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3-4" RA wiggling while PHD2 guiding with EXOS2-GT PMC-eight #EXOS2 #astrophotography
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Walter:
You may want to check out this website that has astronomy related calculations. -- Sincerely, Jennifer Shelly AstroPorch, VA Mounts: ES PMC-8 G-11, ES PMC-8 iEXOS-100 Scopes: ES ED127 FCD-100, Askar FRA 400, ES Levy Comet Hunter, ES N208CF, QHY Mini Guide Scope, Solomark F60 Guide Scope Cameras: QHY600M, QHY128C, QHY168C Misc: MoonLite CFL 2.5 / High Res Stepper / V2 Mini Controller, Baader SteelTrack NT / SteelDrive II, Baader UFC, Optolong 2" L-Pro / L-eNhance, QHY CFW3-L, Baader 2” LRGBSHO CCD Imaging Software: NINA, APT, SharpCap Pro Processing Software: PixInsight, Lightroom, Premiere Elements
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That's just a scale/unit conversion - the number of arcseconds in a degree (3600) divided by the number of microns in a mm (1000).
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Doug Doonan
Hi Bassliner,
Thanks for the info.
And where does the 3.6 come from?
Doug Doonan
-----Original Message-----
From: Andreas Volz via groups.io <bassliner303@...> To: MAIN@espmc-eight.groups.io Sent: Thu, Jan 14, 2021 1:23 pm Subject: Re: [ESPMC-Eight] 3-4" RA wiggling while PHD2 guiding with EXOS2-GT PMC-eight #EXOS2 #astrophotography Hey Doug,
The formula is:
pixel size (microns) x 206.3 /focal length in mm = image scale in arcsec/pixel
206.3 results out of:
3.6 * (180 degrees / pi) = 3600/1000 * (180 degrees / pi) = 206.26
-- Clear skies, Andy
Mount: ES PMC-8 EXOS2, ioptron SkyGuider Pro Scope: SkyWatcher Explorer 150/750 PDS Cameras: Canon 6D, Canon 7D Mk2 Guiding: ZWO ASI120Mini mono, ZWO 30F4 Guidescope, PHD2 Msc: TS Optics Coma Reducer Corrector 0.95x Software: N.I.N.A, APT, Pixinsight, DeepSkyStacker, Photoshop -- Doug Doonan HomeBru 6 inch Reflector f 6.6 HomeBru 85 mm Refractor f 5.6 PMC-8, EXOS 2 Long retired EE.
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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@...> To: MAIN@ESPMC-Eight.groups.io 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 explorescientific.com www.explorescientificusa.com 1010 S. 48th Street Springdale, AR 72762 1-866-252-3811 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 Mounts: 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 PMC-8, EXOS 2 Long retired EE.
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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 explorescientific.com www.explorescientificusa.com 1010 S. 48th Street Springdale, AR 72762 1-866-252-3811 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 Mounts: 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!
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Harry
Doug, here is a table that might help. Otherwise Peter Zelinka on You Tube explains the formula in his video choosing your first dedicated astronomy camera.
-- Harry Vero Beach, FL Mounts: ES iExos 100-PMC Eight Scopes: ES ED80CF, ES AR102, Meade ETX 90 EC (Deforked) Guide: ZWO 30mm Mini, ZWO ASI120MM-Mini Software: ASIair Pro, iPad Pro, MacOS, Starry Sky Stacker, Affinity Photo, Lightroom, SkySafari Plus Cameras: Nikon D600, D5500 Misc: ES USB Power Bank, Rigel QuikFinder, 0.8x Focal Reducer Filters: Optolong L-Pro, L-eNhance
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Walter Vinci
Thank you all for your help,
toggle quoted messageShow quoted text
I will try switch guiding from my guide scope (162 mm) to my imaging scope (480) and see if guiding improves next time I have clear skies. That will give my a pixel scale of about 2.2 arc-seconds. Best, Walter
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Andreas Volz
Hey Doug, The formula is: pixel size (microns) x 206.3 /focal length in mm = image scale in arcsec/pixel206.3 results out of: 3.6 * (180 degrees / pi) = 3600/1000 * (180 degrees / pi) = 206.26
--
Clear skies, Andy
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Doug Doonan
Jerry,
Where does the 206.3 in your formula come from, and what are its units?
