[Placidus (Mike and Trish)]

Originally Posted by atalas

Excellent M&Tth e creative juices are flowing.

Thanks muchly, Louie. There's plenty to get the imagination going in there.

Originally Posted by Lognic04

WOW!!!
I have to ask, how do you not blow out the stars with 1 hour subs?!!

Thanks, Logan.

Part of the trick is the 3nM H-alpha filter only lets through about 1% of the visible light.

Another is that the quantum wells on the 16803 chip are pretty deep. They can register 100,000 photo-electrons.

About 30 of the 8000 or so detectable stars in the image have indeed reached 65535 A/D counts in the exact centre, but each pixel has an anti-blooming gate that stops the full well affecting neighboring pixels. The outer reaches of these 30 or so stars that are burned out in the exact centre are still fine.

The long subs work well. We do enough subs to be able to statistically reject cosmic rays and satellite trails. In the dome, there is no problem with wind buffet up to about 40 KPH. We don't image if my hat won't stay on. We got the polar alignment spot on about 6 years ago and with our 2.5 tonne pier 1.8 metres into solid rock, we haven't had to touch it, so there's no problem with field rotation. As regards to tracking and guiding glitches, the FWHM is no worse after 1 hour than it is after 60 seconds.

We have very dark skies (except near the horizon), and for 3nM H-alpha, such long subs are justified. It is also just plain convenient to only have 6 or 8 subs to analyze.

Very best,
Mike