I have a question about the two ways of focusing an R-C. One is with a fixed focusing plane and a movable secondary, the other is a fixed secondary and a movable focusing plane.
My impression is that the main advantage to the movable secondary is that heavy items such as cameras can be securely bolted to the back of the telescope so don't move, wobble, or shift. My impression is that the advantage to the fixed secondary is that of cost of manufacture, sparing the costs of mechanisms necessary to keep the secondary precisely aligned yet allow movement for focus.
Reading more, it seems that primary to secondary distance is very important and minor changes in the primary to secondary distance affects image quality.
Would a fixed secondary be a better design for imaging quality but at the expense of introducing "camera hanging on the end of a focuser" issues? Is the amount of change in distance between the primary and secondary enough to affect image quality? Are there other issues that should play a part in deciding between the two designs?
BK
My impression is that the main advantage to the movable secondary is that heavy items such as cameras can be securely bolted to the back of the telescope so don't move, wobble, or shift. My impression is that the advantage to the fixed secondary is that of cost of manufacture, sparing the costs of mechanisms necessary to keep the secondary precisely aligned yet allow movement for focus.
Reading more, it seems that primary to secondary distance is very important and minor changes in the primary to secondary distance affects image quality.
Would a fixed secondary be a better design for imaging quality but at the expense of introducing "camera hanging on the end of a focuser" issues? Is the amount of change in distance between the primary and secondary enough to affect image quality? Are there other issues that should play a part in deciding between the two designs?
BK
