M3 – I’m Dithering!

Over-processed as always, this is 40 25 second shots at ISO 800 through the Z61(360mm f/6). Processed with siril’s photometric colour calibration then the black point raised .2. Of the 40 shots, 30 had dithering applied. That’s easy to do, just a button in Backyard EOS, but i can’t see that it made a difference.

Below is a comparo where i processed 10 images with no dither(ND), 10 with dither(D10), 30 with dither(D30) and the whole lot(ALL40).


The Rosette Nebula

This has been my great white whale for the last couple of months. It’s in the south in the winter which makes it tricky from my back yard. Last night I went to a nearby park where I have a view to the south over farmland. With the snow gone I was able to get 30 100 second subs at 800 ISO through the william optics z61(360mm f/6). I had to stand for the better part of an hour blocking a streetlight but it seemed worth it. There was a pretty strong gradient in the subs but I found a new siril script that seems to do a good job knocking down gradients. Probably a few weeks ago at the last new moon would have been better but i’ll take this for now. The blotch at around 2 o’clock is dust that wasn’t mitigated by my flats. Besides the script I would have used siril’s auto-stretch histogram, the asinh function to raise the blackpoint and colour saturation to boost the colour.

I’ve been looking lately at all-in-one astrophotography solutions like stellina or the EVscope. It’s not that i can’t get decent results but it’s a lot of hacking around in the field and after the fact.

Grainy M51 Short Shot

This is M51 and NGC5195. It’s grainy because it’s only 8 shots. 75 second exposures at ISO 800 through the William Optics z61 so 360mm, f/5.

I’ve cropped it to be similar in size to a shot i did through the takumar lens around this time last year. The Takumar shot (below) is a single exposure because i hadn’t discovered siril yet.

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.

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 https://www.youtube.com/watch?v=tuzQL_1xe7c):
-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