In my last post I was at the point of deciding which refractors and CCD cameras to use. I think I’ve now solved that dilemma!
Having gone through many combinations and permutations I am thinking the best solution for me is as follows:
- Use the 2 Sky 90s with M25C cameras that I already have to give 2x the imaging field of a single Sky 90/M25C, this works out at around 4.44 x 3.33 degrees.
- Use the third slot in the supporting framework to take a Takahashi FSQ 106 working at f#3.6 and large format mono camera with a filter-wheel. The field of view of the 106/H35/H36 is actually larger than the two combined Sky 90/M25Cs, so data taken with the FSQ can be overlaid on the Sky 90 data. In the FSQ 106 optical train including a filter-wheel allows the additional data to be taken as lum [with an IDAS filter], H-alpha, H-beta, OIII, or SII this gives great flexibility in the type of data taken in this extra channel.
- The fourth slot in the supporting framework will then take the guide scope, which at the moment is a WO 80mm refractor.
This mini-WASP unit will give me twice as much data on a 4.44 x 3.33 degree field of view as either the FSQ on its own, or the 2 Sky 90s together. In other words, I can get an effective 6 hour total exposure for my typical 3 hour nightly imaging session on a massive 4.44 x 3.33 degree field with a sampling of 4 arcseconds per pixel.
Now, if at all possible, I really like to take around 100 sub-exposures for an image to ensure a low-noise, glassy smooth, final picture. If each sub-exposure is around 7 minutes, then the 100 subs will cost me around 12 hours, which is around 2 imaging nights with my FSQ106/Sky 90 system – that’s not too bad.
It would be better if I could get ALL the data I needed in a single night, and I suppose I could if I dropped the sub-exposure time to something closer to three and a half minutes, but subs in this region are only useful on star clusters, or star fields, or very bright objects like M42. For most of the faint DSOs I like to image I need at least 7 minute exposures per sub and sometimes preferably a bit more.
The supporting framework, plus refractors, plus cameras and leads is likely to come in at around 60-70 pounds in weight, so the mount needs to be a substantial piece of kit. At present I am thinking of either the Losmandy Titan, or the Paramount ME – with the Paramount being favoured, even though it is quite a lot more expensive.
So, that is where my current thinking is. The supporting framework is currently being constructed by NTE vacuum technology who are in Poole, Dorset, U.K.
I will post images of the mini-WASP array as soon as there are any further developments.
Until then, clear skies!
