I agree, Santiago. You can certainly test different magnification to see what's best. That's the strategy I employed observing Jove from 240x to 600x the other night. In doing so and in years past, I found something near 0.6mm to be best in the best seeing conditions available to us locally (usually Pickering 7/10 or better). It may be 0.4 or 0.8mm exit pupil on a given night. Or less, but rarely more magnification. I use 0.6mm exit pupil, which itself is an approximation, because I have no idea whether 0.55 or 0.62 is best. But, it'll often be somewhere in that ball park.
One reason I engage these conversations, other than sharing my experience, is the idea of "image breakdown". Folks may get the wrong impression about having a poor optic if Jupiter "breaks down" at higher magnification, but that is not always true. Some of the image break down is physiology and no fault of the scope, it's caused by the small exit pupil. I assert if your image is fine at 1mm exit pupil, at a sufficient magnification to really see a poor optic, then your image is fine at 0.5mm exit pupil, too. It's the same fine image we saw at lower magnification. If Jove is soft up at higher magnification, it's probably also too dim to see well. The problem is likely our own visual acuity at small exit pupils when our eye is operating at a very small relative aperture near 0.6mm f/35 or 0.5mm f/40. And that is perfectly normal for many folks.
As Miranda mentioned above, I see a great Jupiter at about 200x, give or take. But, while experimenting years ago, I noticed I was seeing a bit more at slightly higher magnification toward 0.6mm exit pupil where Jupiter is still just bright enough to register some color and some additional bright low contrast detail. Much above that and the image begins to dim affecting our own physiological acuity. For some, that may happen at 0.5mm or higher for an increasingly smaller number of sharp eye observers with above average acuity. I urge folks to try a bit more magnification and see, if not back down one notch and see, and so on.
But, the points are, if Jove is soft up that high, not to fret your scope necessarily being a poor sample. Also, you certainly get very sharp and apparently high contrast views at lower magnification, but you can gain something at a bit higher magnification. The eye likes both a bright and a large image, trick is to find that big bright image with magnification available to you. And it's often not going to be at 25x per inch rule of thumb, unless limited by seeing, rather at somewhat higher magnification if one is amiable to observing whatever seeing conditions prevail.
If Jupiter is a "fireball", that implies it's too bright and higher magnification (small exit pupil as the arbiter of image surface brightness) might be in order. Even in large apertures, Jupiter has right about the same surface brightness at the same exit pupil in all scopes large and small.
Edited by Asbytec, 05 July 2019 - 06:27 PM.