Pinched Secondaries

[Astroman (Andrew Wall)]

Okay there is alot of talk on pinched secondaries of late and I am interested in finding out how you can test to see if your scope has some form of pinching.

In images of Stars or Planets with bright moons, when focusing on them they produce a coma like image before going into a not quite pin point. Some of this may be caused by the EP's, but I think there may be something else.

Below is an image of my secondary mirror in it's cell, this was before it was alumanised and the cell repainted.

http://www.theastroweb.com/astronomy...wscope_sec.jpg

Also the secondary was a little hard to put back into the cell for some reason.

[RAJAH235]

Hi Andrew, Your 2ndary shouldn't be 'tight' in the holder. I suggest you expand the brass fitting in some way or remove most of the overlap at the top, so that the mirror just 'sits' in & use a small dob of silicone on the back, before adjusting the clips. This should eliminate any 'pinching' effects.
PTN, my Meade 2ndary is simply glued to the back plate. No clips!
HTH. L.