Quote:
Originally Posted by Astroman
Thanks for the input Steve, I had thought of this before. With my current tools, no laser or anything, it seemed ok to me. I used a steel ruler along the inside of the focuser and measured the distance from the front of the OTA. all seemed pretty right to me, but I know there are better ways to work it out but thats the best I could do.
I am interested to know why others with the BT-200 8" f/4 scopes have not reported a similar problem. Even if they all look okay, are they really and I am sure many wouldn't be perfectly collimated so would show some form of problem.
Going by what Ray has mentioned, it does look like the Secondary is not offset, I used the method of shining a light down the focuser (had to make an adapter for the LED torch to sit neatly into the focuser tube) onto the secondary and bounding it off the primary onto a piece of grease proof paper, taped to the front of the OTA... the result is below.
|
yep, looks like that is the problem - no offset and your input light is glancing by one side of the OTA edge, producing a lopsided diffraction pattern.
You can't get the light column centered without putting in a secondary offset.