PEMPro Data gathering
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Mike Shade
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:
In War: Resolution In Defeat: Defiance In Victory: Magnanimity In Peace: Goodwill Sir Winston Churchill Already, in the gathering dusk, a few of the stars are turning on their lights. Vega, the brightest one, is now dropping towards the west. Can it be half a year since I watched her April rising in the east? Low in the southwest Antares blinks a sad farwell to fall... Leslie Peltier, Starlight Nights
International Dark Sky Association: www.darksky.org
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Hi Mike generally you want the intersection of celestial equator and meridian. you want to avoid low altitude and near the poles exposure time doesn't matter as much - a few seconds is fine regarding noise, PEMPro does a great job of filtering that kind of stuff out. i'd say more cycles would help that. i typically aim for 12-15 cycles
On Sun, Nov 15, 2020 at 7:28 AM Mike Shade <mshade@q.com> wrote:
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Ray Gralak
Hi Mike,
1600GTO, early model (just had bearings replaced in RA/DEC gear boxes), Planewave CDK 17/unbinned image 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. To minimize seeing effects, better to use a shorter exposure, say .25" and a longer delay between exposures, sayThere 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. -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-----
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Mike Shade
Hi Mike,
1600GTO, early model (just had bearings replaced in RA/DEC gear boxes), Planewave CDK 17/unbinned image 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, sayThere 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-----
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