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I image with 8” f5 and 10” f5 Newts with 60mm guide scopes ( not OAG ) and my image scale ratios are 4.2:1 and 4.0:1 respectively
By the way my OTA’s are carbon fibre which have minimal flexure and COE
Guiding performance is fine with both rigs
7:1 seems a tad high IMO depending on your rig’s mechanical set up , your mounts performance and local seeing
From my experiences aim for 5:1 or better ( if possible) Some folk have guided successfully with image scale ratios of 10:1 but I wouldn’t subscribe to that scenario
Cheers
Martin
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