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Sunday, June 07, 2015


One of the things I enjoyed doing with my roommate's telescope was astrophotography - that is, taking pictures of stars, planets and nebulae.  I only tried it a few times, and there was definitely room for improvement but still have a few prints of the better shots.

There are a number of reasons that my images didn't turn out very well.  Processing wasn't what it could have been.  I didn't guide the scope perfectly.  The film wasn't optimized for that.  I was a beginner.  It took a week to get feedback on the images, and I wasn't taking notes.  Worse, I had an electronic camera that rapidly used up the (very expensive) battery while the shutter was open during long exposures.

One thing you will quickly learn if you get a shiny new telescope (even a very good one), is that you won't be seeing a lot of color.  Brighter stars have decent color variety, but nebulae are just white puffs of smoke or clusters of similar colored stars.  That's why I wanted to try my hand at astrophotography - because I couldn't see what was in all the textbooks.

Film (and now CCD cameras) are wonderful, because if you give them enough time for light to accumulate, they will show even faint images in full Kodachrome glory.  If I were to attempt the same thing right now, I'd probably manage to have pretty good images right away, by using a CCD camera, laptop, and color enhancement.

There are a couple of ways to go about astrophotography.  The first is the easiest, and it's called "Piggyback" photography.  You mount a camera on the body of the telescope, and use the main telescope clock drive keep the camera pointed at the desired object, and make small manual corrections to correct for minor drift.  Because the telescope usually has higher magnification than the camera, the camera should not experience image drift.

Below is a picture of a piggyback arrangement.

The other technique is called prime focus photography, and this is quite a bit more difficult.  Your camera attaches directly to the telescope, and it becomes the camera's lens.  Guiding is trickier because an SLR camera won't show you an image with your shutter open.   I had no luck with this...

Below is a setup for prime focus photography.  The adapter between the telescope and the camera has what is called an "off-axis guider".  This allows the photographer to make ensure the image remains centered.

I no longer have access to is a high-end telescope with an equatorial mount.  However there is a cheap work-around for guys like me:  The Barn-Door hinge tracking mount.  Check this out!  If you point the hinge axis toward Polaris, and run the stepper motor, the mount will counter the earth's rotation and you will be able to get the shot!

 I think it would be a fun project, even if I don't really have the time or the great seeing for astrophotography.

For an article detailing the immense difficulty of getting a great time-exposure (even with today's technology) here is an interesting read.

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