New Kit, and Two (Very Different) Views of the North America Nebula
As I mentioned in my previous post, I’ve recently been revamping my entire setup. Two major parts of this were the purchase of a One Shot Colour (OSC) CMOS camera, (a Player One Ares-C Pro), and the second was the addition of a high-quality Samyang 135mm f2 lens for widefield imaging.
The purchase of the camera was mainly down to the number of decent nights that us UK residents get to gather the necessary photons. I love imaging with mono cameras, in that they are generally incredibly sensitive, and produce amazing results. The downside is that, unless you want a mono final image, you need to capture the target in at least two different wavelengths, and combine them to form a colour (or pseudo-colour) image. OSC cameras have the downside that they’re generally not as sensitive, and as a rule are noisier. However, this is offset by the fact that you can capture all wavelengths at once, and still have a lot of latitude for the way you process, and the colour mix of the end result.
The Player One Ares-C Pro, is a reasonably new entrant to the relatively crowded astronomical CMOS camera market, and indeed, Player One themselves are new kids on the block overall, and have only been producing cooled cameras since 2021. The Ares-C itself features a Sony IMX533 1” square format monochrome sensor. This 1″ diagonal, 3.76um pixel slab of loveliness is a very low noise chip, used in various other cameras, including the well-regarded, and widely used ZWO ASI533MC. The chip itself is very clean (i.e. very few hot and cold pixels), and produces remarkably low noise images. But the best thing is that it doesn’t suffer from ‘Amp Glow’, which is an artefact that you get on many CMOS-based cameras that results in a hot spot on one side of the image, generally with starbursts the radiate out from it. This has to be ‘calibrated’ out by the use of dark frames, and even then, is not always possible to get rid of entirely, as on certain cameras it’s so bright that it drowns out the actual signal from the subject you’re imaging.
In contrast, the Ares-C Pro (and other IMX533-based imaging cameras), has zero amp glow. In fact (and this is one thing that really attracted me to it), if you keep you imaging train free of dust bunnies, and don’t suffer from major vignetting, you can actually get away with no calibration frames at all. That’s right NONE! I know that some will call this heresy. “Adam, how can you possibly be promoting NOT using calibration frames of any type! Are you off your rocker!?”. Well… after years of experiments doing just that, a fellow imager has come to the conclusion that as long as you keep your imaging train clean, you can indeed get away with it, with the gains being extremely marginal at best. All the images I’ve produced so far with it have used no darks, flats or bias frames, and look absolutely fine to me.
So, after a bit of a leap of faith, me and a few astro-imaging buddies took the plunge and all acquired Ares-Cs at the same time. I’ve tried it with three different setups – my Altiar Starwave 102ED f/7 doublet, by Meade LX90 ACF with f6.3 reducer, and a new acquisition, my Samyang 135mm f/2 ED UMC manual-focus prime lens.
This post shows two images of the same area – one taken with the Altair 120ED, and one with the wise-field view of the Samyang 135mm lens. This is an extremely well regarded lens that is one of the best available for astro-imaging, producing better results than some far more expensive astro-centric optics. Most camera lenses are ill-suited to astro imaging as, although they may be pin sharp for conventional photography, if you throw thousands of tiny pinpoints of light at them, then the colours are generally a bit all over the place on the stars (chromatic aberration), and the corners of the image are often distorted (i.e. the ‘field’ isn’t flat). Not so with the Samyang. It’s got one of the flattest and best colour-corrected images of any comparable lens.
So on to the images. The first is a close-up of the ‘Cygnus Wall’ area of the North America Nebula (the ‘Gulf of Mexico’ if you will). The second is a wide field image of the area. The third shows where the first appears not he second, illustrating the difference in field-of-view between the Altair 102ED and the Samyang 135mm lens.
The Samyang offers some lovely bonuses:-
- It’s FAST! At f/2 it has a very large aperture for gathering photons. It’s basically around 8.5 (or so) times faster at gathering the light than the Altair 102ED.
- It has a very wide field. Coupled with the Ares-C, it gives a field of view of approximately 5 degrees. That’s 10 times the width of the full moon!
- It’s VERY well colour-corrected. In fact, it’s actually better corrected than my telescopes.
You’ll notice the difference in the colours of the images. This isn’t down to the optics used, but the. post-processing involved. The widefield shot is probably closer to the ‘real’ colours, but the close-up is processed to more strikingly show the differences in the Hydrogen Alpha and OIII wavelengths. In each case it was purely an aesthetic choice on my part.
The Samyang has another advantage in that the whole setup can be put on an HEQ5, side-by-side with an Altair 60mm finder-guider. This makes guiding extremely easy – I had the flattest guide graph I’ve ever had in my entire life!
The whole setup itself is also extremely portable. Portability and ease of setup has always been one of my main concerns. This is especially the case now I’m using an EQ6 Pro for my main imaging rig. Originally, I’d been intending on selling the HEQ5, but this side-by-side setup has given it a new lease of life. I can leave the side-by-side mounted on the HEQ5 and just transfer the camera and mini-PC (more on that in a later post!) across when the need arises.
The whole lot can then be grabbed and plonked down in the garden very easily. It also goes really easily in the car for a quick trip to slightly darker skies – something I’ll now be far more likely to do than I have been previously. Darker skies are a massive advantage for any imaging, but for widefield even more so, as light pollution is far more likely to create gradients on wider shots. Also, a fast lens like this lends itself to going after very faint nebulosity, and in those cases, darker skies are a must.
One thing I’ve also started doing recently, as part of my image processing workflow, is extracting the stars from images, to allow processing of the nebula without having to worry about making the stars all screwy. Many images require the use of processing steps that would otherwise mess up the stars. Sharpening, noise reduction, levels, curves etc, can all affect stars in an adverse way, and so you need to finds a way to ‘protect’ the stars by either using masks or some other method. Using a small pice of software called ‘StarNet2’ you can actually move the stars into a separate image, and replace them afterwards, once your processing is complete. It makes an amazing difference to how straightforward it is to process the nebula. Its also produces a starless image, which, in itself, is aesthetically really interesting. The image on the right here is a part-processed starless version of the widefield above.
So… for info, these are the details of the images in this article:-
Firstly the narrow field close-up of the wall:-
And then the widefield shot:-