Doug
-----Original Message-----
From: Jerry Hubbell - Explore Scientific VP Engineering <jrh@...> To: MAIN@ESPMC-Eight.groups.io Sent: Wed, Jan 13, 2021 8:34 am Subject: Re: [ESPMC-Eight] 3-4" RA wiggling while PHD2 guiding with EXOS2-GT PMC-eight #EXOS2 #astrophotography Hi Walter,
Yes, I would suggest a 2x Barlow or tele-extender instead of a 3x. The formula for pixel or plate scale is: Pixel Scale = (Pixel Size x 206.3) / FL, So for your combination: Pixel Scale = (5.2 um x 206.3) / 162 mm = 6.6 arc-seconds/pixel BTW, your calibrations look spot on, no problem there, -- Jerry Hubbell Vice President of Engineering Explore Scientific, LLC. jrh at explorescientific.com www.explorescientificusa.com 1010 S. 48th Street Springdale, AR 72762 1-866-252-3811 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 Mounts: 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 PMC-8, EXOS 2 Long retired EE.
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Hi Walter,
Yes, I would suggest a 2x Barlow or tele-extender instead of a 3x. The formula for pixel or plate scale is: Pixel Scale = (Pixel Size x 206.3) / FL, So for your combination: Pixel Scale = (5.2 um x 206.3) / 162 mm = 6.6 arc-seconds/pixel BTW, your calibrations look spot on, no problem there, -- Jerry Hubbell Vice President of Engineering Explore Scientific, LLC. jrh at explorescientific.com www.explorescientificusa.com 1010 S. 48th Street Springdale, AR 72762 1-866-252-3811 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 Mounts: 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!
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Hi Doug,
That would work if you get get the camera to the focus position with the Barlow or tele-extender. I would suggest trying it at 2x instead of 3x. -- Jerry Hubbell Vice President of Engineering Explore Scientific, LLC. jrh at explorescientific.com www.explorescientificusa.com 1010 S. 48th Street Springdale, AR 72762 1-866-252-3811 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 Mounts: 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!
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Walter Vinci
Hi Jerry, Thanks for looking at the logs. I went for the Orion guiding package because of its popularity. I thought it would be more than enough to guide my ED 80 at a 2 arc-sec/pixel imaging scale, but this seems will not be easy according to your comment. I should then use a Barlow lens as Doug suggest or use a guiding camera with smaller pixels if I wanted to push guiding to seeing/mount limits? Walter
On Jan 12, 2021, at 8:35 PM, Doug Doonan via groups.io <dougdwd@...> wrote:
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Doug Doonan
Hi Jerry and Walter,
Would it be possible to use a 3X Barlow in the guiding scope to increase the guiding to the 2 to3 arc-seconds you suggest?
Doug Doonan
-----Original Message-----
From: Jerry Hubbell - Explore Scientific VP Engineering <jrh@...> To: MAIN@ESPMC-Eight.groups.io Sent: Tue, Jan 12, 2021 2:11 pm Subject: Re: [ESPMC-Eight] 3-4" RA wiggling while PHD2 guiding with EXOS2-GT PMC-eight #EXOS2 #astrophotography Hi Walter,
I am just starting to look at your guide log, but I did notice that your guide camera (an Orion Starshoot Autoguider) with a 5.8 um pixel coupled with your very short focal length guide scope (162 mm) makes you image scale very large at 6.6 arc-sec/pixel. This is a big problem if you are trying to auto guide to < 2-3 arc-seconds and is very difficult to get any better performance. This will especially the case if you seeing is poor. I will spend some more time looking at your guide log to see if I see anything else. -- Jerry Hubbell Vice President of Engineering Explore Scientific, LLC. jrh at explorescientific.com www.explorescientificusa.com 1010 S. 48th Street Springdale, AR 72762 1-866-252-3811 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 Mounts: 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 PMC-8, EXOS 2 Long retired EE.
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Hi Walter,
I am just starting to look at your guide log, but I did notice that your guide camera (an Orion Starshoot Autoguider) with a 5.8 um pixel coupled with your very short focal length guide scope (162 mm) makes you image scale very large at 6.6 arc-sec/pixel. This is a big problem if you are trying to auto guide to < 2-3 arc-seconds and is very difficult to get any better performance. This will especially the case if you seeing is poor. I will spend some more time looking at your guide log to see if I see anything else. -- Jerry Hubbell Vice President of Engineering Explore Scientific, LLC. jrh at explorescientific.com www.explorescientificusa.com 1010 S. 48th Street Springdale, AR 72762 1-866-252-3811 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 Mounts: 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!
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Walter Vinci
Hi Everyone,
I am pretty new to the hobby, jus went out a few times with my EXOS2-GT PMC-eight. My first struggle with this mount was a ~ 3-4" wiggling in RA I could not get rid of. RA basically kept jumping up and down by about that much every few seconds, with and without DEC guiding. Can seeing be so bad to cause that much error? Or is it more likely a mechanical problem with the worm gear? I have attached the PHD2 logs, hopefully it gives some hints and you can help me learn how to diagnose the logs (the logs contain multiple calibration and guiding sections, probably best to have a look at the latest data). Thank for the help, Walter
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