Aratus wrote:Unless there is something new happening that I don't know about,
From what I've seen there's not much chance of that!
Don't you believe it. There are always new developments! It is hard to keep up with everything sometimes.
Some people when looking through an SCT are surprised to find that they don't
get a doughnut shaped image everytime they look through it! (and of course a Newtonian reflector has much the same problem. ) What actually happens is that normally the 'shadow' is dispersed across the image, and the only effect is that gives a slightly lower contrast. The 'doughnut' also turns up if the telescope is less than focused, and a long exposure of a faint area just gives a field of doughnuts! Specks of dust can also end up as 'dark doughnuts' on your images.