Big Bertha Needs A Better Atmosphere

I spent a bit of time with it last night, and this evening. (For once, we have clear skies.) I still think that the mirror is less than perfect (even with the turned-down edge masked off), but I think the limiting factor is now atmospheric turbulence more than anything else. I say that because for very brief periods of time, I can see a lot of detail in Jupiter's cloud bands at 222x.

Even at 400x on the Moon, the image is adequately sharp. (Not crisp like my 5" refractor or my 8" reflector, but not bad.) At least some of the problem is atmospheric turbulence, although if I go up to 500x, the Moon gets fuzzy in a repeatable way that suggests the problem is the mirror, not the atmosphere.

An interesting aspect of the problems with Jupiter above 222x is that Jupiter is a relatively low contrast target compared to the Moon, and Jupiter's bright features are so bright that they tend to wash out the darker cloud bands. I tried using a Moon filter (which takes away 87% of the light), and that seems to help. Various color filters seem to help--it might be worth finding 50% and 30% neutral filters, and see if the trick here to turn down the brightness.

One way of reducing brightness is more magnification (it spreads the available light out over a larger area), but then the intrinsic limitations of the mirror and atmospheric start to overwhelm whatever gain I get from reducing area brightness.

I need to do the following tasks:

1. Get Big Bertha to a low turbulence sky (where my new house is going).

2. Find a couple of neutral eyepiece filters less drastic than the Moon filter.

3. Accept the fact that because of the Dobsonian mount, I wouldn't be using above 400x on this beast very often, anyway.

4. Do a side-by-side test of Big Bertha and my 8" f/7 reflector. Optical theory says that a 17.5" reflector should show more than twice the detail at 200x of an 8" reflector, assuming that the two optical systems are of comparable quality. (Resolution is directly related to diameter of the primary.) My own impression is that this is the case--that Big Bertha is showing me more detail. But I do need to do a side-by-side to make sure of this.