Thanks james, Peter,
I do suspect the secondary is not centred properly under the focuser. while using the cheshire, everything lined up correctly, but the reflection of the end of the focuser tube was not perfectly centred on the secondary. I didn't expect it to cause field rotation though.
James, would be great if I could try out the collimation of the OTA the way it is at the moment with the cats eye tools and see just how far it is. I could bring the ota across. will send you a PM.
how about the imaging scales of the ota and guide scope. with the 2.01 vs 2.68 arcsec/pixel relation, would it help if I used a focal reducer on the guidescope? will using a diagonal with the guidescope cause issues?
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