I read different numbers for how much you can milk out of a specific
aperture. I am considering a 7" APO.

I own a few apos ranging from 3" to 8". I find that for low contrast detail ON
JUPITER that 30x per inch shows just about all an aperture has to show.

This is due to a combination of diffraction effects from the aperture, as well
as defects in the eye.

When it comes to double stars I am basically able to double this figure to get
the max resolution from an aperture due to stars being point sources, and not
as affected by either diffraction in the aperture or defects in the eye.

I think the Moon, being a higher contrast subject, lies somewhere between the
two vis a vis maximum magnification for maximum detail.

210x on Jupiter is enough magnification to proffer excellent images on Jupiter
given top notch optics. You see, the problem isn't so much how small the
details are as how poorly they stand out from their background (low contrast).

The more magnification you use, the more contrast is reduced.

So ideally you want to use the lowest power on Jupiter that will show the
detail in order to maintain the highest possible contrast.

Terence Dickinson in his "Back Yard Astronomer's Guide" recommends 25-35x per
inch for Jupiter.

I will be real happy if I am able to get max performance at 35x per inch this
year on Jupiter (using a binoviewer).

With my 6" APO I find that 180x (30 x per inch) shows just as much fine detail
as any other magnification ON JUPITER from my location and the views at that
magnification are quite satisfactory given good seeing.

A 7" APO at 210x in good seeing is not going to be something to sneeze at.

And then again you might be able to easily push it to 250x on Jupiter. I myself
will know more 9and be able to say more) about it in six months or so.

When it comes to Saturn, low contrast markings on the globe will be easier to
observe at lower powers. However, the rings are quite high in contrast so I
think it is easy to go well beyond the 30x per inch guidline to very good
effect when observing them.

I was alway impressed as to how good they looked in my 8" SCT. I finally
realized it was because they were of such high contrast. I could never get
quite the same effect using that scope to observe the fine detail on Jupiter
regardless of magnification.

My 2 cents,
rat
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