Re: PEMPro Data gathering


Mike Shade
 

Hi Mike,

1600GTO, early model (just had bearings replaced in RA/DEC gear boxes), Planewave CDK 17/unbinned image
scale .631"/pixel/permanent setup
Is it best to gather data at 0 dec (about 55 degrees elevation), or higher (80 degrees) to minimize seeing effects?
55 degrees elevation is more than good enough for measuring periodic error. If you want to minimize seeing issues, try waiting until early morning, a couple of hours before dawn, and start collecting data then. Usually localized seeing effects from the scope, the ground, and nearby structures are minimal as they have had the whole evening to normalize to the temperature.

Doing 10-12 cycles, as Bryan suggested, might help produce a more accurate result. However, don't go too long much longer because if the drift becomes too complicated, it can't be entirely separated from the PE data and can be detrimental to getting the most accurate PEC curve.

I generally get 400 points or more, that is something like 5-6 cycles. Will try a longer data gathering time and see what that does.

To minimize seeing effects, better to use a shorter exposure, say .25" and a longer delay between exposures, say
3" OR a longer exposure and longer delay (1" exposure/3" delay)?
There is a tradeoff here that depends on the cycle time of your camera. If the camera takes 2 seconds between exposures, you don't want to use a 0.25 second exposure because you are only sampling the star for 0.25 seconds every 2 seconds. You might want to choose a two-second, or three-second, exposure. That would capture the star 50% or more of the time. However, if you can use a video camera (on a brighter star), there is no harm to collect data at video frame rates.

The camera cycles pretty quickly as it is a pretty small portion of the whole frame. I can do say a .25" exposure and a .25" delay easily, or even quicker if need be.

-Ray Gralak
Author of PEMPro
Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro
Author of Astro-Physics V2 ASCOM Driver: https://www.siriusimaging.com/apdriver

-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Mike Shade
Sent: Sunday, November 15, 2020 7:28 AM
To: main@ap-gto.groups.io
Subject: [ap-gto] PEMPro Data gathering

Have a few questions on best practices for PemPro data gathering.



1600GTO, early model (just had bearings replaced in RA/DEC gear boxes), Planewave CDK 17/unbinned image
scale .631"/pixel/permanent setup



Is it best to gather data at 0 dec (about 55 degrees elevation), or higher (80 degrees) to minimize seeing effects?



If higher data gathering, calibrate here as well?



To minimize seeing effects, better to use a shorter exposure, say .25" and a longer delay between exposures, say
3" OR a longer exposure and longer delay (1" exposure/3" delay)?



When gathering data, I can watch the star in Maxim move quite a bit off of centroid in random directions. Some is
of course real PE, the rest noise. I know the program can account for this to some extent, but this is a lot of noise
and wonder if it is being represented in the final curve.



Generally get about 400 points for a PEC curve, more or less.



Thanks.



Mike J. Shade

Mike J. Shade Photography:

mshadephotography.com



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