Quote:
Originally Posted by multiweb
I think you'll need more than a 2x barlow on a 6".
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6" Dob is typically 1200mm f.l. (f8). Therefore 10mm eyepieces gives 120x mag. 2x Barlow gives 240x with 10mm eyepiece and this is more than enough on most nights and very good seeing is required. Exit pupil for 10mm is 1.25mm and for 2x Barlowed 10mm is 0.625mm with an f8 system. Exit pupil of 0.5mm is about the limit but requires exceptional seeing. This equates to a 4mm eyepiece or 8mm with 2x Barlow with your telescope.
The image should be twice as big with the 2x Barlow as without on any eyepiece.