Blobby stars after stacking

[pook]

Hi,

I have a problem with DSS. After stacking, the stars are weird blobby rings with a pin point centre. None of the subs have this, and focus was correct.

Here's a shot of the focus using a mask.

Here's one of the subs.

and here's what comes out of DSS.

Why is this happening?

[Deneb]

looking at your star shapes, they look like a collimation issue, i've only replicated results like this when my collimation is slightly offset.

If look at the stars, they have a triangle shape appearance.

Nadeem.

[pook]

So why is the stacked version the way it is?

I've double checked collimation. secondary appears to be perfectly aligned with the draw tube, and the primary appears perfectly aligned both with the cheshire and a barlowed laser... and also a collimated laser. Everything seems to agree on collimation.

I'm really pulling my hair out here. With this stupid mirror clip issue, and now this.

Grrrr.

[edit]

This is a tight crop from the full frame.

[Psychobilly]

Have you checked all the subs and excluded any dodgy ones for the file list....?

Whats happening to FWHM values between the early and later frames...?

Have you got dark and hot pixel removal selected inthe cosmetic tab...? It can sometimes cause hollow stars...

Peter...

[pook]

Have you got dark and hot pixel removal selected inthe cosmetic tab...? It can sometimes cause hollow stars...

Peter...

Aha! That sorted it! Thanks