A Barn Door Mount for Astrophotography

A Barn Door mount is a simple contraption that compensates for earth's rotation. So your photos have Round stars NOT streaking trails.

Basically it's two pieces of wood that move at the same rate (angular velocity) as the earth but in the opposite direction so the camera (mounted on the top piece of wood) is stationary relative to the stars.

It's such a simple and elegant idea.

1.Take 2 plywood boards of12x18inch.Join the 2 boards with a hinge( see image).
2. Make a hole EXACTLY 11.4INCH AWAY FROM THE HINGE-PIVOT.
3. Fix a 1/4-(tripod plate screw size) NUT thru the hole. Seal it with super glue.
4. Pass a 3" long 1/4 bolt through the nut.
4.5 Acc to mathematics the 1/4 screw will move 1° in 4 complete turns. Earth rotates 1° in about 4mins!!So u have to turn the bolt at 1 rotation per Minute. Which is thr speed of the seconds hand in a clock.
5. To make the turning smooth use a metal piece like a Ruppee coin at the point where the Bolt pushes the board.
6. To make the rotating each n precise, stick a long plastic handle.Make a clock face for you reference.

To make a Motorised Barn Door Mount you need -

1. a Low-RPM motor. Like 5 RPM 

The closer to 1 RPM the better. But remember a little change in the input voltage and you change the "rated" RPM.

I found a 4-5 RPM AC motor from a table fan (was driving the Swing of the main fan.)

The small shining dots (pointed with the screwdriver in the third photo) are the shafts on which a gearbox lowers the RPM of this AC motor. Which I think is around 300RPM

Complete Barn Door Mount.

 

An image of Arcturus, shot using the Barn Door Mount.