Here's the photographic data:
400mm Telephoto f/5.6
Photo shot at f/5.6
Guiding ST-4 AE=3 @ 2000mm with SCT.
Is this a problem I could eliminate by stopping down the
lens 1 stop and exposing longer??
Thanks for the help!
Jim Ives
Hi Jim,
I have been known to overload an 8-inch SCT until it
cries real tears, but a 400 mm lens piggyback may be over the limit. My
take on your image is field rotation coupled with differential flexure.
The whole field seems to be rotating around a point in the upper right of the
image, but the hooked trails at the far reaches of the rotation arc tell me
the camera and lens were drooping relative to the guide scope. Stopping
down will not cure this. In fact, your basic focus looks just
fine. You just need more meat in the mount to held the camera rigid to
the scope and tweak the polar alignment.
