Behind the Image: M42 in the City

The Orion Nebula (M42) is easy to capture, but difficult to master!

M42 is undoubtedly one of the most popular deep sky targets. Whether you image through a telescope or a camera lens, it can be captured from anywhere on earth, by anyone who knows where to point their camera.

So imagine my surprise when my image of M42 was shortlisted for The Astrophotographer of the Year 2014 award!

What most people don’t know about this image is that I photographed it from my home in Johannesburg, South Africa, the most light polluted city on the entire African continent! I know – unbelievable, right? I did it without the use of any light pollution filters and with a Canon 60Da DSLR through my APO telescope.

So why do I think this image made the cut to get shortlisted, and why am so I incredibly proud of this achievement?

Simple. Dedication.

• Don’t use light pollution as an excuse – image anyway.
• Research the target you’re shooting, find out what other imaging techniques have worked well for others. In M42’s case it’s varied exposures to retain detail in the bright areas.
• Gather enough data, as much as you can! Every single additional sub exposure helps to increase SNR and allows you to bring out more detail. If the imaging conditions are right, take advantage of it, sleep can wait.
• Focus on post-processing! Superior processing skills can make images from most modest photographic equipment look superb.

M42 is a glorious mix of diffuse nebulae 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 detail to find.

How I acquired the data for the Orion Nebula

Equipment used to capture the data:

• Camera: Canon 60Da DSLR (currently discontinued, but Nikon has the D810a)
• Imaging telescope: Officina Stellare HiperAPO105
• Mount: Celestron AdvancedVX
• Guide scope: Orion SSAG, 50mm guide scope, and PhD
• Acquisition software: Nebulosity
• Processing software: PixInsight and PhotoShop

Acquisition details:

• Total: 196min (3 hours 16 minutes)
• 40x 240sec ISO400
• 36x 60sec ISO400 (for the core/trapezium)
• 20 darks for each exposure length
• 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. If you don’t know how to shoot flats yet, read this easy to follow tutorial.

This is a single 240sec image (with auto stretch applied) that has not been calibrated with flats, darks, or bias frames:

This is a single 240sec image (with auto stretch applied) that’s been calibrated with flats, darks, and bias frames:

This is the 40×240sec calibrated images, integrated (“stacked”):

This is the combined 40×240sec stack and 36×60sec stacks, integrated with the HDRcomposition tool (auto stretch applied):

Post-processing the Orion Nebula

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 or 45-second exposures for integration as well. Similarly, had I added 5 or 6 minute longer-exposure subs to this, the other faint data would have shown through. In the final image, however, you will notice that some dark nebula does show up.

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 managed for a total integration time of 3 hours 16 minutes. I shot this at prime focus on my APO from an extremely light-polluted sky in Johannesburg’s suburbs with no use of any LP filters. Granted, my APO is renowned for its colour quality, but the result is still very impressive considering I’m shooting from the brightest spot in Africa.

M42 is an easy target as it is the brightest diffuse nebula in the sky, but I also dedicated a lot more imaging time to the target than I have with any session prior to this. Ideal imaging position in my sky only starts at 1 or 2am in October, so I split the total imaging time over 2 nights. (I set up early and caught some sleep beforehand!)

Workflow: Processing in 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 and 240-second integrations were then aligned and combined with HDRcomposition.
• Processing: Crop / DBE / Colour balance / Histogram Stretch / HDRmultiscale, followed by a series of curves adjustments and histogram stretches with star and range masks applied, then ACDNR, and further stretching and sharpening.

Workflow: Photoshop processing

• Further levels adjustments
• Saturation
• Selective layer sharpening