Re: 3-4" RA wiggling while PHD2 guiding with EXOS2-GT PMC-eight #EXOS2 #astrophotography

Doug Doonan

HI Jerry,
This straightens me out on the formula and how it works. Pretty neat. Also, thanks for the chart. It will be handy in my set-up.
Boy, all I can say is that this astronomy stuff is complicated, and people have done the math to analyze it.
Doug D.

-----Original Message-----
From: Jerry Hubbell - Explore Scientific VP Engineering <jrh@...>
Sent: Thu, Jan 14, 2021 1:59 pm
Subject: Re: [ESPMC-Eight] 3-4" RA wiggling while PHD2 guiding with EXOS2-GT PMC-eight #EXOS2 #astrophotography

There are 206265 arc-seconds per radian so the formula is the conversion between an angular value to a linear scale at the image plane. The value is 206.3 (rounded 206.265) because of the FL being in mm and the pixel size being in um (microns) a 1000:1 ratio.

I hope that makes sense.
Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at
1010 S. 48th Street
Springdale, AR 72762

Author: Scientific Astrophotography: How Amateurs Can Generate and Use Professional Imaging Data
             Remote Observatories for Amateur Astronomers: Using High-Powered Telescopes From Home

Mark Slade Remote Observatory (MSRO) IAU MPC W54 Equipment
Wilderness, VA
: ES PMC-Eight G11 + Telescope Drive Master (TDM)
Scopes: ES 165 FPL-53 ED APO CF, ES 102 FCD100 ED APO CF
Cameras:  QHY174M-GPS + FW, QHY163C
Misc: 3-inch 0.7x Focal Reducer Field Flattener, Filters: Luminance,
Red, V-band Photometric, Diffuser, 200 lpmm Spectral Grating

Software: MaxIm DL 6, Cartes du Ciel, Astrometrica, AstroImageJ, AutoStakkert!


Doug Doonan
HomeBru  6 inch Reflector  f 6.6
HomeBru  85 mm Refractor  f 5.6
Long retired EE.

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