“How to set the equatorial home position”? is a question I remember asking at the very start of my adventure into astrophotography. If I’m being honest, the literature back then was a bit sketchy. Dry. Not as easy as it really ought to have been. So I set about making this tutorial on how to set the equatorial home position.
In this article, I’ll be writing the instruction book I wish I could’ve found those years ago, and also there’s a video example on my YouTube channel about setting the equatorial home position. In this example, I’ll be using the Sky-Watcher EQ6-R Pro to demonstrate. But this works for any German Equatorial Mount or Chinese Equatorial mount. Harmonic mounts can also be included in some aspects but they’re a bit more advanced.
Grab your spirit level, and let’s get into this article then on how to set the equatorial home position.
Contents
- What Is The Equatorial Home Position?
- How To Set The Right Ascension Axis Home Position
- How To Set The Declination Axis Home Position
- Video Demonstration
What Is The Equatorial Home Position?
The equatorial home position, or EQ Home Position, is the classic interpretation when we think of an astrophotography mount. It has the telescope tube pointing directly forwards, into the sky. Ready to be aligned to the celestial pole of your hemisphere. The counterweight tube is also directly vertical, pointing towards the floor.
Of course, you can set any home position you want to with your mount. Most software, such as ASCOM EQMOD devices, programs like Astrophotography Tool and N.I.N.A will let you choose. Some mounts have a custom home position in them also such as the iOptron CEM70.
In that case, you set your mount to custom coordinates by using the directional controls, and then set it as a saved custom home position. This may be useful if you want to rest the telescope horizontally in order to clear a sliding roof in a roll-off-roof observatory.
However, it is commonly agreed the equatorial home position, the point of this article, is as shown above. Weights down, tube pointing forwards.
How To Set The Right Ascension Axis Home Position
The Right Ascension axis on an equatorial mount is responsible for the main tracking of the telescope. It is the one that should be moving. Guiding will make adjustments to declination, but its with right ascension which the sky appears to move to our perspective. It is in right ascension that we compensate for.
Setting right ascension accurately will help with polar alignment initially, as we have to do some sort of rotation around right ascension during the polar alignment stage. From there, having the right ascension equatorial home position set correctly will help with the go-to accuracy of the mount, before any star alignment takes place.
Step One: Set The Right Ascension To Horizontal
The first stage in setting the right ascension is to have it laying in a horizontal position. Remove all items from the mount. That means the telescope and counterweights. We want the mount to be bare.
From there, using your spirit level, you want to bring the right ascension counterweight bar up until it’s perfectly horizontal. Place your spirit level onto the bar and use the bubble to let you know when it’s perfectly horizontal.
Once the right ascension has been levelled. Lock it off with the clutch controls. We’re now ready to do the precise movements in order to set the equatorial home position in right ascension.
Step Two: Set The Right Ascension Setting Circle
Now we’ve got our bar levelled, it’s time to use the setting circle. You may never have used it up until now, and quite frankly most of them are quite inaccurate for actually finding things. However, the right ascension setting circle is perfect for setting the equatorial home position!
The right ascension setting circle is effectively a clock. It goes from 0 midnight to 23hrs 59 minutes. As all celestial coordinates are linked to this clock reading in right ascension. For our purposes however, we’re going to use it to know when we’ve turned exactly 1/4 of a rotation!
First of all, move your setting circle around until 6pm is shown to the arrow. This way, we’ve set our mount’s setting circle to 6am or 6pm, depending which scale you’re looking at. Pick a scale (top or bottom) and keep it consistent!
Now, either using the clutches or the hand controller, we need to move in right ascension.
Hand Controller: If you’re using the hand controller, set the slew rate quite high and keep the right ascension clutch tightened. Use the controller to turn in right ascension until the weight bar is pointing downwards.
Manually Moving: Release the right ascension clutch, then slowly and gently rotate the mount in right ascension until the bar is pointing dowards.
Regardless of which method you chose, the hand controller or the manual movement. We want to turn the mount until right ascension is showing either 0 midnight, or 12pm (depending which scale you’ve chose to use). The important thing is the weight bar is facing downwards.
It’s important to be smooth and careful in this step. The setting circle may slip and not turn with the mount. Also, there’s usually a thumb screw on the setting circle. Make sure that’s just tight enough to have enough grip so the circle moves with the mount!
With that done, we’ve successfully set the right ascension into its home position, and we can move onto the declination axis. Well done! We’re half way with how to set the equatorial home position.
How To Set The Declination Axis Home Position
The equatorial declination axis is responsible for north and south movements. You’ll occasionally see it written that way, particularly when looking at guiding software. Right ascension is east and west, declination is north and south. Both are important when figuring out how to set the equatorial home position.
A correctly set declination home position is critical again for point accuracy during go-to, star alignment and even plate-solving. However, if you’re using plate-solving to polar align as in the ZWO ASIAir or if you’re using software like SharpCap, having correctly set declination is vital to this form of polar alignment.
Step one: Set The Declination Position To Horizontal
Similarly when we set the equatorial home position for the right ascension axis. The first step is to undo the declination clutch and rotate it around until it’s facing horizontal.
If you’re fortunate, and most likely you will be unless you’re using an enormous spirit level. Your level will actually fit nicely into the vixen puck on the mount!
Tighten the spirit level in and begin to turn the mount. Conventionally, the puck knobs will be off to the right as you look from behind the mount.
Just like right ascension, use the central bubble if you have multiple to find the horizontal position. Once you’ve got this set, tighten the declination clutch.
Note though on some mounts, like my EQ6R-Pro, when you tighten the clutch, declination may shift over a bit. Just keep an eye for this and make any further adjustments as necessary.
Time to again use the setting circles for our precise measurements to set the declination home position.
Step Two: Set The Declination Setting Circle
The equatorial declination setting circle is often located near the puck, or near the counterweight shaft. It definitely will be located on the declination axis somewhere though. However if you’re struggling just check your user manual for the mount.
The declination setting circle operates in a circle and uses degrees ° to calculate its position. Every celestial object again has a degree setting. The declination setting circle goes from 0° to 90° and then back down.
We’re trying to find a quarter turn again. 1/4 of 360° is 90°! So we’re going to set the declination setting circle to 90° and again just watch out for the thumb screw.
Declination circles typically have more tension on them than the right ascension and aren’t as prone to slipping.
Now, either using the clutches or the hand controller, we need to move in right ascension.
Hand Controller: If you’re using the hand controller, set the slew rate quite high and keep the declination clutch tightened. Use the controller to turn in declination until the puck is pointing directly forwards.
Manually Moving: Release the declination clutch, then slowly and gently rotate the mount in right ascension until the puck is pointing directly forwards.
Once the declination has been set, we’re all done! That’s how to set the equatorial home position. Whether you have a German Equatorial Mount or Chinese Equatorial Mount. It isn’t has hard as some guides seem to make out.
Video Demonstration
If you want to see me do this for real, then you can check out my video tutorial on how to set the equatorial home position!