Behind the Image: The Large Magellanic Cloud

We don’t see a lot of LMC (Large Magellanic Cloud) images on the Internet…

By contributing author, Amit Ashok Kamble

…the major reason is that LMC is a southern hemisphere object. In the northern hemisphere, only observers that are south of about 20 degrees north latitude can see it.

To the naked eye it looks like a faint cloud of stars, as if the stars of Milky Way gathered together, but it is not. It is a small galaxy of its own adjacent to our Milky Way. To the camera, the LMC is treasure full of amazing objects and regions.

These images are a collaboration between Jonathan Green and myself. We planned the targets, Jonathan did the acquisition and I did the processing.

Location and acquisition

The image was shot during an annual astrophotography camp held at Foxton, New Zealand, November 2015. The sky conditions were okay, as it was not too far from a settlement. The only trouble that night was a party at the beach which had these massive party lights going across the sky.

November is the best month to capture good images of the LMC as the target is high in the sky, hence it was our target of choice.

Total exposure time: 30 minutes, 30 x 60 seconds ISO 1250 f/3.2
Camera: Canon 200mm f/2.8 lens, Canon 60Da
Mount: iOptron Skyguider
Calibration: 21 dark frames

If only the acquisition of these images was easy. We had a fairly good sky that night, but we were interrupted by clouds and unfortunately by party lights.

As you can see from the image, we had trouble at times when the light passed in front of the target. We could have given up imaging, but as an astrophotographer the first thing you have to master is patience. We waited for a while until the lights were turned off and that was when most of the data was captured.

Processing

I recently switched to PixInsight for all my astrophotography processing, and it is no doubt one of the best processing software packages out there.

Stacking, calibration and processing was done in PixInsight and was later exported to Adobe Photoshop for some final touches.

I followed a basic workflow from Harry’s Astroshed.

Workflow: linear stage

1. Batch Preprocessing to calibrate all R, G, B or OSC data
2. Refine settings with Image Integration (using calibrated data from 1)
3. Channel Combination to from an RGB image (not required if shot OSC)
4. Apply STF to single image for inspection (unlink channels if required)
5. Dynamic Crop to remove image defects
6. Dynamic Background Extraction (I spent time getting it right here)
7. Background Neutralization (should be after DBE)
8. Colour Calibration

Workflow: non linear

When going non linear don’t forget to disable the Screen Transfer Function!

1. Histogram Transformation to stretch image
2. HDR Multiscale Transform (if image requires it)
3. ACDNR for noise reduction
4. Histogram Transformation for black point setting and possible small stretch
5. Morphological Transformation for star reduction
6. Saturation Curve (with mask)
7. Local Histogram Equalization
8. SCNR to remove greens
9. Check background with Background Neutralization if colour changed during processing

Stand back and admire your work the next day!

…and then fine tune your image.

This is a really important step, wait one day before you post your image – you might want to make further minor adjustments!

The most challenging part during processing was not to overexpose the bright tarantula nebula and the galactic core and retain all the nebulous regions.

I obviously made few masks when processing, and they are a must. When you are working on targets like these without different exposure times for the brighter areas, you have to create masks to do some selective processing.

If you are wondering how I removed all the stars in Photoshop

After a lot of reading and browsing I found this awesome action by J-P Metsavainio. This helps a lot when you are working with nebulous regions and you want to reduce those stars, this action helps you control the brightness of the stars.

Here is another article that shows you how you can achieve the same in PixInsight.

My thoughts

Capturing images is the easiest part when deep sky imaging (of course, it’s not), but when compared to processing – it is.

Image processing is a learning curve and just cannot be learnt by watching few tutorials and reading articles. It requires a lot of practice and going over your images again and again, comparing different techniques to find the one that suits the target best.

I captured the LMC for the first time in 2014 and was really happy with the result. It was one of my best at the time but I wanted to learn more as I had seen better images of that region. I have upgraded my equipment since then, which really helped, but I have also patiently and persistently practised the art of post processing, and I’m still learning from other masters.

Below is a comparison of what I shot in 2014 and this one. My most recent image is a result of dedication, patience, persistence and practice.

Overall, if you are just starting out with deep sky imaging, don’t be disappointed if your images do not turn out like you expected. Astrophotography is a field where every image is going to look different, as it is subjective. Every person has their own style, so find the style that suits you the best.

Video tutorial

For processing details, watch the complete video tutorial on YouTube!

The final image

Data acquisition: Jonathan Green
Processing: Amit Ashok Kamble
Acquisition location: Foxton, New Zealand

About Amit Ashok Kamble

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About Jonathan Green

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