New Forest Observatory ®

Now that the Hyperstar III is going to be the main imager for some time to come, I have just made some system hardware changes.  The (relatively) heavy Sky 90 has been removed as the guide scope and replaced with the old Celestron 80mm wide field refractor.  This refractor is extremely light and I needed to remove several counterweights from the C11 to achieve balance.  When I originally used this scope for guiding on the Hyperstar I, I routinely had an error graph showing less than 0.1 pixel excursions for the whole imaging session.  Using the Sky 90 as a guidescope I have never had such good guiding and typically errors would be around the 0.5 (or greater) pixel level during 3-4 hours of imaging.  We’ll have to see if this change produces sharper images from the Hyperstar III – I have the feeling we will see a marked improvement.

I now realise that the initial case I considered – a page of text facing a mirror with the page parallel to the mirror – was a very special, and very restrictive case – so it wasn’t really the best way to discuss “how a mirror works”. Continue reading →