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Setting up an Equatorial Mount

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Lots of folk ask about this so here's my version of how to go about it:

Typical Equatorial Mount, in this case an EQ5. It is on a pier rather than the supplied tripod but that makes no difference to how it is set up and used.


Below are a couple of diagrams showing the axiis and the axis clamps:

post-4502-0-98575100-1365436604_thumb.jp post-4502-0-72824700-1365436617_thumb.jp post-4502-0-74059900-1365436955_thumb.jp

To align the mount you set up the tripod and mount so that it is pointing North:


In the picture North is just to the left of the corner of the house - I can just about see polaris from this position! Don't worry that the mount is skew on the base plate - it doesn't matter at all.

If you are using a tripod the leg marked "N" or "North" will be pointing away from you ie that leg points North.

Set the scope onto the mount - this is the "Home" position:


The scope is pointing at polaris and is set to point upwards at an angle equal to my latitude. The Altitude adjustment bolts are used for this - loosen the North one and screw in the South one to increase the altitude (oppsite to decrease it). If the scope is not pointing due North then the Azimuth bolts can be used for fine adjustment in this direction.

For visual work you only need to be "near enough" - sight along the scope tube and if Polaris is in your line of sight then you are OK (Screams from the imagers here who have to have perfect polar alignment!!).

Now you have to point the scope at an object you want to look at and this is where the confusion normally starts. I have made a little stop-motion movie that shows how you could move the scope to view an object in the South, for example The Moon or a planet. The movie first shows the scope being moved by releasing the declination axis only until it is at 90° to the "Home" position. It ends up pointing at the observers Eastern horizon.

The movie pauses here for a second or two and the scope then starts to track across the sky by the rotation of the Polar axis only. It is this movement that is often controlled by a motor drive - allowing the scope to move at a rate that follows precisely the rotation of the Earth - thus keeping your chosen object within the field of view. It continues to track until it can go no further or it would hit the mount or pier!

post-4502-0-60985500-1365437576_thumb.gi Click to animate.

So - What happens then? The dreaded "Meridian Flip" is needed. No need to fear as this is very simple. Release the polar axis lock and gently swing the scope until the tube is horizontal. Lock it. Undo the Declination axis lock and "Flip" the scope tube through 180°, lock the Dec axis (This is a bit sudden in the movie!!!). Release the polar axis lock again and swing the scope until you find your object again, Lock the axis.

post-4502-0-10008800-1365437815_thumb.gi Click to animate.

Hopefully this helps a bit! If there is any demand I can make up a few more (or more detailed) movies to show how things work.

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That's really useful, Roger, I was thinking just the other day about something like this but for all the software that typically gets hooked up to a GEM for imaging etc.

Last year I struggled as I tried to work out the relationships between all the modules and between the modules and the hardware. Thanks to the great support on SGL I eventually I got things working but would have preferred something to refer to for those asking questions and those answering them.

I was considering putting together a flow type chart/diagram showing the many hardware and software modules and how they interrelate.

I don't have enough detailed knowledge to do this yet and get it right but would like to have go, do you think a collaborative approach would work?

Edited by nightvision

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There are quite a few (actually a lot) of different configurations that you can have, especially with computer control of the mount. The basic handset for dual axis drive, goto and then the systems like EQMOD, to name but a few! Maybe some basic tutorials would be useful for these - for this one i wanted to keep to the basic EQ type mount as that one seems to generate the most beginners questions on the forum.

I already have a few ideas for improving this one and one or two additions I could usefully make to the somewhat limited information already posted.

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A couple of definitions for you, now you know how the mount works!

Declination axis movement:

This axis is only moved to set the scope to the correct declination ("latitude") of your chosen target. In the "home" position the axis is said to be pointing to +90° and will point roughly at Polaris, the Pole star. If you unlock the dec axis and turn the scope through 90° (either way - it doesn't matter) the scope will be pointing to 0° (zero degrees) or the celestial equator. You can set the scope to any Declination angle from 90°N to about 38°South from the UK. The first minimovie show movement in Declination - the scope ends up at 0°. Once set for your target the axis can be locked and should not need adjustment while observing your target (in reality you will need tiny adjustments unless your mount is perfectly Polar aligned).

post-4502-0-57265400-1365453792_thumb.gi Click to animate.

Polar axis movement:

To follow your target across the sky the mount is slowly turned (or motor driven) around the polar axis. It is driven from East to West to follow the path of any astronomical object across the sky. To find an object in the East you operate the mount as shown in these two little minimovies. this will allow you to follow that object until it is somewhat passed due South. then you will have to perform a "Meridian Flip" (as seen above) in order to continue tracking your target.

post-4502-0-62165500-1365454011_thumb.gi Click to Animate

The polar axis must be locked to track an object but it will have either a slow motion drive, for tracking manually, or a motor drive for automatic tracking. You do not operate an EQ type mount (apart from finding your target) with the axiis unlocked.

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Thanks a lot. I've been struggling with this and so I cant wait to try this out. Hope I get it sussed!

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Just the refresher i needed after many years away from my scope, not that i had mastered it well before it was stored away.

With the impending winter i'll dig it out and make sure it's all there :/

Thanks for the guide,


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