Posted 17 November 2013 - 10:56 AM
I have read numerous guides online that say that collimation is easy. It wasn't for me! Any advice?
Posted 20 November 2013 - 01:42 PM
Also, those FR's aren't made by Zeiss, you know.
Posted 22 November 2013 - 09:23 PM
For best results get your scope in critical collimation (I don't mean close; I mean dead on) before screwing on the reducer/corrector. My personal preference is not to collimate with the reducer/corrector installed.
There are additional threads here on CN dating back to 2010 and on a couple other forums and they all recommend collimating without a reducer installed.
Bottom line... Follow Larry.
Posted 22 November 2013 - 09:29 PM
Remember collimation, will change on an SCT (though it should not be by
much), as you adjust the focus, unless the baffle tube is absolutely
perfectly aligned (unlikely...). When you add a reducer, it is normal to
have to shift the focus by a significant amount. Hence it is quite common to
find that previously 'perfect' collimation, is no longer quite correct. This
is why for truly 'critical' collimation, it is best to align with the scope
in it's final optical configuration.
Second, if the collimated optical axis of the scope, does not pass through
the central axis of the reducer, collimation will again show problems.
It sounds as though your reducer has the second problem (since another
reducer doesn't display the same fault), but the comment 'different
F-ratio', does imply that the focus distance was probably changed between
the units, so the first possibility should not be ruled out. Also certain
types of fault will get worse as the focal ratio decreases (if for instance
the CCD is not perfectly perpendicular to it's mechanical mount, the edges
will show both coma, and misfocus, when using a reducer, and the amounts
will increase with the reducing ratio, perhaps being invisible without the
The probability is that the optics are not properly aligned in the body.
Hence 'assembly' (or even a significant knock, that has shifted the optics
to one side of their adjustment), could well be the problem. However it is
also worth being aware, that a scope which is perfectly collimated with a
diagonal, which is itself not perpendicular, will have the collimated
optical axis 'off centre' to the rear baffle tube. If a reducer is then
fitted at this point, this will be off-axis, and will show problems.
Generally, the F/6.3 units are normally pretty good, and it may well be that
Posted 25 November 2013 - 12:59 AM