July 30: I was working on M51 data, but it eventually rotated below my hedge. I have a little time left, so decided to also start an M101 project, since it is well-positioned in my sky at this time of year.
This is the first set of Luminance, total of 1.5 hours in 10-minute sub-frames.
I’ve started a multi-night project for M51. July 28 was the first chance to catch Luminance data, 1.5 hours so far (in 5-minute subs). Sky-glow is fairly bad in this part of the sky (removed manually in the attached shot), and will require some careful processing as I get more data.
A satellite trail wasn’t completely removed via the median-combine. Once I get more exposure time, I’ll probably just discard the frame with the satellite.
Update: Problem in Colour Darks
I’ve had a couple of evenings chance now to gather colour data, and have captured R, G, and B, all binned 2×2, on separate nights. I was quite disappointed with the results – all are showing nasty black blotches. Looking for the cause of this, I believe my 2×2 calibration dark frames are faulty (I keep a library of darks at different reference temperatures and different exposure times, and think my 3-minute, -15 degree darks are bad).
It’s supposed to be cloudy for a few days now, so this will be a good chance to take new darks, then test those against the acquired data to see if that was the problem.
I 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.
Backing 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.
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