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Graham,
DSS needs at least 8 stars to successfully proceed and the critieria is that they need to be reasonably round (DSS manual)
How many frames are you trying to stack?
Are they RAW or JPG?
Try doing a "compute offsets" first to see the score DSS applies to each frame. This does not start any aligning etc, only used to analyse your data and any possible reasons for DSS not wanting to stack.
DSS also doesn't like too much field rotation. See my example below in the animated GIF. The gif is only 2 frames but the 1st is a score of 4712 (highest and therefore DSS uses this as the base and therefore a dX and dY = 0) The 2nd frame is almost the worst as indicated by a relatively lower score of 4238 but this frame has the highest field rotation showing it has deviated by +3 pixels in the X direction and -3.5 in the Y - ie my mount is not perfectly polar aligned and/or there is flex. These shots were unguided too btw.
Image 1 = Offsets. Note that I have ordered top to bottom by filename and hence the top is earlier in the night, bottom later in the night. Note too the dX is consistently increasing from - to + which is clear indicator the sky is rotating slowly wrt the mount due to inaccurate polar alignment.
Image 2 = animated gif. Pay attention to preview screen and note how the stars seem to jump slightly. On a mount perfectly polar aligned, there would be no jump in the gif animation.
This might help you diagnose why DSS is not stacking. There is almost always a logical reason why it won't. This is where I struggled in earlier days to get it to stack more than 2 or 3 out of 20 odd frames. In this example, I was able to stack all frames as DSS was happy with these tolerances.
I hope this helps you. Good luck and if in doubt, keep bugging us as I am sure many others may have a similar problem and we'd be happy to share our knowledge gained.
Cheers,
Darrin...
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