I got a friend who just recently purchased an 8" SCT (took 8 months to get one because of low availability) and this morning he came over to test it for the first time and image Jupiter and Saturn. So, after aligning, as I was focusing on Jupiter I noticed a strange pattern on it's moons. Instead of the usual out of focus donut pattern, I saw what it looked like an "ON/OFF" symbol, basically a circle with a vertical line on the upper part. Did a test stack on Saturn and the image showed double limbs all over the planet.
I'm thinking the secondary mirror has a crack since nothing else looks damaged and there wasn't anything strange on the imaging train. We switched to my 6"SCT and we didn't have any issues at all, perfect donut pattern, no double limbs, achieved good focus.
Does anybody have an idea of what is going on with the optics?