terryf

I have a 294MC Pro and use a cheap flat panel that I bought from Amazon (other good retailers are, I’m sure, available), and I modified it using the method detailed here - https://www.blackwaterskies.co.uk/2020/03/cheap-diy-remote-controlled-flat-panel/ The modification itself is easy, all you need is a soldering iron, pretty much, and the only issue I remember having was getting the program right on the Nano (it was the protocol was the issue, not the programming as such). Now I can plug my panel in and set the brightness or (in NINA) I can let it find the brightness level for a 3 second exposure - flats are so easy now. I also have two sheets of opalescent Perspex with a couple of sheets of white paper between then to drop the brightness a little, though that is not needed for NB flats. Although the panel was cheap, I’ve tried it in various orientations on the scope and the flat does not change significantly, so the panel is producing reasonably uniform illumination.

I'm not sure that the FWHM matters all that much. The guiding routines work by figuring out the centroid of the star (or stars in multi-star guiding), and the view seems to be that precise focus is not necessary as a bit of defocus won't alter the calculation of the centroid. I've even seen it said that defocussing slightly is beneficial, and I can sort of see the logic to that. If all the light from a star was not dispersed in any way, its light would pure falling on one pixel (unlikely, but just go with me in this) and the centroid could only ever be at the centre of that pixel irrespective of where it was actually hitting it. However, if the light is smeared around a bit over multiple pixels, then the calculation can locate the centroid to sub-pixel accuracy as long as the smearing is done in a repeatable way. If that is true, then a high FWHM figure shouldn't be a problem I'd have thought. Where I live, seeing is the main limitation on guiding anyway so an APO wouldn't help me, but multi-star guiding seems to help significantly with that. As an example, I use a 30 mm SvBony guide scope (120 mm FL) and I manage to get sub-arc second guiding on my AZ-EQ5GT - mind you I don't actually know what FWHM that scope achieves. Terry