Sean Esopenko

DIY: Scotch Mount

June 14, 2010

Later this week, weather permitting, I’m going to try my hand at astrophotography again. I’ve seen some awesome pictures of the Milkyway Galexy and even some nebulas from people who’ve used image stacking. I want to bring in much more colour and to do that I’ll need a serious mount for my camera.

This is a Scotch Mount and you can get the plans to build one yourself at Philip Harrington’s website. What it will (hopefully) let me do is follow the movement of the sky for each exposure.  Previously I had to keep my exposures down to 30 seconds max.  Any longer than that and the movement of the stars across the sky causes streaks in the exposure.  I need longer exposures, however, to have a chance at gathering photons from extremely distant celestial bodies.  This means I have to track the sky with my camera.

I could use a proper equatorial mount but those things start at $800 and go up to $15,000.  I’m just dabbling so I googled for a while and found that the Scotch Mount, which was first published the April 1975 issue of Sky & Telescope, should allow me to do this without spending an arm and a leg.

The scotch mount, introduced by George Haig of Glasgow (hence the scotch name) is meant to be pointed at polar north, or Polaris, the north star.  Then you crank the handle a quarter turn for every 15 seconds on your watch.  It raises the platform at (almost) the exact speed of the rotation of the earth.

So according to Calgary’s weather report, at the moment, it will be mostly sunny on Friday.  I plan on staying up until about 3am that night with a pair of binoculars and a camera, seeing what I can capture.

Update (June 16, 2010): After building the mount, I sat down and read the “Using the Scotch Mount” section.  Then when I googled other people’s scotch mounts I realized mine had a design flaw: I can’t articulate the mount itself.  I thought I would just line the hinges up with Polaris by looking along the top of the hing.  I didn’t realize you had to orientate the entire hinge so that it’s shaft lines up with polaris, as though looking down the shaft, it’s spindle would block polaris.  I figured out a temporary fix by unlocking the tripod legs and having two of them laid entirely flat and one only 1 click away from flat.  This gave it enough of an angle upwards to line it with Polaris.  Now I just have to wait for good weather…

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