Quote:
Originally Posted by Somnium
Hi John
thanks for the response, the real reason why i was keen to get an eyepiece on this is just to take advantage of the aperture and get some decent planetary views as well as a couple of DSO's. but from what you say it wont really be possible. it was very much an after thought, i got a telescope to put a camera on the back, not really for visual but it is nice to let people look through it when they come down and see my observatory. there is nothing that will connect you to space more than seeing Saturn through an eyepiece. but if it is better to do it through a 10 - 12" dob then i will do that.
just one thing you mentioned that was new to me was around the focusing of cassegrains. you say that all cassegrains achieve focus by manipulating the distance between the primary and the secondary, i understand that is the case for SCTs but with a CDK the primary and secondary are fixed. if extra travel is needed there is no manipulation of the primary to secondary distance, you just move the eyepiece further back. so how would this impact the optical performance or am i fundamentally missing something here?
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From what John was saying it sounds like the focus thing shouldn't effect your CDK as it isn't what would be considered a classical SCT. From memory the DK design works with two hyperbolic mirrors as opposed to having a parabolic primary on the SCT. The CDK also has a corrector (possibly in front of the secondary??).
As for how this translates to visual performance outside of the large secondary... I have no idea
