AstroTanja
M42 is a glorious mix of diffuse nebula and one of the the brightest nebulae in the sky. It’s a wonderful target for novice and experienced imagers as there’s always more data and detail to find. It’s easy to capture – but difficult to master.
For this image I used the HDRcomposition function in PixInsight to preserve the inner core of the structure. I only shot 2 exposure series of 60 seconds and 240 seconds. I think I could have further retained more detail had I shot 30/45-second exposures for integration as well. Similarly, with long exposure, had I added 8/10 minute subs to this, the other feint data would have shown through. From the final image, however, you will notice that some dark nebula does show through.
Here’s the PixInsight forum link on the HDRcomposition I followed (click here), it’s also an example of M42 which proves advantageous.
I’m surprised about the data I did manage for a total integration time of 3:16hrs. I shot this prime focus on my APO from an extremely light-polluted sky in Johannesburg’s suburbs, no use of any LP filters. (Granted my APO is renowned for its colour quality, but the result was very impressive in the brightest spot in Africa.)
M42 is an easy target as it’s the brightest diffuse nebula in the sky, but I also dedicated a lot more imaging time to the target than I have with most. Ideal imaging position in my sky only starts at 1/2am (October), so I split the total over 2 nights. (I set up early and catch some sleep beforehand)
Total: 196min (3:16hrs)
40x 240sec ISO400
36x 60sec ISO400
20 darks
100 bias
30 flats
Calibration frames
If you’re not shooting these already, it’s time to start. Darks, flats and bias frames will assist with improving your lights, resulting in an overall better image with less noise and even illumination.
Processing M42
This is a single 240sec (auto stretch applied) image that has not been calibrated with flats/darks/bias frames.
This is a single 240sec (auto stretch applied) image that’s been calibrated with flats/darks/bias frames.
This is the 40×240 integrated calibrated image / stacked.
This is the 40×240 second and 36×60 second integrated with the HDRcomposition tool. (Auto stretch applied) 
The workflow used for this image:
PixInsight
Light frames calibrated with bias/dark/flats, debayered and aligned. (The 60 and 240 second subs had their respective calibration frames). The final 60 second integration, and 240 one – were then aligned and combined with HDRcomposition.
Processing: Crop / DBE / Colour balance / Histogram Stretch / HDRmultiscale / followed by a series of curves adjustments & histogram stretches with star & range masks applied / ACDNR and further stretching and sharpening.
Photoshop
Further level adjustments / saturation / selective layer sharpening.
Equipment Used;
Canon 60Da
Officina Stellare HiperAPO105
Celestron Advanced VX
Guiding: SSAG & PHD
Acquisition: Nebulosity
Processing: PixInsight and PhotoShop
Here are some previous attempts of this target when I first started out in astrophotography (about 18months ago):
M42 imaged through my 80mm Celestron Guide Scope >click here<
M42 Imaged with a C11′ SCT >click here<
…Thanks for reading this 🙂
Haha, baie dankie 🙂
How do you determine the number of calibration frames to use?
I go by various forum posts I’ve read, and experience with some of my targets. Generally 10 bias frames for each dark frame, and the more dark frames you have the smoother your image will be. I’ll stick with 20 – 30 dark frames per target, it definitely gives a better result than 10 dark frames, but it’s also very much dependent on the target. 30 Flats integrated also gives you a good average to fix any uneven illumination. These are general numbers I stick with.
Second question: Do you plan on doing a guide to your post-processing procedure? I understand a few things you talk about, but I don’t have extensive knowledge of Photoshop. Or do you recommend a guide that encompasses most of what you do post? Thanks! Love your images and blog entries!
Hmm, I’ll do a blog post on post-processing. It’s an interesting subject. Thing is many people have different ways, I don’t believe in right/wrong, as long as the end result is correct. I use a mix of PixInsight and PhotoShop and will gladly write something up. It’ll appear here over the course of a few days.
Jy mag maar! Stunning!