Last night we had pretty decent sky, clear and cold. The transparency was excellent and the seeing condition was good. I took my 10" Dob out 3 hours to cool off and ran the fan. Then an hour before dark I took out my C102 f/1000mm 9.8. I like to look at Jupiter just after the sun sets before it gets to bright. Easily saw two bands and all 4 moons.
So now dark out, as good as it's going to be for a 1st. Qtr. moon I started out looking at some bright star clusters first before viewing the bright moon with both scopes. Then grabbed my nebula filter to gawk at M42 with the Dob and a 28mm SWA EP. I could see all 4 of the Trap stars and the nebula pretty much filled the FOV.
Ok, time for the moon and Jupiter. I had a 8-24mm zoom in the C102 with a Baader M&S filter and went for Jupiter first. Using a zoom to start out with gives me an idea how much power I can use to get clean views of the planet depending on the seeing conditions. I was getting nice sharp pin points of the moons in the lower end of the zoom's range from about 80-100x. I could see 3-4 bands in and out with 2 always there. So not great seeing, but maybe good at 3/5 I would estimate.
So now I'm over to the 10" Dob f/1250mm and I throw in my 13mmT6i for 96x. Jupiter's disc was ok, but I don't think the moons are that sharp? I next try my 8.8mm for 138x as usually that's ok when the seeing is just good. I check out the moon and see pretty good detail in the craters and mountains. I was not getting and wavy air that I usually see when the seeing is poor. I go back to Jupiter and try for best focus on the moons and when I get them sharp I just wait for the detail on the planet to come and go. I kept fiddling with the focuser and I just can't get those moons pin point. I go back over the the refractor to compare, yep the moons are sharp pin point there. I would describe the moons in the Dob as "bloated".
So I ask myself this simple question....why is my 4" $60 Achro outperforming the $500 10" Dob on Jupiter? The scope was cooled off enough I thought and the collimation looked good before I took it out, so I just don't get it. BTW, I use a Hotech laser for the collimation. It fits very snugly in the 2" focuser, so no slop there. If I get the center beam on the primary target when adjusting the secondary screws and then use the primary screws to center the laser dot on the laser bulls eye target, I should be good to go?
Anyway, this is not the first time this has happened to me, so I wonder if I am missing something or it's just the limitation of the scope, which is a Apetura model. BTW, the DSO's seem to be ok most of the time and 10 inches of light gathering shows it over the C102.
Thanks for any input...Bob