Thanks Guys, appreciate your comments.
Quote:
Originally Posted by gregbradley
There's a point and you decide when it has arrived, when you ship the scope back at their expense and say please fix or replace. To have a solid case for that you will need to have done a thorough and reasonable set of tests to show its not user error but manufacturing error and that the error is not able to detected out in the field.
I think you are close to this point if not already there.
As you say obviously something is moving. Did you try to replicate the elongation by putting some light pressure on the focuser? I don't recall having any movement in my focuser.
Greg.
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Greg, i didnt put pressure on the focuser but i did loosen off the bearing block and nothing changed in terms of star elongation, it was elongated tight and the same elongation loose, although the image just shifted sideways. I would agree with Eric's comments bellow about the focuser.
Your scope has a bigger focuser than mime although its the same design.
Quote:
Originally Posted by ericwbenson
Hi Josh,
I really don't think it has anything to do with the focuser or image train behind the focuser. A tilted focal plane can only cause defocus by itself. If other aberrations such astig are present they can be more easily observed under defocus, however a tilted image plane will have an axis in focus somewhere and in front of and behind focus elsewhere. You will not see the same aberration pattern across the entire image.
If the scope can deliver good images near zenith then the optics are probably ok, that is good news. As you slew lower in altitude things go pear shape literally, star dispersion increases making then look like little rainbows (try it with a OSC camera), the dispersion axis vertically aligned, this is really obvious at altitude below 30ish degrees. What becomes difficult to judge is the relative contribution of dispersion compared with OTA misalignment, and how much you're willing to put up with. High resolution imaging can't be done below 30 deg altitude, so maybe that's a bad place to be testing things. But the image should hold up well between 30 and 45deg
Best,
EB
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Eric and Peter,
All my test images have been around the 30 - 40 degrees altitude range, and all of them have been with a red filter to minimize the chromatic dispersion, is this sufficient?? I was told to do my tests with a red filter by PW. I could try with my 5nm Ha though.
thanks
Josh