Re: What eyepieces/filter for 10" dob

On Dec 7, 9:33 am, chambers...@xxxxxxxxxxx wrote:
I forgot to mention that I do have a 2x barlow. I've viewed planets
with the 10mm and 2X barlow. They move out of view pretty fast at
this level. I still have not mastered manually tracking them with the
Dobsonian.
Is any greater magnification useful?
I could get a 5mm and still use the barlow. I assume there is a
practcle limit with the 10" scope.

Try a few numbers that might be applicable to your 10-inch scope. Its
resolving power is, in theory, around 0.5 seconds of arc and that of
your eye is probably about 60 seconds of arc. Therefore if you use
60/0.5 or 120x you should be able to just detect the smallest detail
your scope can show. A "safety factor" of 2 would lead you to use a
mag in the range of 200-250x just to make the small detail easier to
see. Given that the seeing is often so bad that your scope can only
manage 1 arc sec or worse much of the time, this mag is probably OK.

However, the seeing does settle down momentarily from time to time.
If it improves from say 1.5 arc sec to less than an arc sec, you will
begin to approach your 10-inch scope's theoretical capabilities. In
this case having a 360x scope (3x safety factor) will likely prove
beneficial. If you are using 240x when this happens, you won't be
able to change eyepieces before the seeing turns back to mush!
.

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