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ZWO ASI533 Star Detection


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Hi,

I'm using my ASI 533 along with my C9.25 and 0.63 reducer to image galaxies. I tried M81 and M51 both at 150 gain for 180sec exposures. When I bring the images into DSS software, the star detection threshold for M81 could detect only 30 stars with the slider all the way down to 2%? When I stacked the images and brought the final image into Ps, I had to do some brutal levels and curves adjustments to even see the galaxy in the frame. It was worse when I attempted to stack M51 in DSS, where the number of stars detected was just 16! DSS could not stack the 40 or so images that I spent the night capturing. When I switched to my Nikon D7500 and took light frames each for 180sec at ISO800, DSS detected hundreds of stars and stacking was seamless. Has anyone encountered this using a similar setup?

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22 hours ago, recceranger said:

Hi,

I'm using my ASI 533 along with my C9.25 and 0.63 reducer to image galaxies. I tried M81 and M51 both at 150 gain for 180sec exposures. When I bring the images into DSS software, the star detection threshold for M81 could detect only 30 stars with the slider all the way down to 2%? When I stacked the images and brought the final image into Ps, I had to do some brutal levels and curves adjustments to even see the galaxy in the frame. It was worse when I attempted to stack M51 in DSS, where the number of stars detected was just 16! DSS could not stack the 40 or so images that I spent the night capturing. When I switched to my Nikon D7500 and took light frames each for 180sec at ISO800, DSS detected hundreds of stars and stacking was seamless. Has anyone encountered this using a similar setup?

How was your focus? 

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On 09/02/2022 at 21:24, Adam J said:

How was your focus? 

Hi Adam, 

The focus was spot on. I use the EAF AF function via the ASIAIR Plus and it refocus every hour or at a 2 degree variation. I’ve got a clear night at the moment so I’m attempting 300sec exposures on M51 at 150 gain. I’ll see how that goes👍

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9 minutes ago, recceranger said:

Hi Adam, 

The focus was spot on. I use the EAF AF function via the ASIAIR Plus and it refocus every hour or at a 2 degree variation. I’ve got a clear night at the moment so I’m attempting 300sec exposures on M51 at 150 gain. I’ll see how that goes👍

another issue may be the debayering settings, if those are not correct star detection will not work.

Adam

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1 hour ago, Adam J said:

another issue may be the debayering settings, if those are not correct star detection will not work.

Adam

I’m pretty much using the default that came with the camera. I haven’t touched these as I haven’t a clue😅

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15 minutes ago, recceranger said:

I’m pretty much using the default that came with the camera. I haven’t touched these as I haven’t a clue😅

Those settings are in DSS not the camera. 

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7 hours ago, Adam J said:

Those settings are in DSS not the camera. 

Thanks Adam,

Im also using the recommended defaults in DSS. I haven’t touched these. I was able to detect 30 stars on M81 which DSS stacked, but M51 was a no go. I got another 20 lights last night of M51 at 300sec; 150 gain, so I’ll have a go at stacking this evening 

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On 09/02/2022 at 00:41, recceranger said:

When I stacked the images and brought the final image into Ps, I had to do some brutal levels and curves adjustments to even see the galaxy in the frame. It was worse when I attempted to stack M51 in DSS, where the number of stars detected was just 16! DSS could not stack the 40 or so images that I spent the night capturing. When I switched to my Nikon D7500 and took light frames each for 180sec at ISO800, DSS detected hundreds of stars and stacking was seamless. Has anyone encountered this using a similar setup?

The necessity to do a brutal stretch is not a problem, but it is a bit of a problem in this case if you use photoshop for all processing. I would recommend doing some things to the stack in Siril first and then moving the partly processed file to photoshop for the final adjustments (which is often most of the work). You can do a background extraction if necessary, photometric colour calibration and then stretch the image to what you like in Siril. But this has nothing to do with the star issue, just pointed out that with files that need a lot of stretching it can seem "wrong" with the way you need to do it in PS and there are better alternatives.

The star detection issue is hard to advice on without seeing the raw frame itself, but i will guess it has to do with sampling rate/star size and so DSS doesn't count the stars in your images as stars because they are spread over too many pixels. Sampling rate is just a part of this though, seeing and your guiding performance will also effect this.

Try the super pixel debayering setting in DSS and see if it detects more stars:
DSS1.PNG.74f32897560995033dbe48c2b7758db1.PNG

DSS2.PNG.d077b6ba25606e9b2dc9a178634122df.PNG

If that doesn't work, could you attach one raw frame here so we could have a look?

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28 minutes ago, ONIKKINEN said:

The necessity to do a brutal stretch is not a problem, but it is a bit of a problem in this case if you use photoshop for all processing. I would recommend doing some things to the stack in Siril first and then moving the partly processed file to photoshop for the final adjustments (which is often most of the work). You can do a background extraction if necessary, photometric colour calibration and then stretch the image to what you like in Siril. But this has nothing to do with the star issue, just pointed out that with files that need a lot of stretching it can seem "wrong" with the way you need to do it in PS and there are better alternatives.

The star detection issue is hard to advice on without seeing the raw frame itself, but i will guess it has to do with sampling rate/star size and so DSS doesn't count the stars in your images as stars because they are spread over too many pixels. Sampling rate is just a part of this though, seeing and your guiding performance will also effect this.

Try the super pixel debayering setting in DSS and see if it detects more stars:
DSS1.PNG.74f32897560995033dbe48c2b7758db1.PNG

DSS2.PNG.d077b6ba25606e9b2dc9a178634122df.PNG

If that doesn't work, could you attach one raw frame here so we could have a look?

Thanks O, that’s really useful. I’ll have a go and report back 👍

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  • 2 months later...

Hi Folks, Many apologies for the delay in responding. 

I got it sorted. My spacing between the Reducer and censor was off by approximately 6-7mm. Once I solved that and increased exposure time to 300sec per frame as a minimum, the images stack with no issues. Also, I discovered that my collimation was a little off which wasn't helping.

Thanks again for all the assistance and clear skies. 

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