New PA system with coffee !

[Guest peepshow]

I am devising a system to check my PA and RA speed using on old canon 350d with a 200mm lens.

This gives a FOV of approx 6 degrees equating to a 24 minute movement in RA. 

This is all mounted on a barn door tracker system BTW.

 

The camera is mounted pointing to about the celestial equator. 

With the RA  tracking motor OFF a 30 sec exposure is taken.

About 8 minutes later another 30 sec is taken.

 

The tracking motor is now switched ON.

Immediately another 30 sec is taken.  Leave the RA tracker motor running.

 

Now comes the difficult bit.........I .go indoors and have a cup of coffee for 8 minutes and get warm.

 

Then take a 4th 30 sec exposure and I then upload the four exposures into my PC.

 

Open Rot and Stack and open the four pictures in it.

Ignore the select reference but hit 'animation.'  This cycles continuously the four images one after the other. 

 

I now use the first two shots which have 30sec star trails to line up a straight edge ( a piece of straight paper) on the PC's screen on the same star in each shot to create a datum line.  Any star will be approx 2 degree in RA apart and be about 1/3rd the screen width apart one shot to the other.

 

Now when the other two images are animated on screen I can immediately see if the PA is wrong and also if the tracking speed is incorrect..

Incorrect PA will show a star from the 3rd and 4th shot not in line with the datum line and incorrect speed will show two star images instead of one on the datum.  (there are no star trails on the 3rd and 4th shots of course)

 

If a 3rd shot star is behind the 4th shot then the tracker is running slow. If in front it's running fast.

Star travel moves across the PC screen from left to right BTW

 

One can refine this system  by using different focal length lenses and timings between shots which I am now mulling over to get greater accuracy..........and more coffee breaks toooo. 

 

It's easier to do all this than describe it well, but there you go.

Edited November 17, 2013 by peepshow