Guiding - IC434 with Ha filter

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turfpit
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Guiding - IC434 with Ha filter

#1

Post by turfpit »

About this time last year I attempted to get PHD2 going. All I managed to do was to convert stars to hyphens! I have now had another attempt. Having discovered that PHD2 has a 'Simulator' mode, I was able to work through the steps to learn how to use the software while reading the manual in the warmth and comfort of my study.

The plan was to take several single guided exposures of IC434 using an Ha filter - exposures used were 2m, 5m, 10m, 15m, 20m, 25m. This is the result of stacking the 5, 10, 15, 20, and 25 minute exposures:

IC434-5-frames-Ha-filter-guided.JPG
IC434-5-frames-Ha-filter-guided.JPG (66.4 KiB) Viewed 851 times


The image is noisy and would have benefitted from more dark frames plus stacking of more frames of the same exposure. The object of the session was satisfied in that I had some reasonable length guided exposures and the equipment plus cabling had been validated.

This is a comparison of the frames captured (images as displayed in FITS Liberator with no stretching):

exposure-comparison.JPG
exposure-comparison.JPG (229.31 KiB) Viewed 851 times


Observations:
  • The 2m exposure through the Ha filter was a waste of time.
  • By the time the 20m exposure was in process, Orion was hanging directly above Manchester City Centre. A good test to validate use of narrowband filters when light pollution is present.
  • The 25m frame has poorer quality compared with the 20m frame. By this time Orion was setting and the belt stars were at an elevation of around 30°.
  • For the full session of 1h 15m the guiding software was running. There was no drift of the object. The stars look fairly round which suggests the guiding was working.
This is a comparison of the histogram for each frame:

histogram-comparison.JPG
histogram-comparison.JPG (38.63 KiB) Viewed 851 times


Observations:
  • 2m and 5m exposures are hitting the left hand side, meaning some faint detail is lost.
  • The 20m exposure has a clear offset from the left hand side, meaning that no faint detail has been clipped.
  • If I get the opportunity I will carry out a comparison between 12x10m and 6x20m but this might have to be next year.
This is the state of the PHD2 guiding screen at the end of the session:

PHD2-end-of-session.JPG
PHD2-end-of-session.JPG (66.85 KiB) Viewed 851 times

  • I used an ST4 connection - camera ST4 port directly connected to mount auto-guide port. This seemed a simple way to get started and avoids another cable having to be connected to the capture laptop. This ST4 configuration means that calibration would need to be carried out if the telescope was slewed any distance. With this type of imaging, it is unlikely that multiple targets would be imaged in a session.
  • I ran calibration, reviewed calibration.
  • I ran the Guiding Assistant and applied recommended settings.
  • Commenced guiding using the guide star selected by the software, using a 2s exposure.
  • I need to work on improving the RA/DEC graphs. Part of the issue could be scope balance with the target low in the west. Also poor seeing for the low elevation may be a factor.
Using the PHD2 simulator. For the development, in the PHD2 profile, camera was set to 'simulator' and the mount to 'on-camera'. For the simulation, no guide camera was attached to the laptop.

PHD2-simulator-running.JPG
PHD2-simulator-running.JPG (101.93 KiB) Viewed 851 times

PHD2-profile-settings-for-simulator.JPG
PHD2-profile-settings-for-simulator.JPG (44.58 KiB) Viewed 851 times


This is the assembled equipment (a no-longer-in-production refractor and 10 year old CCD camera):

scope-and-camera-plus-guider.JPG
scope-and-camera-plus-guider.JPG (41.91 KiB) Viewed 851 times


Notes:
  • The guidecam is rigidly bolted to the scope carrying handle. This should avoid any flexure.
  • The 2 camera USB2 cables are swept back and cable-tied above the dovetail. This avoids any dragging cables causing imbalance.
  • The 0.67x reducer has a back focus of 63.5mm. The 60mm to T2 adapter uses 8.5mm. The remaining 55mm was made up of 15mm for the filter drawer, 12.5mm sensor set back from camera window and various T2 extension tubes.
  • I used 2 old socks with the toes cut off to keep the extension, filter and camera window from fogging up. This has worked well for me as I live in a damp climate and a voids having to have dew heater bands and the extra cabling & power requirement.
The QHY mini-guide-scope worked well.

Next steps will be acquire 2 hours of Ha images, probably using 20m as the exposure for a frame.

Dave
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oopfan
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Re: Guiding - IC434 with Ha filter

#2

Post by oopfan »

Dave,

Outstanding write-up!

Brian
Last edited by oopfan on Mon Mar 29, 2021 10:51 pm, edited 1 time in total.
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turfpit
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Re: Guiding - IC434 with Ha filter

#3

Post by turfpit »

Thanks Brian. The ST4 project looks interesting - a combination of hardware and software skills - good luck with this.

Dave
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Re: Guiding - IC434 with Ha filter

#4

Post by admin »

Hi Brian,

I think the mount puts out voltage on the ST4 direction pins and the camera signals that direction by allowing the current to flow to the mount ground (also coming via the ST4 cable) - see https://github.com/kevinferrare/arduino-st4/

cheers,

Robin
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