Saturday, November 6, 2010

From the backyard

As with most other "hobbies", true practitioners spend lots of time, money and personal angst plying their art. Astrophotography, for me, is one HUGE time and money sink. I started out small- film and a crappy Sears telescope when I was 11 years old. Now - a Takahashi equatorial mount and astrographic telescope, high-end digital SLR cameras, laptops, computers to process all the dang images . . . All for a measly $70,000 over the past 30 years.

And this is truly peanuts compared to what you can put out for high-end equipment to practice this very demanding art. Up until last night, photographing deepsky celestial targets had been a hit and miss proposition for me and my equipment. My mount, though capable, had some serious issues with tracking. Periodic error in the gear train and mechanical flexures tended to ruin 100% of exposures over 4 minutes in length and nearly 50% of exposures shorter than 2 minutes. Needless to say the frustration and throughput of my photography was intolerable.

So - last night I finally broke down and bought an autoguider. An autoguider is a seperate camera attached to the same or co-mounted telescope on the same mount as your primary imaging telescope. The autoguider takes short (usually less the a few second long) exposures of the starfield the mount is tracking and, by examining the position of a pre-designated star, makes corrections to the mount tracking to keep the stars from being trailed by drive inaccuracies, flexure of the mount, wind buffeting and the like.

A picture of my new setup is shown below - the autoguider is attached to the small telescope "on top" of the larger one.

With my setup - a laptop is used to interface to the autoguider camera and to the telescope to "close the loop" and effect the "autoguiding." Last night I tried it for the first time - from my light-polluted backyard here in Tucson Arizona. I would point the telescope at my selected photographic target, select a guidestar from the displayed images from the autoguider on the laptop - push the autoguide button, star the main imager exposure sequencing - and walk away. An hour (or two) later I would come back to collect the perfectly tracked images from the primary camera. After some experimentation - exposures as long as 10 minutes showed nosigns of tracking issues. (Longer exposures could have been tried but light pollution prohibits exposures in excess of this before serious fogging occurs.)

Below are two of my targets from last night. Messier 42 (the Orion Nebula) and Comet Hartley 2. Both images are the sum of 15 four minute single images, coadded together to create an effective 1 hour long single exposure. A Canon EOS 5D MarkII camera @ ISO 800 was used as the primary imager along with a Light Pollution Rejection filter.