Jump to content

Narrowband

eq6: can I fix the RA circle relative to polarscope?


Recommended Posts

Hi everyone

I set Polaris at the bottom of the polarscope and the RA circle to zero. I tighten the setting circle screws. I set the HA given by Synscan. Great.

I now set home position. The RA circle rotates with the RA axis. As soon as Iock the clutch and align, the RA circle no longer moves with the RA axis and so I lose my Polaris position relative to the polarscope.

I'd like to be able to set Polaris relative to RA once and leave it set.

Questions:

1. with the clutch locked and motor driven, should the RA circle rotate with the RA axis? Mine doesn't.

2. Must I set RA-polarscope every time I setup?

Cheers

 

Link to comment
Share on other sites

  • Replies 25
  • Created
  • Last Reply

The setting circles, in my experience on the EQ5 and EQ6 mounts are worse than useless. They don't lock in place reliably and rotate when the mount rotates around the axis, which is not what you want.

So:

1. No. You want the mount to rotate around RA but the circle to remain static, so any change in position in RA is reflected by a new value as measured off the setting circle.

2. With your setting circles, yes. Though you could just make your own marks on the mount, an arrow on the moving part of the mount and marks to indicate 5 degree intervals around the 360 degrees of the axis (or the other way around). Then ignore the setting circles and use your own marks to indicate the hour angle. Make sure you set your hand drawn arrow to zero when the small Polaris circle in the polar scope is at the 6 o'clock position (below); there are ways to make sure the Polaris circles is as close to 6 o'clock as possible but I don't think that is necessary. I think for this set up the accuracy will be low (but maybe higher than just guessing where the Polaris circle should go), but polar scope polar aligning always is a bit rough and ready anyway, but this would give you a reasonable stab at polar aligning. Just also think that your marks need to be visible at night with a red torch, so probably don't make them with a red marker, and be aware that if you want to sell the mount on this may be a reason someone tries to knock money off the asking price.

James

 

Polaris transit.png

Link to comment
Share on other sites

Hi James

Thanks for the clear answers.

TOL: The polarscope will always be at a fixed angle when the RA is at home position.

1. I set home position. 

2. I set 0 hours on the RA circle.

3. I rotate in RA to get Polaris at 06:00

4. I note the time angle on the RA and set that time angle when the mount is at home position.

5. Rotating to zero will always put polaris at 06:00 hours 

 I reckon that unless I unscrew the polarscope, that time angle will always be the same.

Any good?

Cheers

 

Link to comment
Share on other sites

A. Yes, the position of the polar scope reticle is fixed to the RA axis, unless you take the reticle out and rotate it so it is in the transit (6 o'clock) position when the mount is in the home position, but this is hassle, stressful, dangerous, potentially costly, and totally unnecessary :)

B. If you are going to use the Hour Angle method to position the small Polaris circle in the correct position to polar align, then you need to set the RA circle to zero when the Polaris circle is at the 6 o'clock position, NOT in the home position (unless you have disregarded my advice in "A" and made the two the same).

C. If you set the RA circle to zero in the home position, you in effect have no idea where the Polaris circle is. You can look up the polar scope and it might be at 3 o'clock (but you've no real idea if it is at 2:30 or 3:30, or if the tripod is severely not level it could be at 4 o'clock. You need the zero your setting circle when you are sure the Polaris circle is at a specific position and 6 o'clock or 12 o'clock is best as you can then adjust the altitude of the mount and confirm the Polaris circle ascends or descends in a straight line, using a very distant straight target. These things are so hard to explain in words!!!!!


James

 

Link to comment
Share on other sites

 

8 hours ago, jambouk said:

C. If you set the RA circle to zero in the home position, you in effect have no idea where the Polaris circle is.

But I do know where it is. I think!

We agree the that the RA axis and the polarscope are fixed.

From the home position, Polaris in transit -with my mount only- is at 21:10. So:

1. Zero the RA setting circle in the home position. Polaris is not in its transit position.

2. Rotate to 21:10 and lock RA. Polaris is now in its transit position.

3. Rotate the RA circle to zero.

4. Release RA and set the HA.

No matter what I do with the motors, Polaris always comes back to the same place at 2 above.

Am I close?

 

 

 

Link to comment
Share on other sites

I think what you're trying to do is explained in the following two videos from astronomy shed - currently about to do it myself on my AZEQ-6GT, you'll have to run through to the relevant bits but he explains it fairly well

 

 

 

 

 

 

 

Link to comment
Share on other sites

18 minutes ago, jambouk said:

Where does 21:10 come from?

Sarting from the home position with the RA circle set to zero, rotating the RA axis to 21:10 puts polaris in its transit position at the bottom of the polarscope.

Link to comment
Share on other sites

20 minutes ago, jambouk said:

We must remember the setting circles ilin the EQ6 don't work. Unless you've worked out how to get them to work.

I suppose they do, but not without having to jump through hoops! 

Using the steps above, nothing I've tried so far prevents Polaris coming to rest where it should. Please by all means prove I'm wrong and this has been a coincidence.

In the end, there are so many versions of how to polar align an eq6 on the 'net that I think the only way to do it is to work it out onesself.

Thanks for the video links. What he omits to say, is that his proceedure must be performed every time the mount is moved.

Thanks again.

Link to comment
Share on other sites

4 minutes ago, alacant said:

 

Thanks for the video links. What he omits to say, is that his proceedure must be performed every time the mount is moved.

Thanks again.

No.. you set the hour circle up once - lock it and then use it forever after to set the polar scope position from the hour angle given by the handset. You still need to polar align but it provides a way to accurately position the little circle in the polar scope. 

 

 

Link to comment
Share on other sites

6 minutes ago, russp said:

you set the hour circle up once - lock it and then use it forever

But it cannot be locked relative to the polarscope: on an eq6, the RA setting circle does not rotate with the RA axis when the axis is locked and motor driven. That's the problem; it ends up in a random orientation dependent upon where the motors have taken you.

Link to comment
Share on other sites

You would need to mark the two white halves of the mount around the RA axis. One half moves the other stays static. Put an arrow or line on one half as your static marker, and then you'd need to carefully mark the other half in hours and minutes, or just in 5 degree intervals around a 360 degree ring...

Else do a very a rough and ready polar alignment with the polar scope (basically so rough that you just put Polaris in the cross hairs) and the if you have the Synscan handset do a polar alignment handset routine which is far more accurate and probably easier.

James

 

Link to comment
Share on other sites

5 minutes ago, alacant said:

Does your RA circle rotate with the RA axis when being driven or only when not?

It's a mechanical fixing - makes no difference whether it's driven or not the RA circle rotates when the mount moves around the RA axis on mine.

 

Link to comment
Share on other sites

I have a CG5  rather than a EQ6 and have the same problem. I hope I've understood your problem correctly, but my solution was to tape the setting circle to the RA axis of the mount in the required position. Only needs doing once if you are only using the setting circle for  polar alignment. Belt and braces but good enough for polar alignment at the start of each  session. 

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.