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I have EQ6 (standard, so no GoTo) and I am very familiar with the use of setting circles, as this was the only way to point the telescope at faint objects it the times I started as amateur astronomer (+40y ago).
The problem with EQ6 setting circles is that they are not well designed.
First, they are too small to be of a good use, but in emergency (If you do not have GoTo function on your mount) they would be of some help.... Second, the reading is problematic, the vernier would be of a great help here (You can add that if you want, though..).
BUT the real problem is RA circle, and slewing.
Traditionally, this is supposed to be Hour angle circle. That means, one should be able to set/read the hour angle of the object, and this is the angle after culmination (passing the local meridian) of the object, expressed in time units (24 hours for a full circle or 360°). Calculation of required hour angle is simple addition, HA = ST + AR (Hour Angle, local Sideral Time, Ascensio Recta). Simply subtract 24h from result if it is bigger than 24h.
However, EQ6 hour circle is not that.... It is actually the RA circle.
You will see what I mean if you watch the mount for a couple of minutes while tracking (circle is fixed). You will notice that the setting on the circle is not changing, even if you slew. And this is not supposed to be because hour angle IS changing as the mount tracks.
Someone may argue that RA is not changing so RA circle setting should not change either. But what if you are slewing in RA direction? The circle setting remains the same, and this is not what it is supposed to be, because you ARE changing the RA when slewing.
When I will be dismantling the mount in the future (to get rid of some backlash present) I will also consider modification of this setting circle, to turn it into proper Hour Angle circle. Essentially, it needs to be locked on the other side - on the DEC axle assembly. But, on the other hand, the current design automatically performs hour angle calculation (from sideral time - which is kept by tracking motor - and RA
Another problem is that it is designed for Northern hemisphere (lower numbers, closer to lines).
For us Down Under, we should use upper numbers (they go in opposite direction)
So, to find the new object with the help of EQ6 setting circles, you point the scope to a known object (as described by Babalyon 5) and adjust the circles coordinates reading by rotating them and fixing them by screws (If the mount is properly polar aligned, DEC circle will be always OK after first setting, so you do not need to adjust it again, unless you are changing scopes).
Please note, tracking must be ON for the whole session.
Then, you can find the other objects by pushing the scope to appropriate coordinate readings, but DO NOT use slewing, as this will screw up the reference for RA. Also DO NOT switch OFF the tracking during the whole session, as this will have the same effect as slewing: RA reference will be lost. If you really have to use slewing, you will have to adjust RA circle again, on object with known coordinates.
However, if you are using GoTo, all that above is not really needed.
Last edited by bojan; 11-08-2008 at 07:43 PM.
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