SharpCap Forums

What does this drift graph tell me? Mount is a skyguider pro, no guiding. Does it tell me my PA is off? (Did with SC) does it tell me something else? Or is this expected behavior of the SG pro?

Well there's definitely a lot of drift

The SGP does have a lot of periodic error, so if its unguided, there will be drift in RA. To go deeper, as per my understanding (which may be wrong), more information is needed.

1. What's the total time represented in the graph? Unguided, even a small dec drift will accumulate over time.

2. The orientation of RA and DEC with x and y. That can be done within SC 4 easily by platesolve (only) and then seeing the onscreen markers.

If there is drift in DEC as well even after good PA, something may be loose in the SGP.

I have had reasonable drift in the past. Now this drift is just only taken over 10 minutes, so that might be a bit short and as such might not be very representative. I can't do the platesolve in Sharpcap, as I do not have this installed (does that make any sense when not having a GoTo). In any case, the target was the Flaming Star Nebula, from the Netherlands between 0100 and 0300, if that will be any help. After I stopped imaging, I noted the SGP was not bolted perfectly tight on the tripod, it could wiggle a bit when I gave it a little bit of effort, so not something too serious I think. When live stacking I can visually see after a minute or 20 or so that there is movement, as the stars are aligned, but the pictures of course arent.... in the direction of the dec axis.

Hopefully the tightening of the mount will solve the problem.

You can also just upload a sub to astrometry.net for solving.

There you go...

Can you give the screenshot after clicking the "grid" button on top of the image? That will show the angles

Here you go

Total time in the drift graph is 18m

So looks like you have drift in both NS and EW. EW could be expected, but NS seems large. That plus the rotation indicates PA error.

Unguided will have a drift, the calculator at http://celestialwonders.com/tools/driftRateCalc.html shows that at a PA error of 2 arc-min, you can expect a cumulative drift of 8 as (in your case, about 16 pixels) after 18 min. Yours is in the region of 100 pixels

Putting in your numbers ( approx 100 pixels = 200 as, Dec 34 degrees, and time of 18 min) into the reverse calculator at http://celestialwonders.com/tools/polarErrorCalc.html indicates in the region of 50 minutes.

If the initial alignment was done accurately with SC, it may have shifted - could be a loose mounting, the scope/camera flexing slightly, or even if you are set up on grass, tripod legs sinking in just a little bit!

Open to any corrections from Robin or anyone else.

Could you explain to me 'drift in NS and EW'... I am not yet really up to snuff with things like drift, RA, dec and how this translates to what you see.. .