Tag Archives: M27

Polar Alignment and TPoint model

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Clear tonight, but not dark until quite late.  (Duh. That’s what I get for re-starting the observatory only a few days after Solstice.)

I did new polar alignment tonight:

  • The “rough polar alignment” featur in TheSky, which slews to a computed star position which you then correct by adjusting the mount alt and az controls;
  • Then a TPoint model, about 40 observation points around the sky (semi-automated with camera and TheSky “Image Link” feature);
  • Then, with the TPoint model calculated, it makes an  “accurate polar alignment” feature available, which uses another star and continuous imaging to fine-tune the alt/az positions.

After that I did a few test slews.  Slewing to M27 from far away, it landed dead-on, precisely centred.

Just for fun I did a quick 60-second exposure while I was there.  It looks pretty good, so I’m hopeful I’ll see improvements.  This image is uncorrected (no darks or flats) and, more important, has no Periodic Error Correction running.  PEC training will be my next evening’s activity.  I won’t really know how the mount is performing until I see that Periodic Error graph.

Added some Hydrogen-Alpha to M27

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M27-Ha-L-RGB-CompositeI had captured an hour of high-res Ha data a month ago, on the same evening as when I captured the Luminance, but hadn’t done anything with it.

Here the Ha is mixed in with Luminance, increasing the intensity of the gas envelope in the nebula. The colour balance came out a little different, but I rather like it so I’m leaving it as is.

Now we’re getting somewhere

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Lum-Median-LRGBBacking up and re-focusing on some basics has paid off. I’m quite pleased with this first result on M27. This is 4 hours of data over about 2 weeks, 1 hour each of LRGB, with RGB binned 2×2. QSI 583 camera on an AT8RC, autoguided with a Lodestar, on a G11.

What I did differently to make this result better than previous ones:

  • Better autoguider and more attention to guider settings
  • One colour per session, taking time and not rushing
  • Focused for each filter
  • Flats for each filter, immediately after the data gathering, so filters are certain to be in exactly the same spot
  • Normalized & stacked with CCDStack, basic processing in Maxim, more processing in Photoshop.

The problem is, this is quite addictive.  Now I want more data – several more hours of each, and I can see never being satisfied.  More data to follow when the clouds leave.

Replaced Guide Camera, and Took a Step Back

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I’ve been frustrated with my guiding performance for some time, getting elongated stars and soft contrast, and decided to slow down ad tackle this.

I replaced the guide camera with a Lodestar which mounts rigidly to the main camera’s guide port using a threaded C-mount. There is no flexure at all in this arrangement, and the Lodestar’s sensitivity produces better guide stars.

I also switched to guiding with separate guide software (PHD) since I was worried about an effect when guiding with Maxim: it doesn’t use a separate process for the guiding action, so during the QSI583 camera’s long download time (30 seconds for a large 1×1 image), Maxim is blocked and not guiding.

This arrangement seems to work well, and I’m getting good round stars in 5- and 10-minute images. Continue reading →

Nov 10: More M27, start 2 new targets

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Tonight looks like a repeat of last night – the sky is clear and the CSC says excellent transparency all night. I’ve opened the dome at 7:30 PM, and am taking another 2 hours of M27 in 15-minute subs, to add to the data collected the last couple of nights.

I just noticed that for the first 500 seconds of the first 900-second sub, I forgot to turn PEC on. It was still guided, but more correction needed than I would have liked. So I may end up discarding this first sub – we’ll see how it turns out. The other 1.75 hours will be PEC-corrected in any case.
Sure enough, in post-processing Maxim recommended discarding the first sub (and another) for poor star-roundness, so I went along with this. The result, with 4.5 hours of data, is starting to look nice – detail in the outer gas envelope is beginning to show well.

Continue reading →

Clear night: More M27 time and some other targets

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November 9, 2010. The moon has set and, with DST over but no snow cover yet, it is surprisingly dark in my back yard. It’s clear and not too cold – about 5 degrees.

2010-11-08-M27_0Gathered 2 more hours of data on M27, this time in 15-minute subs. I’ve bumped this up from 10-minute subs just to see the effect. I would expect slightly deeper results, and slightly better S/N, than with more shorter subs. On the other hand, the longer the exposures, the greater the chance that something like a passing plane will ruin them. So I’ll try 15 and see how that works, and maybe push even longer for the next run.

Watching the guiding graph, I note that RA guiding is still tending to oscillate back-and-forth across the zero axis, so I have tried turning the x-aggressiveness down a bit, to 60%, to see if it can further smooth out the curve. Watching the results for a couple of minutes, it does seem to have resulted in a flatter error curve. Continue reading →

Improved Periodic Error and some M27 Data

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The CSC predicted clear skies last night, but reality disagreed, and it was completely overcast. Tonight seems better – the sky is clear and steady, and it’s dark earlier because today is the day we went off Daylight Savings time. It’s cold out – 1 degree Celsius.

Yesterday during the day I adjusted the RA worm gear, increasing the slack to the OVision specs, hoping that will improve the Periodic Error of the mount, so tonight I am doing a PEMPRO run to get new PE data and generate a new PE Correction curve. I’ve just started a 15-minute data gathering run, and am typing this from inside while the data collect.

The initial run gave under +/- 4” error, with a reasonably repeating curve (which already seems better than the rather ragged guiding track I was seeing the other night, before adjusting the RA slack). Better, the frequency plot of the error showed it is largely periodic on the worm cycle, so it will respond well to PEC. So I uploaded a calculated PEC set to the mount, and did another data gathering run with PEC turned on.

Oops. The new run had a weird spike in data right at the start, and I realized that I had slewed the scope but then not taken the slack out of the RA gear. So it took until the RA drive “crossed the gap” of the RA backlash before accurate tracking was underway. Lesson learned, and I started the run again.

Great results – PE with correction is now showing at +/- 1.1”. Continue reading →