Astrophotography with the SIGMA fp – I have always been fascinated by the night sky. In particular, the huge variety of Nebula and other Deep-Sky-Objects and the structures they contain. As such I have always had as a dream that one day, perhaps, I would be able to work with images of these objects myself. The launch of the SIGMA fp I took as the starting point for the journey to realise that dream.
Why the SIGMA fp ? This camera was designed as a stills and professional video camera. In order to be able to take video for several hours without overheating the camera has a heatsink built into it. This can be seen on the sides of the camera. This means that the camera is able to control digital noise extremely well. There is one other type of photography where this is absolutely critical and that is astro-photography. Faint Deep-Sky-Objects need very long exposure times at relatively high ISO values (most often around 1600 being a good compromise) and thus the control of digital noise is a fundamental factor towards producing a good image. The “sweet-spot” for the SIGMA fp is ISO 1250.
My choice of telescope is the Celestron RASA 11” V2 (620mm, F2.2). Primarily driven by the desire to have as small an F-Stop as possible for the best possible light gathering properties. In the configuration of this telescope the camera sits in front of the glass (see image), which means that it is imperative that the camera is as small as possible. The SIGMA fp is the smallest full frame camera in the world – a perfect match.
As a tracker I have a 10Micron GM1000 HPS. This needs a model of the sky to be built by going to ca. 20 bright stars in turn and aligning these exactly. I have used the IOS 6 setting on the camera to block the light of all but the brightest stars making the model building significantly easier (plus 8x zoom in the camera live-view plus 9x zoom in the field monitor – HDMI feed).
Its been a steep learning curve 😉 … From the first outings under an 85% moon (Rosetta/Orion/Horsehead Nebulas) and hard, high humidity frosts (Think – “The Day after Tomorrow” 😀 …) to every set-up and focussing error I can think of (and several I didn’t) … Focus is achieved using SharpCap, which takes the camera live-view feed after feeding through a field monitor, which is how I do most of my macro work, via a video capture card and the Celestron USB Focus-motor. This is probably the most difficult task and something that would be almost impossible to achieve without the focus motor and computational interpretation of the diameters of the stars. At 02:00 in the morning, sub zero temperatures, and already 6-8 hours “on the job”, keeping the mental discipline to get the focus right is not easy.
Since there are no “green” Deep-Sky-Objects, the green pixels (50% of all available pixels) in a full colour camera are very under utilised. The SIGMA fp I have, has thus been de-bayered (very many thanks to Daniel @ monochromeimaging.com). That means the blue/green/red sensor mask has been removed so that all the pixels can see all the colours (producing a monotone image). It now only has a glass screen that lets everything from UV to IR and have had a lot of fun using this as a terrestrial monochrome camera (some example shots HERE). Since I live in an area with relatively high levels of light pollution (Milky Way is rarely, if ever, visible to any extent), I need to work with “narrowband” filters. The images from these different filters are recombined to produce the full colour image. These narrowband filters are specifically tuned to only let through a single emission line: Hydrogen (H-alpha = 656nm), Sulfur (S-II = 672nm) and Oxygen (O-III = 501nm) so that much of the light pollution can be subdued.
It has been a very interesting experience chasing the most boring landscapes and skies that I can imagine: Totally flat and no “red cloud” sunsets – A different kind of “Big Sky” 😀 (Even if I don’t want to shoot an object when it is low in the sky, the bigger the view the more stars that are available to build the tracking model).
Everybody remember’s their “First-Time”: Well, I can tell you, after over 2 years of planning and research (and 9 months waiting for the GM1000), the first time I pointed the scope at “IC 434”, triggered the shutter for 30 seconds and saw on the field monitor the unmistakeable silhouette of the Horse’s Head appear (1240mm via the SIGMA TC2011 2x converter) – “YES!” – It was a pretty big smile! The data are not as good as they could be (85% Moon); the focus and/or seeing perhaps not quite as I would like; but I didn’t care – That is the moment and shot, I’ll always remember, and, I will be as proud of this shot as any other that I will ever take …
Its been an interesting few weeks and I have have really enjoyed the start of the journey! The SIGMA fp in combination with the Celestron RASA 11″ and the 10Micron GM1000 HPS has shown that it can produce the results I was hoping for … I am very much looking forward to the next New Moon 🙂