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I know its too open ended to ask this, but in DSS is there anything obvious im missing that would cause the stacked image to contain trails. trying to stack 20 subs of M13, subs look ok, could be a little more focused but nothing i havent stacked before without issue. 

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Are you using a zoom lens? Could the focal length have altered between frames? Though it seems more like mis-registering for some reason. I'm sure I've seen this type of thing before, but no longer a current user of DSS so memory eludes me. Sorry can't be of more help!

Ian

Edited by The Admiral
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7 hours ago, Anthonyexmouth said:

I know its too open ended to ask this, but in DSS is there anything obvious im missing that would cause the stacked image to contain trails. trying to stack 20 subs of M13, subs look ok, could be a little more focused but nothing i havent stacked before without issue. 

What I would do as it looks in this case DSS is doing something strange is reset DSS to default settings and then as Peter said. Sure you haven’t got comet mode selected?

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DSS doesn't like out of focus stars and may ignore them. The result can be registering on camera hot pixels instead, with the result of trailing showing if true stars move slightly between each sub.

You can test for this by reducing the sub resolution by 2 in each x,y direction before stacking - doing this in jpeg (not ideal for imaging) if necessary. Reducing the resolution makes stars tighter and DSS may then stack correctly.

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2 hours ago, Anthonyexmouth said:

ah probably a focus issue then. even with my clothes peg mod my mak 90 is surer hard to fine tune

As I asked before, how many stars does DSS think it's seeing? If bobro is correct and DSS isn't recognizing stars, then you'll either have very few, even with the threshold low, or a huge number, if it's really seeing noise.

Ian

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1 minute ago, Anthonyexmouth said:

With the threshold at 5% it sees 78 then it drops of very sharply a few percent above that

Hmm, I wouldn't have said that was unreasonable. Mostly, you'd set the threshold for a hundred or so. What sort of scores are they getting? You could try stacking without the very poor ones and see if that makes a difference. Can't help feeling there's a setting wrong somehow, but you could try running through some other subs that you know stack OK, and see what you get.

Ian

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11 minutes ago, Anthonyexmouth said:

Haven't kept any as none were really great. They did stack though. How does the scoring work? Seen it but didn't know what it meant

I can't remember the details but I think it's based on FWHM. When you stack (? register) the subs, you can either tick the boxes of those you want to include, or set a threshold for inclusion. It should be in the on-line manual or technical details http://deepskystacker.free.fr/english/index.html

Note this is assuming you do the registering separate to the stacking. If not, DSS will register prior to stacking.

Ian

Edited by The Admiral
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Two things during to mind

1 there is a rogue sub in the mix with bad trails.

2 it has treated the globular as a comet. Though on a prior version 3.3.4 (which I used) you had to manually indicate the comet but I haven't tried the latest version yet.

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Another thing, what alignment mode is being used under the "alignment" tab of the "stacking parameters" screen? It's normal to initially use "automatic", but IIRC with rogue stacks it is sometimes helpful to try another mode.

Ian

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Im not sure you mentioned what camera you were using, in order to reduce the trailing in the raw images you need to drop your sub length a bit (or use guiding). If youre using a CMOS based camera you can increase the gain in order to reduce camera noise and therefore make better use out of the reduced signal that comes of a consequence of using shorter subs.

On top of that, get the focus a bit closer - then DSS should have no problem registering your subs correctly.

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