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Stars tracker

by pchretien, published

Stars tracker by pchretien Sep 10, 2011

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Summary

To take pictures of the night sky you need to shoot long exposures in order to grab as much light as possible. The problem is that, because of the rotation of the earth, the stars are constantly moving in the sky. This mechanism allows you to cancel the apparent movement of stars while taking long exposures of the night sky.

The way this version has been designed, you need to turn the threaded rod once every minute. Using a 50mm lens, the stars movement will start to be visible on your picture after 20 to 30 seconds. I recommend turning the handle once every 15 seconds.

I uploaded a pictures of all the FAIL parts I printed for this project. I love development by prototyping!

Instructions

This still is a work in progress. I'll post the source files, a video and more detailed instructions later ...

1 - Print all 5 stl files
2 - Press fit a 1/4" nut in the bottom of the hinge6.stl part
3 - Press fit two 608 ball bearings in the hinge6.stl part
4 - Insert the 1" long 3/8" bolt in the hinge5.stl part
5 - Insert the alignment scope tube in the hinge5.stl part
6 - Press fit two 608 ball bearings in the hinge5.stl part
7 - Attach the wheel to one end of the 1/4" filted rod using two 1/4" nuts and the butterfly 1/4" nut
8 - Screw the cylindrical lock screw on the 1/4" threaded rod
9 - Screw the ball of the ball joint to the other end of the 1/4" filted rod
10 - Screw hinge6.stl and headdown.stl to the 12" long 3/8" filted rod. There must be 11.5" between the center of the bearing and the center of the slot where the cylindrical lock nut will be inserted.
11 - Screw hinge5.stl and the ball join head to the 13" long 3/8" filted rod. Make sure there is 11.5" between the center of the bearing and the center of the ball join hole.
12 - Insert the 1/4" rod assembly into the headdown.stl piece. The cylindrical lock nut should snap in place.
13 - Attach both 3/8" assemblies together using the M6x8 shoulder bold.
14 - Snap the ball join head on the ball join ball.

To start shooting follow these instructions:
1 - Attach a camera tripod heat to the stars tracker using the 1" long 3/8" bolt.
2 - Mount the stars tracker on a tripod using the 1/4 nut on the bottom of the hinge5.stl part
3 - Ajust the tripod so that the celestial north pole appear in the center of the alignment scope tube.
4 - Point your camera to your subject and start the exposition.
5 - Turn the wheel 1/4 turn clock wise every 15 seconds until the end of the exposure.

I suggest starting with 2 minutes exposures at more than 800 ASA.

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How do you calculate when and much you have to turn the wheel, depending on the focal length?

I've ordered my first arduino - would love to build this, then connect an arduino for motorized control to compensate for the varying geometry for longer exposures!!
Any sample images with image meta/specs you can share?

I made a similar device it's called a barn door tracker, I used a 1 rpm drive to turn it. You can only get about 12 minutes out of it because of the geometry. the drive was a tamiya 156:1 gearbox turned by a servo on 3v, it was slow enough to give me 1 rpm.

hey, i've made something for a friend, to motorize his star tracker, i't in my collections.

So where is the proff?!

can we see your photography results?

Just had a look at the blog, nice work!

I'm looking at moving this way after doing some star streak photo's. I've done a stack of 100 x 30 sec ones so far.

This is taking it to the next level. I see a stepper mount and Arduino in the future!

I have not tested this one yet. I invite you to visit my blog at the following address to see a picture I took using a previous version of the stars tracker. I'll post a picture here as soon as I get one. http://basbrun.com/2009/08/03/first-light/http://basbrun.com/2009/08/03/...

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