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Atlas mount dec setting circle, should it move?

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#1 telfish



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Posted 10 February 2011 - 01:42 PM

Just unpacked and set up my new Atlas and I have a question Orion's tech support can't answer.

Does the dec setting circle move during slewing? If I tighten the setting circle thumbscrews and release the dec clutch the setting circle moves with the mount. If I tighten the Dec clutch it stops moving. Is that right? The RA setting circle moves with the mount if the clutch is loose or tight.

No big deal either way really I would just like to know.



#2 Eddgie


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Posted 10 February 2011 - 02:46 PM

First, are you sure you are not confused between the DEC and RA circles?

I can't remember for that mount exactly, but here is the way it is SUPPOSED to work.

The DEC circle on most mounts CAN be moved, but it is intended that the Dec be set to 90 degrees when the mount is pointed at the NCP.

Most mounts allow you to MOVE the circle to adjust for the telescope which might not be in perfect alignement the Dec setting circle. This could be due to the rings or the saddle being slightly crooked, or who knows what. but the idea is that when the telescope is lined up so that it is pointing to the NCP, the Dec circle should be set to 90 degrees.

Many mounts allow the cricle simply to be slipped into postion against friction. Some mounts use a setscrew or thumb screw that you can loosen to make this adjustment. Align the TELESCOPE to NCP or to a target with a known declination, and then loosen the screw, move the scale until the correct declination is indicated by the pointer, and tighten the screw.

Once the motor is driving, the scale should move with the axis. As you change the pointing of the mount in declination, the circle should move so that it keeps your posiiton.

So, the circle should always move with the telescope, and the only reason there is a screw that lets you adjust the Dec circle is because you need to allow for slight mechanical mounting differences for different OTAs.

Once it is SET for a specific OTA, the Dec scale should never have to be touched again. The screw that locks it in place should be tightened and left alone.

If you use the circles manually and you change to a different OTA, the scale might be a bit off, again because of some slight mechanical misalignment of the dovetials, ring, scope combo. You would need to loosend the lock screw on the Dec scale and adjust it accordingly for that particular OTA.

If it weren't for that, in theory, the Dec circle could be permanantly locked in place.

So, except for when you actually make the adjustment by loosening the screws, the Dec scale should ALWAYS turn when you move the scope in declination wheter the clutch is locked or not.

#3 telfish



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Posted 10 February 2011 - 03:00 PM

You are right I got them back to front! I am new at this so doh!

So it's the RA setting circle that will not move with the clutch tight and will move with the clutch loose as long as the setscrews are tight.

Thanks for the response. That is how I have the DEC setting circle set and it works fine.

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