Quote:
Originally Posted by Astroman
Thanks Ray, I am not sure if I am getting this right or not so I snapped a quick image AFTER I had aligned the mirrors. Although the phone may show it slightly out, both sight tube and Cheshire say it's in line. So out of this image I can see the bottom of the focuser but it looks to be angled away, I would have thought the view would be looking directly up the Focuser tube, or is it.. I have moved the secondary back and forth along the tube and still get a similar image, some more some less... Anyway appreciate the thought on this image, except for the dirty optics  |
FWIW my interpretation would be that your secondary does not have an offset. Therefore, when you look directly down the tube like this, everything appears to be skewed off centre (but it is still optically collimated). If you look down the tube from the position where everything appears optically centered, you will find that the ota axis is a fair way from the optical one. If you back-project some light and put a layer of baking paper over the aperture, you can see how much of the OTA edges etc the beam is running into (which causes the strange diffraction pattern). You cannot get rid of this input beam offset unless you offset the secondary to compensate (or accept partial illumination of the secondary, which has its own problems). If you would like, I will bring down the offset secondary from my 200f4 to try before you decide if you want to modify yours.
regards Ray