As I said in the project announcement, living in the UK we have a major problem to contend with trying to pursue our hobby – the weather! There are very few good clear Moonless nights to take those perfect images. I have also compounded the problem by moving from a very fast (Hyperstar) imaging system that worked at f#1.85, to a much slower refractor-based system working at only f#4.5, i.e. six times slower.
The problem I am trying to solve is how to get as much image data as possible in the short time allocated to us during the year. One way of increasing the data is to parallel up the imaging, that is, to have several identical optical imaging systems all imaging the same object at the same time.
So, for instance, if we had four identical Sky 90 plus M25C imagers all photographing the same DSO at the same time, we could get the equivalent of 12 hours worth of total exposure data as one system operating for three hours (a typical single night’s imaging time).
Next we have the question as to what basic imaging system we shall parallel up in this way. You could conceive of four Hyperstar systems, maybe even using 14″ rather than 11″ mirrors. Although possible, the large size of the imaging head would be difficult to accommodate in a glass-fibre dome, even the larger 9-foot version (I have the 7-foot diameter Pulsar Optical dome at present). Basically, use of reflectors would make the unit very heavy and unwieldy. So that moves us to refractors.
Initially I thought of using 4 Sky 90 refractors [with f#4.5 reducer/corrector] because they appeared to be the fastest, cheapest, apochromat that was readily available. However, recently the Takahashi 106 f#3.6 wide 40mm diameter focal plane (which will easily cover the big format CCD cameras) has made an appearance – this will make an ideal mini-WASP basic imager.
Unfortunately, I have already invested in 2 Sky 90 refractors, so I need to follow a different route, but for someone starting from scratch, 4 FSQ 106 refractors, with the f#3.6 reducer/corrector and a big mono camera like the Starlight Xpress H35 or H36, would create a near ideal system.
I would recommend narrowband filters on 3 of the refractors to provide effective RGB channels, with maybe a straight IDAS light pollution filter on the fourth refractor to give the luminance channel. However, with my two Sky 90s, I need to consider other alternatives…