Re: Notified!😍 #mach2gto #Mach2GTO


Roland Christen
 

 
In looking at my graph without guiding input, the center of my RA trace drifted around 6.25 arc seconds in 11 minutes (in RA).    In DEC, the trace shows only  about 3.75 arc seconds of drift in 11 minutes.      The peak to peak of the each graph was similar, and more than 2.5 arc seconds P-P.     I sent this to you in a screen shot.   I expect this is telling me that the seeing was poor at best, based on these values.
The RA and Dec drift rates indicate fairly large Polar Alignment error. It means your Polemaster is giving you a significant PA error for whatever reason. That's why I don't rely on electronic devices for polar alignment. If you want the drift rate to be zero, then you have to do drift alignment where you twiddle with the Alt and Az adjusters until the drift rates are zero (which is the definition and goal of drift alignment). Ray Graylack's Pempro does that without muss or fuss in surprisingly short time. Once I have drift alignment zeroed in, I simply attach my right angle Polar scope, place Polaris at the correct point on the dial via the push-pull adjustment and I'm good to go from then on using only the Polar scope. Of course with guiding the drift doesn't matter, but for best performance it is good to have essentially zero drift. Yerkes observatory did it in the late 1800's and they had some pretty crude methods with that 40" refractor mount. But it was good enough to allow unguided imaging for considerable time exposures.
 
Every generation of astro-imagers has to go thru this learning process, and the fundamentals never change. The 2.5 arc sec P-P excursions are almost exactly what the seeing was for that night, so that will be the best you will get under those conditions. No way anything less than a $1million active guiding system along with high power laser for forming an artificial star will do any better.
 
By the way, your Vermont skies are not too bad. In the last week I had 1.2 arc sec FWHM resolution with no guiding (simple model in the keypad only) for 2 nights, then the seeing morphed into 7.5 arc sec FWHM stars when the trade winds picked up. Sky was crystal clear but stars looked like small shaggy dogs.
 
Rolando
 
 
-----Original Message-----
From: Terri Zittritsch <theresamarie11@...>
To: main <main@ap-gto.groups.io>
Sent: Mon, Mar 9, 2020 1:45 pm
Subject: Re: [ap-gto] Notified!😍 #mach2gto #mach2gto

On Sun, Mar 8, 2020 at 05:31 PM, uncarollo2 <chris1011@...> wrote:
1) Polemaster does not necessarily insure good polar alignment. Only drift alignment can reduce drift.
 
2) Having perfect polar alignment does not insure zero drift due to atmospheric refraction
 
3) doing a drift alignment can produce zero drift for both RA and Dec if you use the right method, but this zero drift will only occur in the area around the zenith. In other parts of the sky the stars do not move at sidereal rate, and will also drift slowly in Dec. This is fundamental, and no amount of polar alignment will prevent drift.
 
4) In our new keypad software we have added the King rate which reduces the RA drift in those parts of the sky where the sidereal rate is incorrect, however the King rate does not address Dec drift. We have modeling software in the new keypad which can be used to compensate for drift in both axes, and can allow unguided imaging. You can also go full model with APCC Pro, but I would recommend using that for permanent setups where you can spend some time getting a really good all-sky model.
 
Rolando 
 
Hi Rolando,
In looking at my graph without guiding input, the center of my RA trace drifted around 6.25 arc seconds in 11 minutes (in RA).    In DEC, the trace shows only  about 3.75 arc seconds of drift in 11 minutes.      The peak to peak of the each graph was similar, and more than 2.5 arc seconds P-P.     I sent this to you in a screen shot.   I expect this is telling me that the seeing was poor at best, based on these values.   I was still getting round stars (while actively guiding).   Such is life in Vermont under the jet stream!

I'm happy to report that I've successfully installed APCC, and set it up and at least tested it out without any clear sky.    Everything connects as it should.    Called George today, who was very helpful, to provided guidance on some of the finer points.    Now just waiting for clear skies.

Terri

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