it is slight (to my old eyes).
I paid about $75 for the whole Gskyer kit used (like new). The tripod mount with the Gskyer performed better than my ES Twighlight Nano Mount. The Nano was a little shaky by comparison. But, they all work well enough.
Edited by Pluto 134340, 03 February 2025 - 07:05 PM.