EQ8 EQMOD Drifting Coordinates


This may not be a SGP problem, though someone may, have experienced something similar.

Over time I have found that I have a little RA and DEC drift which has occurred in many sites and polar align
setups. Always the same drift, though, very small and mainly shows up after an hour or two of imaging and I will need to re-centre the target.

On occasion, I will magnify the image to see the shape of the stars, to see how the guiding is going and find the slightest oval shape in the small stars, always the direction.

I have always assumed that it is a small polar alignment problem and have settled on the Sharpcap polar alignment routine as it seems the easiest and accurate.
I recently looked at the RA and DEC coordinates I use for Target settings and in the image header after each
frame and the coordinates keep changing. I do a small Dither every 5 frames and only 2 pixels.

Also EQMOD collects sync points in DXsA and DXsB even though I setup as per the help guide.
I will delete these points and reset park position only to see these points again when I park and the mount parking a little to the East of where I reset park too.

I don’t understand why the original RA-DEC coordinates I set change, if only ever so slightly over time?
Is there a sync behaviour in EQMOD I’ve missed. Maybe there’s a problem with the mount encoders?
I use PHD2 for guiding and it appears to guide ok, though the drift remains.

Any clues welcome.


You will want to disable the encoders on the EQ8. They are low-resolution. More importantly, they are prone to corrosion which then throws off tracking.


ok, must they be turned off in the handbox, or in eqmod?


@Werner, I believe they can be turned off via either. In EQMOD, it will require widening the window to uncover the “secret” options (only available in newer verions of EQMOD):

There are many who will recommend not using the hand paddle at all (ie. EQ DIRECT) if using EQMOD.


OK i need to update :wink: i don’t use the handbox i have eqdir… thx

Thanks for the tips.
I noticed in the EQMOD screen shot, that, the sync points in DxA-B are active?
This is the same for me. I have deleted these and it doesn’t seem to do much.

Also, I live in the southern hemisphere and I read somewhere that EQMOD 2 as fixed a problem of RA drift
down here. I tried to find the pdf of that recent fix, but I couldn’t find it again? Maybe you have seen this?
I have been using an earlier version EQMOD.

Hi Scott,
The DxSA/B are not points being collected/added to a pointing model but is an on-the-fly adjustment to reconcile the point model against actual sky position. It is changes in DxSA/B which allows the mount to converge on the target during a “Centeri Now” operation in SGP. That’s my understanding of it at least.

Not sure about the Southern Hemisphere RA drift problem - don’t recall seeing anything on that before. But I am a “Northerner” :=)

There are others on the forum who can make better suggestions than me, but when I see drift like you describe, I usually put it down to either weight imbalance or polar alignment issues. There are some good tools out there for dialing in polar alignment, such as Polemaster/Sharpcap but those can still be fine tuned by using drift method (such as PHD2 Drift Align tool).

Perhaps also worth looking at your Dec backlash.