[Daveskywill (David)]

See, if your outer stars look like (field rotation, direction) then you are too
far away and out of Back focus and if you have radial trailing-look like Star Trek
going 'warp' then you are too close to primary mirror (or to inside of Back-focus)

So this applies to RASA scopes and as you can tell it could get confused as
field rotation the first thing or 'coma' the 2nd one...you know.

To an untrained person or even un-orthagonality. but I found that even when
I was mostly polar aligned and had autoguiding going both axes that there was
a 'field rotation-effect' sometimes with my RASA back in Michigan so now I know that I probably was too outside of Back focus. So back then I only
sometimes probably heard about this but didn't think too much about it.

Now I need to.

So I'll use a visual method examining the stars around the outer parameter.
and stop and lock it (though I'd like to try using a smaller camera for this rasa too not just the qhy600) but a qhy178 but the 178 has shorter back focus. So I might just piggyback my scopes and hopefully have both orthagonal trained and collimated all scopes...want to eventually piggyback 3 other scopes besides the rasa 11".
jpg was taken from a youtube movie about the RASA and Back focus.

Hope this helps.