Re: [Utah-astronomy] Meade LX200 - How to use with a DSI?
Daniel wrote:
When I say "generous" that may be an understatement. . . . . It also means that focus can be achieved at any distance behind the primary all the way to infinity, . . .
Thanks, so there is no theoretical limit. Chuck wrote:
The reason for a short-coupled camera is usually lack of swing-through room on a fork mount.
So the backfocus limit is a physical interference constraint. Thanks for the heads up on that one. I would not want to break a focuser tube off! Daniel wrote:
The drawback is the slow focal ratio which grows with the backfocus.
Although the light-weight easy-to-handle SCT package size is a big plus, one of the more confusing things to me about buying an SCT is their owners shell out for a scope with a 3000mm focal length and then immediately turn-around and spend another $200 for an adapter to turn it back into an 1100mm f/l Newt. I'll try to physically measure the backfocus and report back. Now if I can just find my ruler marked "infinitiy", "generous", "doesn't fit", "right-on", "adequate", "too small" and millimeters. -:) - Kurt _______________________________________________ Sent via CSolutions - http://www.csolutions.net
Do it during daylight, or using the moon focused on a piece of onion skin or tracing paper. Measure directly using a small ruler. A helper offering a third hand may prove beneficial. On 5/16/07, Kurt Fisher <fisherka@csolutions.net> wrote:
I'll try to physically measure the backfocus and report back.
Now if I can just find my ruler marked "infinitiy", "generous", "doesn't fit", "right-on", "adequate", "too small" and millimeters. -:)
One of the finest, most time-honored, critical non-traditional units of measure is abbreviated "R.C.H." Get me aside sometime and I'll let you know what that stands for. ;o)
The SCT was originally conceived as "everyman's telescope". It was designed to "do it all". And while it is very versatile, unfortunately it does nothing exceedingly well with the exception of travel. Even the Schmidt optical design is a manufacturing compromise. The corrector is ideally placed at the radius of curvature, not the focus, as every maker executes it. While this cuts the physical length of the tube in half, it also places some limits on imagery- and allows the manufacturers to sell corrective & augmentive optics as "accessories". Not to worry, the field is easily better-corrected than most fast Newtonians- just half the angular size for a given aperture. Insightful observation, Kurt. On 5/16/07, Kurt Fisher <fisherka@csolutions.net> wrote:
Although the light-weight easy-to-handle SCT package size is a big plus, one of the more confusing things to me about buying an SCT is their owners shell out for a scope with a 3000mm focal length and then immediately turn-around and spend another $200 for an adapter to turn it back into an 1100mm f/l Newt.
participants (2)
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Chuck Hards -
Kurt Fisher