Expert: Paul Wagner - 5/10/2008

Question
I just bought a single-axis equatorial platform for my 14.5" Antares dob through Astro-Mart. I appears to be good quality and in good condition. BUT...It's an ET brand, not EP - and the co. is out of business (so no website). My problem is it has no manual, as the seller told me. I'm hoping you can help me get it set up for my latitude and aligned with North, etc. Any help will be greatly appreciated, as I'm very new at this. Thank you.

Answer
Hi Tom

I don't have one of these, but the theory is pretty simple.  You need to point it due North ( not magnetic, North, but true North) and that's pretty easy--just take it outside at night and find Polaris--if you can get within a couple of degrees, you will be pretty close.  

And you need to set it up for your latitude---but that depends on the platform.  The seller should have told you what latitude the platform was made for...you can usually adjust that by a few degrees, but not ten.  It's a basic trig function to figure that out, but if you know what latitude the platform was designed for, then you can shim up the North or South end to get closer to your latitude.  

Here is a quick outline on collimating the platform to your location:

Using the platform.

The platform is ready to use now. If all activities are performed fairly accurate and the speed of the stepper motor is finetuned, the platform will follow the stars very well, if polar aligment is in order. For visual observing polar alignment is very forgiving. For optimal polar alignment I recommend using the wellknown stardrift method. Proceed as follows:

Position the platform roughly north-south, using Polaris as a reference. Assuming the platform is used at the lattitude it was made for, the platform top has to be level when positioned in the middle position.

Put a crosswire eyepiece in the focusser of the telescope and aim the telescope at a star as close as possible to the point where heaven-equator and meridian meet. The cross in the eyepiece has to be positioned horizontal-vertical.

Movement of the star in horizontal direction is caused bij a non-optimal motor speed, but we will neglect this now (assuming that the star stays in the field of view). When the star travels up, the telescope points to far to the east. The northern side of the mount has to be replaced a bit in western direction. When the star travels downward, the opposite is true. Proceed untill there is no more travel up or down.

Point the telescope at a star on the equator in the eastern sky, as close as possible to the horizon. If the star travels up, the virtual polar axis points to low and the soutern side of the platform has to be lowered. If the star travels down, the opposite is true. Again, proceed untill there is no more travel up or down.

I am not being casual about this, but if you just want to get close, that's all that's needed. If you want to do astrophotography, then you really need to install this permanently somewhere, so that you can make fine adjustments over the months it will take you to get it exactly perfect.


Paul Wagner