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Hi Matt,
Earlier this year an acquaintance of mine in Brisbane asked me to look at a used Celestron C11 in Sydney for him and if it was any good to buy it. Everything looked fine and I purchased the scope for him and he subsequently picked it up on his next visit. In the mean time, as one would, I had a great time using it on as many occasions as the weather permitted. To keep my acquanitance informed a series of pictures of the scope and astrophotos were emailed to him. A couple of photos of the in and out focus of a bright star are shown here taken with my 350D through the C11. I can't recall which star or the magnification however they looked pretty good judging by published images of star tests. Needless to say the scope performs very well and he is very pleased with it.
Funny thing about star tests however is that they don't always give a true indication of a scope's performance. I have a number of Unitron refractors which show excellent pin point stars when focused however the star tests show quite different in and out of focus images and a fair bit of chromatic aberration as well as marked spiking on the outer fringes. Perhaps one ought not to look at stars in or out of focus but concentrate on the focused image.
Afterall most of us strive to achieve perfect focus, just look at the number of perfectly good crayford focusers discarded (mothballed) in favour of the more recent 10:1 varieties. While I'm waffling on, why is it that most of of us continually fiddle around with the focus/focusing/focus knob to achieve that "perfect" focus? Is there such a thing as perfect focus?
Cheers, Steve
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