Well, plenty of interest in this little blog and its pictures, thanks for all the hits and feedback over in Faecesbook land, Flickr and Google Plus!
Since the last post you may have noticed that I had time to reprocess the two key images, featured here.
An astro-colleague over here, ‘Alistair’, kindly suggested to me that I needed to further process the image, particularly in relation to removing any background gradients due to faint light pollution, as well as various contrast and saturation tweaks. Thanks maaate!
It turns out that Pixinsight’s Dynamic Background Removal tool is incredibly powerful and effective. As you see, applying the tool stripped the images of any confusing background, revealing an amazing quantity of dust and details! That was the main change to the images, although I later used Lightroom’s various development tools to further enhance the images. After a very careful complete Pixinsight processing.
So with these 2 images, I am officially astounded by the abilities of the new Sony A7s. Just incredible, I am one very happy customer of JTW Astronomy! Even better, I am perfectly satisfied with the scope/camera combination, its field of view is perfect for the wide vistas I like to capture at this stage of my astro-adventure. Furthermore, the feared issue of low resolution/under-sampling appears non-existent to me, the general size and shape of small stars is most pleasing.
Noise at ISO3200 appears more than manageable. occasionally I spot the odd hot pixel, requiring a minor edit in Photoshop, but it’s nothing alarming IMHO. And I’ve discovered that Lightroom’s noise control routines are very, very good. So this puppy is really settling down into a Pixinsight/Lightroom workflow that is proving to be both effective and efficient in relation to the amount of time spent editing.
Good news is that I heard that JTW should be ready to start doing the cooling mods for the camera in around 6 weeks, say around February time. Can you tell I”m excited by that prospect?!
Out of curiosity and with the fast abilities of the camera, I was able to try stacking a large variety of numbers of images, namely the LMC image. I stacked 120, 60, 30, 15 and 7 images in different but similar processes in Pixinsight.
Alas, I am disappointed to say that I couldn’t observe a difference, even a 2% difference, in the different numbers stacked! I think it has a lot to do with the relative efficiency of the camera giving a strong S/N ratio, plus the short duration of the individual subs (only 30 seconds).
Fortunately, I did a similar experiment with the Horsehead image, that used 2 minute subs. Below is a series of images, in JPEG format (so at finer levels of comparison, the differences are disguised/reduced to an extent).
To me, the images PROVE that stacking 30 shots is well worthwhile, certainly above 10! The jury is out in relation to 20 versus 30 however, the difference is very subtle. The main differences are in reduced levels of noise, logically.
The below images are, in order, sets of 3, 10, 20 and 30 stacks of 30 second subs. I can see an improvement in 30 versus 20, however this is only at an extremely zoomed in level. Many may opt, like me, to go for 20 when time is valuable:
My darling wifey has allowed me yet another trip to the country this weekend! She is turning out to be very supportive, quite a surprise. Maybe she is seeing a lover on the side?! I don’t care…
After the clear success of two-minute subs, on Saturday evening I will try 4 minute subs. I have used Pixinsight’s optimum exposure calculator to work out the maximum efficient exposure up in Heathcote – it recommends only 4 minutes at ISO 3200! Not bad for a dark sky site. At 4 minutes, the histogram will be well in the middle I suspect.
I am salivating at the prospect at imaging both the Pleiades and the Rosette Nebula with this setup. As a bonus, my Astronomik 12nm, 2 inch Hydrogen Alpha filter arrived this week, meaning that I can thoroughly test the narrowband performance of the camera. I will be trying exposures at 3200 and 6400 to see how quickly I can get the Ha data. Seriously tempted to redo the Horsehead with the filter as well.
So wish me luck and stay in touch all of you. I’m always interested in feedback or ideas, indeed challenges to whatever I say.