This is far from perfect, my Sii and Oiii subs all used automatic dark subtraction, but used the wrong darks…
Author Archives: Neil Wyatt
This is the result of last night’s ‘learning session’, thanks to Rob (who has a very nice little observatory!) for hosting.
Stack of the best 12 images, also using flats generated with Rob’s portable Flat-O-Matic which I think is going to be copied quite soon!
Here’s a version using the Ha layer as L on top of an old RGB one:
Last night I braved the cold and tackled three more nebulas for my collection 🙂
I’m sure everyone at Rosliston last night will agree it was a really good evening. It was pretty cold, despite the sky being ‘full of flame’ 🙂
I imaged two targets with my 450D and ED 66. I used the L-Enhance filter again which does a great job of controlling stars while letting emission nebulas shine. Unfortunately it does mute reflection nebula, so it isn’t a one-size-fits all filter.
Here we go – the Flaming Star and Tadpole nebulas, unfortunately the tadpoles are almost invisible:
And the Flame and Horsehead Nebulas.
I started off with my ASI120MC, and started packing up after getting plenty of video, but changed my mind after looking at the satellite images of cloud.
It did indeed clear up and I got plenty of DSLR images of the transit after less optimistic souls fled in the face of the rain and cloud! Those who stayed on saw Mercury on the preview screen and we also got stunning views through Andy’s Daystar Quark.
I couldn’t get anything usable out of Registax or Autostakkert so I manually stacked the ten highest scoring images (and added a bit of colour, to make the image easier on the eye):
Totally gratuitous, perhaps, but Rob’s description of a night observing at Castlerigg reminded me of a sunrise I saw there in the 1980s on a backpacking holiday with my brother; I got a couple of nice pics, some of my favourites ever. It was hard not to imagine our ancestors standing in the same place watching the sun over the stones.
If anyone recalls seeing ‘Children of the Stones’ as a youngster the whole series is on You Tube, it gets quite astronomical near the end although the physics is a bit dodgy! Starring the much missed Gareth Thomas, who played Roj Blake in Blake’s Seven (another astro-related point to justify this post!)
Inspired by Geoff’s results I tried using the automerge in photoshop on my pictures of the Heart and Soul Nebulas. Oddly it only matched them if I selected the Soul first! Unfortunately it doesn’t rotate the images and my two sessions were at quite different angles for some reason.
I have combined images in photoshop before, but only on top of each other, never as a mosaic, but i decided to follow a similar path:
First I doubled the canvas size for the Soul image an imported the Heart as a layer on top.
I set opacity (opposite of transparency) of the heart image to 50%, and guided by stellarium to find the rough alignment it was easy to find a small asterism on both images. Zoomed in, I overlapped one of the stars in the asterism as accurately as I could. Circles of smeared stars around this point gave an idea of how much rotation would be needed.
using the select tool I then moved the centre marker of the Heart image over the centre of the aligned star and went to the edit menu to select ‘free transform’. This opens boxes where you can alter things like horizontal and vertical size and skew the image – not needed for images at the same scale. Instead I just used the ‘rotate’ box – this lest you enter angles in increments of +/- 0.05 degrees. This may sound a quite big step, but actually I’ve found it is small enough to align stars across a whole image. It’s easiest to step in whole degrees, then tenths of a degree and finish by using 0.05 degree to get the best possible result. It’s very obvious when you are aligned as the overlapping area suddenly looks much sharper.
I then changed to the magnifying glass tool – this brings up a box asking you if you want to apply the transformation – click yes if you are happy!
I then restored the Heart image to 100% opacity. It was clear it was less contrasty and a bit paler background. I used the ‘levels’ dialogue to alter gamma and black point until it looked a closer match to the Soul – you could also do this with curves. the whole thing might have been better if I had originally process the two images the same way.
Once they matched there was still an area of overlap with poor quality in the corner of the Heart image. I used the lasso tool with a feathered edge to remove most of this corner. A small patch still appeared too pale, so I lassoed it and changed its levels to match better.
This is the result, not perfect but not bad either:
Got both of these last night. The L-enhance gives more stars than a Ha filter, but seems to require a lot less stretching to get results. Not a lot of SII/Hb in these, especially the soul.
I think these might work well as luminance layers over an RGB image. Looking forwards to using them on the Rosette and M45.
These are two images from last night, both 5-minute subs using my cooled 450D with the 130P-DS and a 7nmn Ha filter. They have been stretched in FITS Liberator and very lightly adjusted in photoshop, and some very gentle denoising in Astra Image. This is because they subs were very dark so I wanted to make full use of FITS Liberator’s ability to stretch 32-bit data.
The wizard is 30 frames, the Crescent is 22. There’s quite visible ‘posterisation’ if you zoom right in with the faintest areas, so if it’s clear again tonight I will repeat the exact sequence with the hope of doubling my subs and doubling the range of pixel values. Very pleased with the lack of noise. Now to dig out my RGB ones and try making LRGB versions.