Monday, 12 July 2010

Looking across our Galaxy

Carl Sagan taught me that our Galaxy is always spelled with a capital G. Here it is. I used a slightly different technique with my Canon to get this image. I have an old 135mm f/2.8 lens with a thin M42 to Canon adapter. I thought this lens was no good, but aha! I was assuming that setting the lens to infinite focus gave infinite focus, mainly because it looks to all intents like it is throught the viewfinder. However, a slight tweak to the focus ring and it gives sharper focus. Still not perfect, but at least it does focus; it could have been out the other way and never reach infinity. Anyway... I'll stop that laborious explanation and say how I enjoyed polar scope aligning and then polar aligning an Autostar mount. I then piggybacked the camera on a scope and pointed it out of the dome to the beautiful summer milky way. I worked at ISO 800 so I could get longer exposures (6 x 1' plus a 2'). I think the trick was to get flats 'in situ' as well as darks and flat darks. These were obtained by scrunching a bit of bubble wrap in front of the lens and repeating 5 blurry shots close to the same area, covering the camera for 5 seconds when cars came past. I had to stack using 'Kappa-Sigma clipping' as opposed to 'Mean' even though one of the pics was 2 min and would effectively get ignored. Is that right? ... OK. Now let's play spot the objects!