Quote:
Originally Posted by AstroJunk
That image is a simulation isn't it? The lack of rotation in Jupiter rather gives it away! I'd be interested to know how he got the 0% data - I can only assume he used refractors...
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You can measure 0% obstruction with a newtonian. make a cap for the end of it, with 4 circle cut outs. place it over the open aperture of the newt so that the spider vanes are situated between the circles, and the mirror is in the center... measure the area of the circles, do some math and figure out what the total unobstructed aperture of those 4 holes equals. If memory serves, you need a 16" newtonian to achieve 6" of unobstructed aperture... obviously its more weight/space efficient to have a 6" refractor, but it can be done...