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Posted (edited)

Hello,

Here's my first shot at M35.  Primaluce 72ED, Astronomik CLS-CCD filter, ASI 178MC, Pixinsight.  Only 20 lights of 30 sec.  Biases & flats applied.  There's definitely some weird things in there (a line of small red dots towards the bottom right hand corner, about an inch or so in from each edge).  I don't think its a processing artefact, because it appears in the first integrated image.  I tried to upload 16 bit darks but PI is again not letting me do that for some reason (but it does let me load 8 bit darks).  I'm thinking it could be hot pixels (?) but wouldn't they be removed by the biases?  I tried processing the lights with both 8 bit darks added, and no darks, and the image was better without the 8 bit darks.  In both cases that little pattern is there.  Does anybody have ideas where that's coming from (or has anyone experienced that before)?

Cheers,

Vin

(PS: that weird motif is best seen by zooming in on the image.  And then you can see it appears in other parts of the image too.  It seems to already be in the image after integration, but before any other processing is done.  Is there such a thing as a stacking artefact - if so, how could I avoid that?  Thank you!)

 

M35 PI bf.jpg

Edited by vineyard
added PS

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I can't help with the cause of the artefacts/dots in the image but have you tried using something other than PI - like Deep Sky Stacker?

I usually stack in APP these days but if there is something odd in the resulting integration I often throw it all into DSS to see if I get the same effect. It's free, dead easy to use and worth a go - unless you're Mac only and don't have access to a PC.

Adrian

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2 hours ago, vineyard said:

There's definitely some weird things in there (a line of small red dots towards the bottom right hand corner, about an inch or so in from each edge).  I don't think its a processing artefact, because it appears in the first integrated image.

Vin,

First it is a very nice M35 image, well done. The artefacts that you are seeing are walking hot pixels that have not been eliminated by your darks/bias, which sometimes happens. By walking pixels I mean that these are the same pixels on the sensor for each group, which give the appearance of walking across the image as each of your frames drift slightly between captures, probably due to slight error in polar alignment. If you look closely you can see repeat patterns for red, blue and green pixels throughout the image. Other than cloning them out which can be done but is very tedious, the best way I know to avoid them is to dither during capture then use sigma stacking. Given that you have some natural dither due to drift in your individual images, you could try sigma stacking on the set to see if that removes them. The purpose of sigma stacking is to reject outliers, so if you set sigma at something like 2.5, these hot pixels will be outliers in the stack and very well may be rejected as stacking is on the stars, not the individual sensor pixels. I hope that makes sense, so perhaps give it a try anyway.

Good luck.

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Thanks Geof.  Had never heard that phrase about walking hot pixels!  Yes you're right about the PA - where I took those from I couldn't see Polaris and sky was also restricted for drift alignment so I used the Mount Model tool on EKOS.  Have to read up about dithering.  Will try the sigma stacking on these lights and see what happens.  And thanks too Adrian, that's a good idea - it'll be interesting to see how the two different softwares compare (I'm Mac based but have an emulator b/c AS!3 is so brilliant).  Will report back - cheers, Vin

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Posted (edited)

ss6.jpg.37d655fd769147dc680cad8708bfab43.jpg

Hi

Nice shot.

There's also a smaller, more distant cluster which I think fits the fov if you were going to return to have a go at those hot pixels.

Cheers 

Edited by alacant
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Thanks Alacant - is that NGC2158?  I did have a go at that the same night - posted it here & its the same darn wandering hot pixels problem in there...something to address on both those targets next time!  Cheers, Vin


 

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Posted (edited)
3 hours ago, vineyard said:

is that NGC2158?

Yes, I think so; they should both fit in the same field.

I'm with @geoflewis on this. I think dithering and the sigma thingy stacking would lose all the hot pixels. The more frames, the better is the rejection. At least that's what we find on a cheepo dslr.

Cheers

Edited by alacant
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