This little beauty is a fantastic addition to SkySlab’s imaging train. Although it’s a pain to get it right in the first place.
A while back SkySlab acquired a CCD Tilt adjuster from OPT (http://www.optcorp.com/teleskop-service-m48-tilt-adjuster.html). It looks like this:The idea is that a lot of large-format CCD chips will not necessarily be 100% square to the projected image from your telescope. This often results in stars that are in-focus for 2/3 of the image, while the other 1/3 seems to be slightly (or in extreme cases greatly) out of focus. In an ideal imaging and optical system, every object would allow light to be refracted or reflected without changing the angle of the image plane. Not all things are ideal however and so we need to compensate from time to time. The imaging plane could be flat, or could be angled in many ways – for example:
How you compensate for an angle in the imaging plane is by:
- Compromising on your focus by moving it to a spot where all stars across the CCD seem semi-focused (near enough is good enough); or
- By aligning the CCD chip to be flat with the projected image so that you can achieve prime-focus across the whole field of view.
While that second option is the best option for astrophotography, it’s not easy to do. You add this to your imaging train, then you need to figure out in which direction the stars are un-focused in your image and remove the camera, correct the tilt, re-add the camera and test all over again.
Time invested was about two hours doing this on a clear night only to give up at the end and use the 1st option above instead. Still, persistence and determination are omnipotent so a second and third session was required to eventually get it right. Despite my frustrations, this is recommend this to all large CCD format astrophotographers. It’s well made, very accurate and well worth the investment.