Cheers Luiz
and Greg, the AG astrographs and I suspect all astrographs of this basic design, apart from heavy stiffening around the tube-focuser junction, definitely need OAG, particularly when using the big ProLine like cameras. I had differential flexure when I was using the ProLine meaning even exposures of just a few minutes showed diff flex. With the SX OAG now it is no longer a problem and I am now using exposures of 10min and could go longer but see no need. I always knew this (and could have improved my piggyback guide scope arrangement too!!!) but I just put up with it. Sometimes it takes a change to really realise just how bad it was
When I return to the using the Proline on the AG, or any other scope, I will be incorporating OAG in the train for sure.
Oh and remember, this image used no flats and no darks.
Mike