Siril Photometric Colour Calibration

Siril is very easy to use for processing astro-images. One think I’m never sure about is the colour calibration step that requires me to pick white and black sections of the image. It turns out that Siril has a built-in function that can look at what section of the sky you’ve photographed and correct your colours. I tried it on my image of M31 from the other night and it’s a bit tricky to start up but it did seem to work well. The image below is per Siril PCC plus a little bit of raising the black point with the asinh function. I feel like it’s a bit greeny compared to my best effort. Bumping the saturation up just made it worse – I actually prefer my previous version right below it.

I’m looking forward to trying this on the ring and dumbbell nebulae though, next clear night.


Milky Way Lucky Shot

We spent a few days at a cottage in the mountains. Very dark skies overhead although hemmed in by forest. I was delighted to see the milky way easily although not as vivid as in the image above. That is the result of four 30 second shots at ISO 1600 through the canon 18-55mm lens at 18mm f/3.5. This was just the camera on tripod, no tracking, no zoom.

Cassiopeia is lost in the profusion of stars but it was clear in person. Andromeda shows just above the trees right of centre. In one of the sub-exposures I caught a late perseid meteor just above Andromeda. I saw another one around the same time. For the image below i took the sub where i caught the meteor, duplicated it so i had three copies then fed it to Siril. Besides the usual process I used the ASINH transform to move the black point about half way.

A Quickie In the Backyard (With M31)

This is not very good, of course but it was very easy. I was a bit surprised to find that i had a clear line of sight to Andromeda last night around 10:30 pm but it was almost 30 degrees up so maybe not unexpected. I just took 3 shots at ISO 400, 60 seconds each through the takumar 200mm lens wide open at f/4. I combined the 3 shots with Siril as below. You can pick out M110 and M32 if you know where to look but I left a lot of detail on the table. It will only get higher in the sky from here so if i take my time i can do a lot better. This is about a 25% crop.

Siril workflow(from
-Lights into desktop\20-08-07\lights
-Siril change directory to desktop\20-08-07
-Script DSLR preprocessing no darks no flats no bias
-B/W window to autostretch
-image processing/color calibration/color calibration
-image processing/remove green noise
-B/W window to linear
-Image processing/histogram: autostretch
-Image processing/asinh transformation: moved black point half way to the right
-cropped and saved as JPG

M33 – The Triangulum Galaxy

20-01-04 M33

This is a very sad sort of thing to be pleased with, but I am!  On the left is the Triangulum constellation with alpha Triangulum near the center bottom, in the right top corner is Mirach in Andromeda.  The faint puff of gray off to the right about 1/3 of the way from alpha Tri to Mirach is the Triangulum galaxy!

This was 7 shots at 30 seconds with the Canon T3i, 50mm lens at f/2.8, and ISO 800.  The shots were stacked with Deep Sky Stacker then adjusted with Rawtherapee.  I picked the best 7 of 9 shots to stack and used the recommended parameters, in Rawtherapee I just played with the various sliders.  Black point is set to 5176, Shadow Compression to 0, Lightness to -6, and Contrast to +61.  All of those had some effect but Black and Shadow Compression probably the most.

My plan had been to shoot for 60 seconds at f/3.5 ISO 800 which is a bit more light but there is too much sky glow in my back yard.  My best shot of Bode’s Galaxy and the Cigar Galaxy was 60 seconds f/4 ISO 400.

The thumbnails below are just reminding me what the DSS and Rawtherapee screens look like:

UPDATE: Below is a further overprocessed image from rawtherapee and the corresponding settings. I note that in the original image I could see a bit of M31 the andromeda Galay in the top right. If I could reliably frame the two galaxies in would be an interesting image. Also, the jumble near the center of the original is NGC752 – an open cluster.

Meanwhile Back in Nikonia

I was out one night earlier in the month trying to image M31 with the Nikon P900.  The results were pretty dismal.  Below are my three best tries.  The first one is from a starscape video so 25 sec ISO 100 and the others are ISO 6400 1/2 sec.  In each case you can see the Andromeda Nebula as a smudge.  The smudge is pretty blocky in the video frame.   I looked at a number of the frames and they were similarly blocky so i doubt that stacking would make a difference.  So the Nikon makes night sky photography easy and fun but not that rewarding – the sensor is just too small.

DSCN2006_Moment (3)DSCN2035 (2)DSCN2034 (2)


19-10-29 M31 135mm 4106 (2)

I was out again last night with my 135mm lens but without a dew heater so I got better resolution on M31 but not as sharp as it could be.  This is a combination of 8 not-too-smeary shots at with the canon t3i at 135mm f/5.6 75 seconds ISO 1600. I stacked and stretched it with pixinsight following Alan Hall’s book then decoloured and dimmed it with the windows photo tool.

The image below is 8 shots at ISO 3200, 37 seconds, 135mm.  I did this hoping the lens would get less smeary between wipes.  I haven’t decoloured it and the crop is a bit different but, if anything the longer subs are better.


M31 135mm iso3200 4116

Androm-again – And Is She Stacked!

19-10-24 stacked M31-cropped

I am pretty pleased with this result.  Eleven images 60 seconds each at f/3.5 ISO 800 shot at 50mm and cropped.  Processed with pixinsight using guidance from Alan Hall’s book. After stacking with pixinsight The image had a greenish tint and I eliminated that by using the color slider in the windows photo tool, then used the brightness slider to reduce brightness a bit.  That’s a crude tool but i’m happy with the result.

Above M31 you can see M110 and the greyer “star” below it is M32.  The two brighter stars  midframe are v Andromeda and 32 Andromeda.  Near the bottom center us u Andromeda.

Below, for reference is IMG_3963, one of the 11 frames stacked to generate the picture in its original size and roughly cropped to match the above.

I now have a 135mm lens which I intend to try on the next good evening.  Assuming I can do 60 second exposures I would need higher ISO to get the same brightness because the lens is f/5.6 rather than the 3.5 I was using for the above.  According to this I think the brightness ratio is (5.6/3.5)^2 or about 2.5 so I will try ISO 1600 for 75 sec and if that’s no good, ISO 3200 for 37 sec.

Tracking Andromeda


That’s M31 – the Andromeda Galaxy – front and center. Mirach and Alpheratz are toward the bottom.  This is a combination of five images shot at 10 seconds f/4 ISO 1600 using the Canon t3i with 50mm f/2.8 lens. The five images were combined with DeepSkyStacker then brightened with the Windows Photo tool.  The sky was visually dark although it shows blue-grey above.


The Camera was mounted on my new-to-me ioptron Skytracker. I didn’t have a lot of luck aligning the tracker with Polaris, my vision is pretty poor at night, but I’ll keep trying.

At Last! A Smudge!

No exactly epic but I’m pleased at how my camera pointing skills are progressing.  This was taken at the dark sky site with the Canon T3i, the 18-55 kit lens at 55mm f/5.6, 10 seconds at ISO 1600. The two yellow blocks are u and v Andromeda.  I was pointing the camera using Cassiopeia as my anchor point.


19-08-03 andromeda 3583

Another camera pointing exercise:  Back at my home base I was using the SkyView app on my phone to point at M31.  The image was taken with the Canon T3i using a 24mm f/2.8 lens – 15 seconds at ISO 800.

19-08-05 andromeda 3636