A few weeks back, I did a test run with the LVI Smartguider. I mounted the LVI in the eyepiece holder of the 80mm refractor that I'm using a guide scope. This is mounted on my Vixen 8" reflector and the whole setup is driven by an EQ6 mount.
I attached my Canon 350D to the Vixen 8" (200mm) which was also using a focal reducer. The Vixen is normally an f/9 1800mm focal length telescope but with the reducer drops to an f/6.4 1280mm 'scope. The 80mm refractor is an f/6.4, 640mm focal length scope.
While initial impressions were good, when I finally got around to examining the images, stars were trailed as in this example (a section of a much larger image - skyglow is a real problem where I live):
The exposure was a couple of minutes long.
A second test also revealed trailed stars and the diffraction spikes on the main star shows that the telescope was a bit out of focus (click the image for a larger view):
The flaring around the star doesn't seem to be uniform so that made me think the 'scope might be out of collimation. But looking through the drawtube, I didn't see any indications of bad collimation. But this image of out of focus stars would seem to indicate that there is a collimation issue:
I suppose it's possible that the camera wasn't square to the telescope and that might have caused the stars to appear trailed and the telescope to be out of collimation.
Other possible causes are:
1. Flexure between the guide scope and the main scope (the way I've attached the two 'scopes may not be as rigid as I thought.
2. The EQ6 polar alignment might be out and need some tweaking.
3. Local wind conditions might have buffeted the 'scopes. The Vixen is an open-ended 'scope so it's good at catching cross-winds.
4. The Vixen, even with the focal reducer is twice the focal length of the guide scope, so that would magnify any minor tracking errors.
Rethinking My Approach
I decided the best thing to do would be to buy a dual-mount dovetail plate that would allow me to mount two telescopes side-by-side without them being in physical contact as with my current setup.
Then I figured it would be better to have two telescopes that were more closely matched, at least while I start out in astrophotography again. I considered the Sywatcher Equinox 80 refractor but, with the optional extras, was just a bit too expensive and I eventualy opted for a Skywatcher Evostar ED80. This is an 80mm, f7.5 refractor with a focal length of 600mm. The smaller magnification should be more forgiving of errors while I tune the astrophotography system.
If anyone can shed any light on the cause of the problems demonstrated by the above images, please leave a comment below.
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[tubepress mode="tag" tagValue="astrophotography"]
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