Re: Mach2 - Imaging in frigid night


Roland Christen
 

The King rate is not based on a model. It is a calculated custom rate that is created inside the CP4/CP5 controller and is accessed thru a simple command, similar to what you would send to get Lunar or Solar rate. Although Sidereal, Lunar and Solar rates are fixed rates, the King rate is a variable rate. The rate is calculated inside the CP controller and depends on the position in the sky. The rate is accessed via a simple command sent to the mount from the keypad and I believe from APCC (although I don't know for sure). I don't remember the command right now but can get it from our tech guys on Monday.

The equation for the King rate works for most of the sky until you come close to the horizon, at which point it is limited. Here is a primer of what the King rate does:
https://canburytech.net/DriftAlign/DriftAlign_3.html

This one allows you to compare King and Sidereal rates for any point in the sky:
http://www.bbastrodesigns.com/equatTrackingRatesCalc.html

I do want to point out that this does not compensate for polar misalignment and Dec drift. Dec drift is normally a small fraction of RA drift, and it can be mostly nulled out by proper alignment of the azimuth axis. In the case where I was shooting down low in the east to image the Rosette early on, the RA drift rate was around 30 arc sec per hour, the Dec drift was only 5. If you're going to guide, it is nice to have the RA rate close to what is actually happening in the sky so that the guider is loafing along.

If you want to do unguided, then you can do a quick model of the path that the object will follow. 5 or 6 points will do nicely. In my case I'm taking 20 minute exposures at 1200mm focal length and I wanted to see how well the system guides at 1200mm on a bitter cold night, with about 70lb of scope and equipment attached.

Rolando



-----Original Message-----
From: Jim Fakatselis <pashasdad@...>
To: main@ap-gto.groups.io
Sent: Sat, Jan 23, 2021 2:31 pm
Subject: Re: [ap-gto] Mach2 - Imaging in frigid night

So there is no easy selection for King rate without a model?
Is this perhaps a possible opportunity to add it as an option button in APCC?

Jim


On Jan 23, 2021, at 12:10 PM, Roland Christen via groups.io <chris1011@...> wrote:


Yes, that is correct.

Roland



-----Original Message-----
From: Worsel via groups.io <bryancashion@...>
To: main@ap-gto.groups.io
Sent: Sat, Jan 23, 2021 10:41 am
Subject: Re: [ap-gto] Mach2 - Imaging in frigid night

Roland

Jim's question prompted a related thought.  I assume there is no need even to bother with King rate, if using an APPM model with MGBox for environmental conditions to correct for refraction.  Is this correct?


TIA

Bryan

--
Roland Christen
Astro-Physics

--
Roland Christen
Astro-Physics

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