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I agree with Fred - some very useful comments Greg. The faster f ratio is significant. These CDKs and even corrected casses (eg Keller) have many benefits in bang for buck as well. The 12" RCs I built operate natively at f6.7 and also integrate a doublet flattener down behind the primary baffle tube. f6.7 or near is a plus for sure.
The faster RC ratio is at the expense of a very large secondary obstruction though - over 50% for me - so a negative there. I admit to being a plodder as far as getting images out there (maybe my motivations are different) so I will not comment on images etc. However, moving my own 12"RC and PME to dark skies is a real possibility. The CDK17 would obviously benefit from dark sky as said.
The sister 12"f6.7 RC is in dark skies south of Bathurst. At first setup, this RC gave amazing visual views in dark skies - using a 20mm and 31mm nagler eyepiece straight through - a real surprise visually actually.
guy
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