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Hi Amy, The magnification achieved with a given eyepiece is the focal length of the scope divided by the focal length of the eyepiece. Hence
750mm divided by 10mm = 75x mag. The max. mag for a given size scope is 50x per inch of aperture, so your 6"[150mm] scope would have a max of 300x mag. Sadly, these figures only really apply when the
atmosphere is unusually steady, maybe 3 or 4 times a year, depending
upon where you live. Most higher power viewing is done nearer to
30-35x mag. This would equate to about 180-210x mag. for your scope.
As mag. increases, so image quality decreases, so it can be a mistake to
buy an eyepiece giving too high a mag. A 4mm would be a good high
power choice.[187x mag.]. A 25mm would be a good low power choice.
There are two common eyepiece sizes, 1.25" diameter, and 2" diam.
Almost all modern scopes accept the former, and many have adaptors
so they can use either size. Your 10mm will almost certainly be a 1.25"
Even at 75x you should have seen two dark bands on Jupiter,
assuming that your focus was spot on.
raymo
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