[ap-ug] [ap-gto] Imaging tonight with Mach2 at 5 below zero
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I use MaximDL for image capture and guiding. It's a simple program with no algorithms that you can set. Just MinMove and Aggressiveness. I use an off-axis guider with a Lodestar guide camera. My setting last night was 0.3 arc sec for MinMove and 6/10 for Aggress.
Last night we had almost perfect seeing (atmospheric stillness) along with very high transparency. Doesn't come along very often, especially in winter. Tracking and guiding below 0.2 is totally dependent on seeing (atmospheric stillness). Most nights I get perhaps .3 - .4 and my star resolution is around 2 arc sec FWHM. On the best nights when the atmosphere is really steady I can get 1.3 arc sec FWHM, but that is quite rare. So, depending on where you live and what your local sky conditions are, you may never achieve better than .3 rms.
You can judge the seeing quite accurately by just looking at the Dec trace, taking 1 sec unguided exposures for about a minute or two. Since the Dec axis is sitting perfectly still then the rms value is exactly the value of the atmospheric seeing. Of course you can't have any drift during that time which means that your polar alignment should be spot-on, but that is a given if you want close to perfect tracking.
This is what I got last night. I took a screenshot and unfortunately clipped the bottom off, but you can still see the rms guiding of 0.164 RA and 0.156 Dec. Guide scale is 0.95 arc sec per pixel. Guide exposures were 3 sec. at approx 4 sec intervals. As you can see there are many minutes of no corrections in Dec which attests to the almost perfect seeing. There are somewhat more RA corrections which I expect since that axis is tracking at all times. But overall the two axis errors are quite the same which results in round stars.
From: AaronW <aaron.wilhelm@...>
Sent: Fri, Jan 21, 2022 12:14 am
Subject: Re: [ap-ug] [ap-gto] Imaging tonight with Mach2 at 5 below zero
I am a new owner of a Mach2 and am extremely happy with it (my first ever mount, actually!). However, I never get anything close to 0.15 arc sec rms. I have not yet attempted to build a pointing model and am simply guiding with PHD2. But perhaps my PHD settings are not what they should be.
I am imaging exclusively in narrowband in Bortle 7/8 skies, and seeing conditions vary from night to night, but even under “above average” seeing conditions (as defined by the app “Astrospheric”), the best I can get is 0.3 arc sec total rms (think I was at 0.25 for a few hours one night).
I always image at a focal length of between 730 - 910mm, I polar align easily with SharpCap and am always within just a few arc seconds of error), and my PHD2 settings are as follows:
RA Agr: 70
DEC: Agr: 100
Scope: Mx RA: 2500
Mx DEC: 2500
Guiding exposures typically looping at 4 seconds and multi-star guiding is always enabled.
Any suggestions about how to optimize are welcome!
On Jan 20, 2022, at 8:14 PM, Roland Christen via groups.io <chris1011@...> wrote: