Testing A New Widefield Setup
Since moving to CCD imaging a few years ago, one thing I’ve missed is the wide field provided by the large chip on a DSLR. This coupled with the ease of imaging with basically any lens (within reason – some are better than others for astro work), is something I’ve missed. This has been offset my the huge advantage that mono imaging has brought – mostly around narrowband work.
A good friend in my astro society has been using an adapter to attach canon EOS EF lenses to his ATIK CCD for a while now, which allows combination of the mono capabilities and high sensitivity of the Atik CCD Chip, and the wider field provided by the much shorter focal lengths of the multitude of lenses available. With an additional EOS adapter, other mount lenses can also be used (e.g. Pentax, M42, etc). As astro imaging doesn’t make use of the autofocus etc capabilities, then you can pick up manual lenses dirt cheap on eBay. It has a natty extendable lens hood that kept dew off during first light, which was a bonus
I decided to take the plunge with a Sigma 135mm f3.5 lens – a manual prime I picked up on eBay for the princely sum of £22 including the postage. This is a decent prime with tried and tested results for astro work. Stop it down a click or two and it produces a very respectable image. This was coupled to the Atik 314L by the use of what appears to be a clone of the Geoptik EOS adapter that’s identical, save for the snazzy orange finish. The adapter also has a 1.25″ filter thread between the lens and the CCD, to allow the normal narrowband, colour, or Lum filters to be used.
I already had a nice sturdy Astro Engineering side-by-side bar, with the other side being used to hold an Altair 10×60 finder-guider, with a helical focuser holding my SX Lodestar guide cam. The overall balance between the guidescope and the imaging side was pretty close, and a little sliding back and forth in the Vixen shoes resulted in a nice well-balanced setup.
I set up SGP for this new equipment profile (removing the auto-focuser and the USB filter-wheel, as well as changing the image scale etc). I was gobsmacked when it plate solved first time (even when I left a Bahtinov mask on that I was trying to use to focus!). I focused as best I could (remember this wasn’t supposed to be an actual imaging run – more a test) and then calibrated the finder guider in PHD. Finally I set an Ha imaging run going on the Veil complex in Cygnus. The ease of guiding such a wide setup wasn’t lost on me – it was lovely to have a nice flat guide graph, and know that there would need to be one heck of an issue with guiding before I noticed any star eggyness in an expansive field of view like this. I tried both 5-min and 10-min subs with no issues whatsoever (save the odd plane flying through). Unfortunately, the conditions weren’t kind that night – the sky wasn’t very transparent, with lots of high cloud. This resulted in quite a light-pollution gradient, but I managed to process most of it out. In the end I captured 1hr 40min of data, all of which was usable. The fruits of this are below…
This wasn’t bad at all considering the conditions that night, and bodes well going forward. I’m looking forward to capturing some of the bigger stuff that’s eluded me in recent years…