Astrophotography: German Equatorial Mount

When I first started trying to do astrophotography,I had a simple tripod mount.  These type of mounts are called altazimuth mounts which just means they let your scope move in four simple directions.  They go up, down, left and right.  They are easy to quickly move your scope to a target like the moon, a star, or even a terrestrial target.

These altazimuth mounts have their purpose, but the trouble with astrophotography is that the Earth is spinning.  Just like the sun and moon move through our sky due to the Earth's rotation, the stars are moving too.  If you were to open the camera shutter for a long time and just let the camera expose over time you would see the stars are moving throughout the night.  Polaris, or the North Star is the one constant star in the sky that stays in the same position and the rest of the stars will rotate around it. The pictures below show what the star rotation looks like if you left the camera exposing throughout the night.

https://classconnection.s3.amazonaws.com/970/flashcards/2386970/png/untitled1358612324401.png

http://burro.case.edu/Academics/Astr306/Coords/NMSkies_StarTrails2.jpg

Photographing a moving target is much tougher than a still target.  So some genius people invented another type of mount for telescopes called the German equatorial mount or GEM.   The scope is attached to the mount and can still move, but is much more counter intuitive than with a altazimuth.  In this case the scope moves in directions that are not as simple as up, down, left, and right.  The first movement direction is called the right ascension (RA).  When the scope is pointed towards the North Pole, then the scope moves in the same direction as the stars rotating around the north star.  The other movement direction is called the declination (DEC) which lets the scope move north and south.  This system lets the scope follow the stars through the night.

http://starizona.com/acb/basics/equip_mounts_gem.aspx

The movement of this mount to find a target is much more difficult especially if your are trying to do it manually.  It is not as simple as just moving it up and to the left to get the scope pointing at the moon.  The good news is that most of the mounts have a electronic systems built into the mount called "Go To."  You just tell the mount through an attached handheld controller which object you want to look at and the mount automatically "slews" or goes to your target.  Before you can use the GoTo system you need to calibrate the mount.  The controller will ask you to chose several stars and then slew to them.  It will be a little off and you will use the controller to move the star into the center of the eyepiece.  Each time you slew to a new calibration star, the scope will be a little more exact.  By the time you line up 3-4 stars, the mount will find any target you input and after slewing to the target it be right in the center of your eyepiece.

There are a couple of downfalls to a mount like this.  First, they are heavy.  The mount itself is fairly heavy, which means the tripods are very solid and add more weight. .  The telescope must be balanced through all movements and so there are weights on one end that also add to the weight.  The mount also needs power.  You can plug it in, use a car adapter, or get a battery for it.

If you ever want to do astrophotography then this is the next item to get after a scope.   These mounts come in different sizes and brands.  The bigger the mount the more weight it can carry.  Once you start adding cameras, bigger telescopes, guide scopes, etc to the mount then your weight load goes up and the mount needs to handle that weight.  The scope moves with a motor and you should not exceed the capacity of the motor.  If you do not only do you stress the motor, but the scope will not stay as steady on your target which is a must for astrophotography.    This is always a tough decision when you get these mounts.  They can be expensive, but you don't want to go to little because once you have new and bigger scopes you can quickly outgrow the mount.  On the flip side, the bigger the mount the heavier it gets which makes transport and setup harder.

I chose a Celestron AVX as my mount. It has performed well for me.  However I am at load capacity with my scopes.  If I ever get a bigger scope than an 8 inch SCT then this mount will not be able to handle it.  I am content with the scopes I have for awhile, so I can highly recommend the AVX mount as great starter mount that should meet your needs for a long time.

Celestron AVX at load capacity with my scope and camera