Re: #Mach2GTO #APCC #Absolute_Encoders #APCC #Absolute_Encoders #Mach2GTO

Ray Gralak

Hi John,

Home is a physically fixed position. However, the park positions can vary slightly because they are relative to the last synched or recalibrated coordinates, which may be "off" slightly because of polar alignment error, equipment flexure, refraction, etc.


-----Original Message-----
From: [] On Behalf Of John Upton
Sent: Friday, April 16, 2021 8:31 PM
Subject: [ap-gto] #Mach2GTO #APCC #Absolute_Encoders

Hi Everyone,

Being new to Astro-Physics mounts and hampered by cloudy skies since getting my Mach2 a couple of weeks ago, I
have a bunch of small questions. I'll be asking these over the next few days.

Here is Question #1:
What is the difference between the Mach2 Home and Park-3 positions?

I have noticed that if I tell APCC to Find home (from the AE Tab) and then query its position (from the GoTo/Recal
Tab) it gives me position almost exactly as I expected -- Alt/Az is equal to my Latitude and Azimuth of 0. The mount is
not parked after this Find Home operation but tracking is turned off.

Now, If I Park the mount to Park-3 using the Park Tab of APCC, the mount will slew ever so slightly -- practically
invisible to the eye. However after this miniscule slew, if I again query the mount's position as before, I see that the
reported position is ever so slightly different from that reported after the Homing. The reported Alt/Az now shows the
altitude a little off a tiny amount from my Latitude and the Azimuth is now up to 10 arc-seconds from 0 and seems to
vary from one Park to the next.

What I have read in the manuals, says the Find Home is highly accurate and is set via the encoders at the factory.
That is easy to understand. However, why is this not consider to be the same physical position as Park-3?

It's not like this is terribly important because the difference in positions is tiny but why is there a difference at all?


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