Quote:
Originally Posted by toyos
I have this image by Mark D. Russell, Ph.D published on Sky & Telescope years ago about the effects of central obstruction. There's an obvious difference in image quality between a scope with 0% obstruction to one with 18% obstruction. I saw similar results based on my own objective observations with various telescopes since I often bought telescopes just for the sake of comparing them myself (sold them again at a loss soon after). In my opinion, central obstruction is like your vehicle's aerodynamics, the lower the better (in most cases); there's no definite cutoff to it.
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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...
Actually, there is an easy test - make cut out circle of about 25% and adhere it to a bbq skewer. Get a mate to randomly hold it over/away (or just spinning it in situ will work) from your diagonal when you are looking at a subject and try to say when the aperture is in place.
Do this a statistically meaningful number of times and see if you were correct.
The theory is great, but reality is even better. Oh, and only try this in really steady seeing and on a dark night to get good data.