Trapezium Cluster (Theta-1 Orionis) and ASI290MM for DSO Trial

My objective last night was to image the Trapezium Cluster with the ASI290MM to determine its DSO imaging capability. I found that it is not suitible to me for this purpose.

It had been windy all day, but the wind had died down as sunset approached. Brought the camera and power board out at round 1700 to set up and power for remote imaging later. There was no threat of dew or frost, and the temperature was about 34 degrees when I went out to start the imaging session. Seeing was noticeably bad, which says a lot considering that I rarely detect bad seeing when working at the TV’s 540mm focal length.

Equipment configuration consisted of the ASI290 on the back of the flip mirror without the 2.5x power mate. I was not configured for guiding, because it was colder than I would have liked for sitting beside the scope to calibrate and get it going. Also, I wanted to use the top port on the mirror box for the eyepiece to help quickly locate my primary target. This was a smart move because I spent only a few seconds on this task in spite of opting to use a week-old polar alignment instead of doing a fresh one beside the scope, and in spite of not doing a star alignment. Big time saver here.

After dinner, I needed to wait an additional 15 minutes for Trapezium to cross the meridian, then I went out side to start working at about 1950.

I found that the Trapezium was much smaller that I had expected. Even though I checked object scale vs sensor frame size in Stellarium, I expected that the four main stars would nearly fill the sensor frame at prime. That is why I took the PM out of the path. To my surprise, it was very tiny in the frame. I set a very small ROI and imaged it in four video captures of 500 frames each though the L filter only. The gain setting for all four runs was 412 db. The durations were 6.5, 17, 32.5 and 65.4ms. I think that I could see just one additional star in the live display. Maybe one of the video captures will reveal more after stacking, stretching, and maybe I will even try sharpening. The TV is not the right tool for this job. The Meade would have been much better for getting a decent image scale. I am happy that I thought to write down the capture data so that I could include it in this report.

I then went to max frame, and could see most of M41/42, and did a 300s single frame capture. The gain was 0 db, so 300s is about as long as I could expose with this setup without washing out the frame. As expected, I had serious star elongation, because my polar alignment was suspect, and I was not guiding. While Firecapture can do minutes-long single frame exposures, this is a very difficult tool to use for this purpose, and I would prefer not to use it for assessing your mount. Image to come after I process.

Using the wrong tool for the job taught me a lot. For pulling out additional Trapezium stars, the Meade is the right scope. I think that using a planetary camera behind the Meade to do higher gain, high speed video captures will be the best way to pull out the additional dimmer stars.

I also learned that the ASI290 can do DSO photography, but like the ZWO clearly states, the planetary cameras excel at planetary, but are not as capable for DSO.

M42 Orion Nebula - 2022-02-19 01:42 UTC - Test Shot
The Great Orion Nebula
Trapezium - 2022-02-19 01:54 UTC
Trapezium Cluster in The Great Orion Nebula

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