RA circle moving when making adjustments

[soldave]

Doing a tiny bit of indoor playing with my new 130M with EQ-2 mount and have noticed something which, to me, seems a little strange. When I'm making adjustments, either large or small, on the RA axis (is that the right word? Apologies if not) then the RA circle on the mount is moving along with the pointer. Hopefully my video below will explain. My very basic understanding is that the thumbscrew above the pointer holds the RA circle in place so that it doesn't move when tightened up. The problem is that the thumbscrew is as tight as I can get it, and although I can feel more friction in the RA circle, it's not stopping it rotate when the mount does.

Any ideas on how I can resolve this? Am sure it's an easy fix but my knowledge on these things is super simple right now so I'm cautious of doing something wrong.

[Cornelius Varley]

This is how the RA setting circles should work : compare this to your own mount.

When the clutch/thumbscrew is locked, the RA setting circle should always stay pointing at the same value. The mount is being adjusted by the slo-mo cable as you track an object across the sky. That object has a coordinate of RA and DEC and this will not change when tracking (using the cable or RA motor)
When the clutch/thumbscrew is released the RA circle will be free to move independent of the pointer. The mount can now be slewed freely by hand without the slo-mo cable. 

[Guest]

1 hour ago, Cornelius Varley said:

This is how the RA setting circles should work : compare this to your own mount.

When the clutch/thumbscrew is locked, the RA setting circle should always stay pointing at the same value. The mount is being adjusted by the slo-mo cable as you track an object across the sky. That object has a coordinate of RA and DEC and this will not change when tracking (using the cable or RA motor)
When the clutch/thumbscrew is released the RA circle will be free to move independent of the pointer. The mount can now be slewed freely by hand without the slo-mo cable. 

This is what the 20 year old Meade I use does...

 https://youtu.be/QqdDC3IcF5Y

[soldave]

Ahhhh I see. Sorry, I'm still a total beginner and am working out the RA and DEC numbers.

Apologies - at least you know the level of questions you may get until I get my head around these things! 

[soldave]

17 minutes ago, merlin100 said:

This is what the 20 year old Meade I use does...

 https://youtu.be/QqdDC3IcF5Y

Again, forgive my stupidity, but when you've locked the big thumbscrew (and thereby locking the clutch), the small adjustments you're making are resulting in the RA circle changing relative to the pointer. I thought Cornelius Varley said in that situation it would stay locked together.

I may just be getting confused too with the small silver screw sitting above the pointer and the larger lock knob on the other side.😕

[Cosmic Geoff]

You should not worry about it too much as the setting circles are essentially ornamental. Even if you could use them expertly, they are only adequate for aiming a very low powered widefield telescope. In the days before GoTo, workable setting circles were at least six inches in diameter, and I have seen circles of two feet diameter in Victorian observatories.

[Guest]

10 minutes ago, soldave said:

Again, forgive my stupidity, but when you've locked the big thumbscrew (and thereby locking the clutch), the small adjustments you're making are resulting in the RA circle changing relative to the pointer. I thought Cornelius Varley said in that situation it would stay locked together.

I may just be getting confused too with the small silver screw sitting above the pointer and the larger lock knob on the other side.😕

I wanted to see what mine would do.  It did something completely different to what was mentioned before...   Welcome to confused.com!😕

[johnturley]

52 minutes ago, Cosmic Geoff said:

You should not worry about it too much as the setting circles are essentially ornamental. Even if you could use them expertly, they are only adequate for aiming a very low powered widefield telescope. In the days before GoTo, workable setting circles were at least six inches in diameter, and I have seen circles of two feet diameter in Victorian observatories.

My 14in Newtonian, which was made by Astro Systems (Luton) in the 1980's, has a driven RA circle 12in in diameter, and which is marked out every 4 minutes, but I can estimate to the nearest minute (0.25 degree). When the RA motor is turned on the setting circle moves with the pointer, so the pointer points to the same mark unless the telescope is moved manually. A lot of mounts from that era with synchronous motor drives however, did  not have driven RA circles, so that the circle did not move with the pointer.

I still rely on a sidereal clock (now available as a mobile phone app), coupled with the meridian point on the setting circle (which is set to sidereal time), for finding objects not visible to the naked eye, and probably remains the best method for finding Mercury and Venus in daylight.

John 

Edited February 22, 2020 by johnturley