Help with NEQ6 please

[dwc]

I'm trying to understand what I think is an issue with the normal movement of my NEQ6.

This image is a series of 10x 40second unguided captures of a star, overlaid, and cropped to remove the others.

Ignoring the focussing (!), what does this tell me about the movement of the mount?

The thing that concerns me most is that it is Z shaped, but should I also be concerned that it is drifting so much in the first place?

I've noticed similar behaviour taking long lunar captures - partway through the avi there is a clear "swerve" of the image.

I just went out to check my PA, unfortunately where Polaris "should" be is obscured by a tree branch, but the fact I can't see it might be ok - at least I can't see it in a "wrong" position.

When I last did a full PA I could see it in the correct place.

[Thalestris24]

Hi

I can't say for sure but it's likely to be a combination of poor PA, intrinsic tracking errors, balance, lack of guiding etc. - all magnified by a long focal length scope!

Louise

[dwc]

Thanks Louise, not too many things to worry about then ....

So I can work on the PA and balance - I haven't rebalanced for a while and certainly not with the DSLR attached.

Guiding is something I need to learn, but I guess there isn't much point starting until I know the mount is working properly.

What I'm really worried about though is whether there is also a mechanical problem, and I'm assuming "tracking errors" suggests there could be.

I forgot to say, it is pier mounted, not tripod.

[brantuk]

You might have a bit of clutch slip in one axis or the other. It does look like the scope has moved during tracking. Another possibility is cog mesh issues or a worn/broken cog or worm gear. I'd be tempted to get the mount serviced if you can't work out or fix the problem. Try Graham at AstroTec - he does a great job for around £90.

[Thalestris24]

Hi again

*I think it's unlikely to be a mechanical problem i.e. fault with the mount, as such. Being mechanical devices, all mounts have periodic and other random errors. I imagine it's quite challenging to get such a long focal length to behave, even with guiding. Other problems can be caused by flex, cables dragging etc. I'm not sure how you took the exposures - if you touched the mount or camera, that would have had an unwanted effect. You have to appreciate the tiny amounts of movement involved and how a very small disturbance can mess up a sub. Setting your rig up properly is the first step towards achieving good guiding and imaging. If you can't see Polaris then you need to drift align. That requires being able to see roughly East or West and roughly South close to the meridian. Balancing a mount for imaging is slightly different from balancing for observing. You need to unbalance slightly in order to compensate for backlash. Once you're balanced and everything is rigid and cables attached to prevent drag, you can do the PA. Then you should be ready to guide. I think trying to capture images without guiding would likely be difficult. Maybe you have a reducer? That would help. I only have experience of imaging at 750mm on an heq5 but the principles are the same. I'm sure there are other c9.25 owners on here that can give more specific advice.

Louise

Edit: I'm assuming it's a new mount?

[Tinker1947]

You don't need to see Polaris to do Polar alignment with the NEQ6 it will run through a list of bright stars to choose from, pick one that's easy for you to view, do this a couple of time on different stars, the manual will show you how, get the balance sorted out this with your FL needs to be right, that should sort it out.......

[dwc]

Thanks both, lots to think about.

I've had the mount just over a year, but only on a pier for 6 months. I've only really started trying to image with it recently. It was purchased 2nd hand, but from a major dealer as a part exchange.

I used APT to control the DSLR, and didn't touch the mount, scope or camera for the duration. I think the pier is solidly concreted in, when I'm watching LiveView I don't see any movement just walking around the shed.

I'll certainly start by rebalancing and aligning, I've never tried a drift align so that should be fun. I do get to see Polaris sometimes, it all depends where it is in relation to the branches! And of course I can only do that in winter when the leaves are gone

The cables are reasonably loose, but I'll work on making sure they can't drag.

[sbooder]

When the mount is off and unloaded and both clutches on tight, do you get excessive movement in either axis if you try and wobble them?

[r3i]

Hi

I can't say for sure but it's likely to be a combination of poor PA, intrinsic tracking errors, balance, lack of guiding etc. - all magnified by a long focal length scope!

Louise

Think you're right Louise.

Looks to me like a combination of:

 1. PA error - causing the drift from bottom left to top right (or the other way round)

 2. Periodic error - causing the sine wave.  IRIC the period of the worm on an EQ6 is about 8 minutes, so if you've capture around 400s worth of imaging, you've just about got a full cycle of the worm, which is probably why you're seeing a "Z" shape.

Both effects become very apparent by the fact the images were taken unguided with a very long focal length (I'm presuming you took them with your C9.25?)

Remedies:

1. Check PA

2. Adjust the worm mesh to get rid of any excessive play (see Astro Baby's excellent site for details: http://www.astro-baby.com/EQ6%20rebuild%20guide/EQ6%20worm%20alignment.htm)

3. Use autoguiding, ideally off axis guiding for such a long FL scope.

[Carina Lass]

You've been infected by the Zorro Bug.

[m.tweedy]

You've been infected by the Zorro Bug.

cured by a strong dose of guiding