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Hi Glob3,
I must have missed that part. I havent read the article and when I click the link BTW it doesnt come up for some reason.
You are certainly right about the 5x being no good for the moon. Im just not that impressed with it at all for anything (other than 3 star aligning the Eq6) - so I may beg to differ on point 1 about the 5x being ok on other things. Maybe I just got unlucky with mine. My point is just that I hope the 2.5x GSO apo barlow is better than my 5x barlow.
My suggestion if you are not in a hurry is to try before you buy.
With a good refractor I've heard the max would be about 100x per inch (but probably less). Others can say 50x, but I've seen nice views through my 4 inch f10 achro at 275x certainly which is well more than that. I would look at your low power eyepiece and f ratios and work backwards from there. So from that if you were using a 5mm eyepiece with a theoretical max say of 320x (and probably a bit less than that) a 4x barlow would be more than heaps. You would get 200x with a 2.5 which sounds pretty reasonable.
Cheers,
David
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