Okay another session with the scope under the belt, under much better seeing conditions albeit worse transparency. The occasion was the de-consecration of OFLI's home observing field in Sonoma. The property is being sold, and this was our final session from the site. 12 years. Wow. Tempus fugit.
It was fun sharing the big Skywatcher with the others. Targets primarily were planets (Mars, Saturn and Jupiter), a couple of bright summer globulars, easy double stars and an opportunity to re-evaluate color correction and the star test (unfiltered this time) under better conditions.
The best news is that the optic appears to be centered with no evidence of wedge or similar errors. Star testing pretty much corroborated my earlier results under poorer seeing - an adequate but not fantastic optic. Better'n 1/4 wave but just at or even a little shy of 1/5 wave, and a bit over-corrected. Smooth enough but not super smooth.
I would put seeing last night around Pickering 7. For planets that were better placed above the slop (Jupiter early in the session and Saturn following) the scope did a credible job. In keeping with being a good but not great optic, usefulness in good seeing started to break down pretty early as magnification was ramped up. At 25x per inch (150x) a very slight deterioration of image sharpness entered the equation, though more detail was seen on both gas giants despite the slight softening. At 33x per inch (200x) things got pretty soft frankly to the point where the optic, not seeing, was doing more harm to the image than magnification was producing additional detail. As is typical Saturn remained a little "tighter" than Jupiter at this magnification level, but at 33x per inch I was definitely trading image quality for scale. While I'm not exactly disappointed, and my intended use of this instrument (more on this in a second) isn't affected by these results, this would not be my first choice in refractors for a planetary aficionado. IMO the ES 127ED is the better bet, having now used four samples of that scope and been generally impressed with planetary performance up to about 40x per inch in good seeing. But I digress.
My intended use of this scope is primarily deep sky, wide field observing, specifically in the context of guiding mounted binoculars to target regions using a GLP. It replaces a United Optics 6" f/5.9 achromat in this role. For this purpose it'll be a fun scope, with one qualification. The qualification being that the case is ridiculously huge (oversized). So much so that it makes it patently unpleasant to load, unload and transport the scope. Figure the scope in its case takes up 4x the cargo area in a vehicle as the 6" f/5.9 achromat in a padded lighting stand bag (soft case). I am noodling sourcing a padded carry bag for the OTA from Pacific Designs and reserving the metal case for storage.
I spent a good deal of time working on the focuser earlier in the day yesterday. I still cannot determine what exactly is making the irregular "clicking" as the draw tube is racked in and out. I did manage to reduce the amplitude of the irregularity by carefully paralellizing the roller with the draw tube flat and messing with tension "teeter-totter" screws, as well as four point tilt (the little rubber o-rings at each corner of the roller assembly attachment plate are pretty cool/clever. Next project is to use a sharpening stone to flatten the draw tube flat. I definitely need a replacement focuser, and would like a stock replacement, since even tuned carefully this one in current condition is a huge let down at any but minimal magnification.
Color correction. Hmm...a little better in better seeing unsurprisingly. But still plenty colorful on our old friend Vega. Definitely deep blue tinging violet CA on that star even at lower magnification. The issue of imperfect correction was made even more obvious by head to head comparison with a nearby FS-128. Ignorance is bliss. 200x on Vega is dispels any notion or pretension about this being an APO. On the other hand, flase color on Saturn was hard to find. But False color on Juiter was there albeit pretty subtle even at higher magnification. All by itself with no better reference would likely leave the owner happy with the amount of false color. Coming from a fast achromat, I'm tickled pink with the color correction compared to the achromat I replaced with this scope.
More to come...
Well if the image is breaking down at powers below 50x per inch i am sure i won't be happy with that. With my viewing tatse the scope would live at 60 to 80x per inch most of the time and be pushed to 100x per inch. 50x per inch is nothing for a super good 6" scope in my seeing. I know for a fact i would notice ho hum optics right off the bat. So if tnis scope can't give a true sharp image at 400 to 450x i would send it back in a flash as i live at power above 60x per inch for planets and the moon..
Maybe a better lens in the $4k price range would be a better hit for a 6" as i would not deal with a sub par optic at the 2K price range. I am hoping the one you got was below the normal that these scopes can do and maybe they vary from OTA to OTA. My AT102ED just keeps humming past 80x per inch and gives very sharp views. I have kept the AT 102ED for 8 months so that should tell everyone something.
Edited by CHASLX200, 12 August 2018 - 03:56 PM.