A Newbie’s Adventure in Astrophotography: Part 3

So I’ve successfully taken my first Moon photograph, and was looking to go deeper.  At the time, Saturn was high in the sky and I decided to try to photograph it.  I took a few exposures and also learned something.  You can get a much better view of Saturn through the eyepiece.  As it turns out, my DSLR wasn’t the optimal camera to use to photograph planets.  Since then, an number of hardware and software advances make it more possible, but at the time, I chose to move on.

Photographing deep sky objects is nothing like Moon or even planet photography.  Deep sky photography utilizes multiple long exposure photographs.  That is while the mount continues to track a target, the camera opens the shutter and holds it open for a specified duration.  That means a lot is going on while imaging, of course the mount and camera do most of the work.  This fact will allow you to automate the most tedious aspect of the process, so most of the effort goes into the setup.

The first thing you have to do is get the camera focused.  If the Moon is up, you can focus on that.  The same with a bright planet like Jupiter or Saturn.  But your next best option is a bright star.  My camera, the  Canon XS, has live view.  Live view allows you use either the LCD screen on the camera or a laptop computer as the viewfinder.  With live view, you can zoom in on a bright star and turn the focus knob until the star appears to be a pinpoint.  This allows you to get very close to perfect focus.  That said, only the 10 or so brightest stars will be visible on the screen, so don’t expect to see what you would see through the eyepiece.  When it comes to Live view, it is a focus aid and no more in regards to deep sky photography.

A Bahtinov Mask is a handy tool for achieving perfect focus.  My focusing routine went from being a 20 minute affair to less then a minute.  It also gave  me better focus which resulted in more attractive stars.  You can download a template to make your own Bahtinov mask or purchase it at Focus-Mask.com.

My first Deep Sky photograph was of M3 a globular cluster(top right).  Globular clusters are the best targets for newbies.  They are bright, Looking back, my results weren’t terrible, but they weren’t anything to write home about.  Needless to say, I was ecstatic about my results, and was hooked.

I considered myself lucky the first few days I had the telescope.  The weather held out, and I got to use it before the clouds rolled in a couple of days later.  This is another aspect of the hobby that can sometimes be frustrating.  For visual observing, partly cloudy skies can still provide for an eventful outing.  For astrophotography, clouds are a no go.  So I found myself checking the weather and hoping for clear nights.  These days I use the Clear Sky Clock on the top of the page, and it has proven very reliably and handy.

The Telescope I use, a Celestron CPC-800 is on an Alt-Az mount.  What this means is that the telescope tracks the sky on two axis.  This is unlike an equatorial-mounted telescope which tracks the sky on a single axis revolving around the star Polaris.  For deep sky astrophotography,  an equatorial mount is optimal.  That is not to say you cannot get nice images photographing in Alt-Az, but an equatorially aligned mount will allow you to take longer exposure photographs.  The limit in Alt-Az would be around 30 seconds otherwise, images show field rotation.  This is the biggest limitation of Alt-Az mounts when it comes to astrophotography, but there is a simple solution.  An equatorial wedge allows you to equatorially align an Alt-Az fork mounted telescope like the CPC.

I purchased the Celestron HD Wedge.  Now I could push my exposures a bit further.  In Alt-Az, I was getting 20-30s exposures.  At this point, I am able to go 45s without showing any trailing stars.  My pictures are improving, but I know I still have a way to go before I’m going to be framing them.

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