Is my NEQ6 guiding too good to be true?

[nikanj (Andy)]

When I compare the total RMS error figures I get in PHD2 to other NEQ6 users mine are significantly better. My NEQ6 is unmodified and I see a typical total RMS error of around 0.5-0.6 arc seconds with values as low as 0.3 arc seconds when seeing is good. Stars are always nice and round except for very slight strangeness in the corners which I'm 90% sure is from either back focus distance or tilt and not tracking. The results are so good it makes me suspicious I've messed up the settings in PHD2.


PHD2 automatically loaded the pixel size/scale for my ASI120MM guide camera so I assume that's correct. I inputted my focal length as 600mm as I'm using an OAG on a 800mm Netwonian with a 0.75x reducer (Starizon Nexus).


The only complaint I have is that I have significant DEC backlash so DEC can spike as high as 1.5 total RMS error before recovering. I'd like to belt mod and hypertune my NEQ6 but at the same time I'm afraid of messing up a good thing.

What do you all think? Are these results legitimate or did I mess up the settings somewhere? Should I hypertune my NEQ6 or just leave it as is and perhaps fiddle with the DEC pressure?


Here are some screenshots of my guiding graph and PHD2 Guiding Assistant output for reference.


https://i.imgur.com/2hEm2fJ.png


https://i.imgur.com/kN5QNgM.png

[Nikolas (Nik)]

I have mine belt modded and it works like yours without the Dec backlash. it is a great mount.

[nikanj (Andy)]

Thank for the input Nik.


I'll give the belt mod a shot and hopefully tune out the DEC backlash too while I'm at it.

[Todo43 (Lachlan)]

Hi Andy,


I have too been wondering this. I was imaging Rho a couple nights ago and was getting 0.25" guiding on my unmodified NEQ6. 600mm scope and OAG with 120MM. I thought that there was no way that this could happen but I think it was just a combination of spot on polar alignment and seeing that night.



I am intrigued about the spikes that you talk about. Do they come around often? If so, it could be an issue with the wormgear? If it is quite random however, it is quite possible that wind or something picked up and created a disturbance. Cars and trucks going by can even effect it depending on your distance from a road.



Lachlan

[nikanj (Andy)]

I'm very precisely polar aligned too. I'm also well below the mount's payload capacity and pay very close attention to getting the balance as good as possible. I think these things probably contribute more to my better than typical guiding than having some sort of golden sample.



To be honest I'm not sure what is causing the DEC to spike up on occasion. I don't think it's wind or vibration as I assume that would also affect RA. It could be clouds but again that should affect RA too.



I'm thinking it is an issue with the worm gear/roller engagement pressure. Either binding or backlash. But it's not periodic.

I've decided to belt mod my mount anyway. The kit is arriving tomorrow so I'll report back on how it goes and whether it sorts out my backlash issues.

[nikanj (Andy)]

I ended up going through with the belt mod (thanks to Sidereal Trading for getting it out so quickly) and also took the opportunity to replace the worm gear bearings with SKF and re-lubricate everything with Super Lube.


I was a smooth process. I can feel a lot less backlash in DEC now (I can't physically wobble it like I could before). It's also much quieter and smoother.

Haven't had a chance to try it out in the real world yet as we've got nothing by clouds for the next couple of weeks in Melbourne .


https://i.imgur.com/6S3KZBD.jpg
https://i.imgur.com/kwc2PML.jpg