ZWO ASI533MC - Are these sub noise levels reasonable for this camera?

[abmwinnoch]

Hi. On the suggestion of the good folk at FLO, I'm posting this query on here. I've just bought the ASI533MC so I can image on both my rigs at once, joining my existing ASI294MC camera.

First impressions are good; very impressed with how quickly the camera cools and maintains temp amongst other things, but one thing I have noticed is that the noise levels seem higher than my 294.  See a typical sub below. It means that I'm having to apply more noise reduction after stacking than I'm used to doing at same settings with my 294.

Does anyone who has this camera have a sub with IC 1848 - SoulLIGHT180.001202022-12-200025.fitssimilar setting to me, that they can post for comparison? I had the camera at 120 gain (though I believe 100 is a better level for this camera), cooled to -20 and this is a 180 second exposure. Just seems a bit noisy to me- wanting to check I don't have a dud or there is a setting somewhere that needs set. Thanks!

[vlaiv]

Looks perfectly fine.

39 minutes ago, abmwinnoch said:

It means that I'm having to apply more noise reduction after stacking than I'm used to doing at same settings with my 294.

You have to note that ASI294 has 4.63um pixel size and ASI533 has 3.76um pixel size.

That is x1.5 in signal level per pixel if they are both used on same scope. Difference can be even bigger if there is additional difference between scopes.

If you use both cameras on same scope - you need x1.5 more total imaging time with ASI533 to match 294 (if they have the same QE, and they probably do).

What scopes are you using with these cameras?

[abmwinnoch]

1 hour ago, vlaiv said:

Looks perfectly fine.

You have to note that ASI294 has 4.63um pixel size and ASI533 has 3.76um pixel size.

That is x1.5 in signal level per pixel if they are both used on same scope. Difference can be even bigger if there is additional difference between scopes.

If you use both cameras on same scope - you need x1.5 more total imaging time with ASI533 to match 294 (if they have the same QE, and they probably do).

What scopes are you using with these cameras?

Okay that makes sense and would explain the noisier data. I should probably have considered that before buying this model- The rarity of clear, windless nights means less time per target would've been a better outcome, at least until I buy a hyperstar one day! I haven't decided which way round is best yet- 294 on the Celestron C925 (usually with with reducer) and 533 on the WO ZS61iiAPO or the other way around. In terms of framing, the 294 gives a wider field of view so would probably be better employed on the William Optics scope with the tighter, square framing of the 533 being good for framing targets like planetary nebula and galaxies.
In this case, the FITS image above was from the 533 on the WO.

[vlaiv]

12 minutes ago, abmwinnoch said:

Okay that makes sense and would explain the noisier data. I should probably have considered that before buying this model- The rarity of clear, windless nights means less time per target would've been a better outcome, at least until I buy a hyperstar one day! I haven't decided which way round is best yet- 294 on the Celestron C925 (usually with with reducer) and 533 on the WO ZS61iiAPO or the other way around. In terms of framing, the 294 gives a wider field of view so would probably be better employed on the William Optics scope with the tighter, square framing of the 533 being good for framing targets like planetary nebula and galaxies.
In this case, the FITS image above was from the 533 on the WO.

Do keep in mind that you need some "pre/post processing" for best results with C925 (even with focal reducer) and such small pixels.

I'd keep resulting sampling rate at around 1.5"/px in either case.

ASI294 with x0.7 reducer on C925 will give you ~0.58"/px. I would bin such data x3 after stacking and before processing

ASI533 is going to be even higher sampling at ~0.47"/px - again at least x3 bin.

If you use them natively - then bin x4.

[abmwinnoch]

16 hours ago, vlaiv said:

Do keep in mind that you need some "pre/post processing" for best results with C925 (even with focal reducer) and such small pixels.

I'd keep resulting sampling rate at around 1.5"/px in either case.

ASI294 with x0.7 reducer on C925 will give you ~0.58"/px. I would bin such data x3 after stacking and before processing

ASI533 is going to be even higher sampling at ~0.47"/px - again at least x3 bin.

If you use them natively - then bin x4.

Sorry, what do you mean by- "if you use them natively?"

[scotty38]

4 minutes ago, abmwinnoch said:

Sorry, what do you mean by- "if you use them natively?"

Pretty sure he means without the reducer on th3 C9.25 so you'll need to bin that bit more.

[abmwinnoch]

So, I'm currently imaging with 3x3 binninCaldwell 9-CaveLIGHT240.001002022-12-220070.fitsg and the subs look much, much noisier than 1x1; that shouldn't be should it? FITS file attached- note, it's not fully dark yet so the image is a bit of a mess but you get the idea.

[scotty38]

I see what you mean, does look a bit odd. How are you binning at acquisition time?

[Dave Matison]

I have found that liberal dithering greatly improves the apparent noise of my 533mc pro.   I love the camera, almost as much as the 2600mc pro.

[abmwinnoch]

Caldwell 9-CaveLIGHT240.001002022-12-220076.fitsBetter example now it's dark. Actually I'll reserve judgment till I've stacked a few of these. Certainly the signal (target) seems nice and strong.

[abmwinnoch]

11 minutes ago, Dave Matison said:

I have found that liberal dithering greatly improves the apparent noise of my 533mc pro.   I love the camera, almost as much as the 2600mc pro.

I've been dithering every 4 frames; more?

[abmwinnoch]

19 minutes ago, scotty38 said:

I see what you mean, does look a bit odd. How are you binning at acquisition time?

Just trying, for the first time to use 3x3 binning as suggested above. Started doing darks with this binning level, in preparation.

[scotty38]

1 minute ago, abmwinnoch said:

Just trying, for the first time to use 3x3 binning as suggested above. Started doing darks with this binning level, in preparation.

so you're binning after stacking and not at acquisition time?

[abmwinnoch]

16 minutes ago, scotty38 said:

so you're binning after stacking and not at acquisition time?

No- binning at acquisition time. I can't seem to get binning to work in DSS and no idea how to do it after that, so simplest for me to Bin at source.

[scotty38]

Ok that's what I was asking, how are you doing it at acquisition?

[tomato]

If it’s a OSC camera won’t you lose the colour data if you bin when taking the subs?

[abmwinnoch]

1 hour ago, tomato said:

If it’s a OSC camera won’t you lose the colour data if you bin when taking the subs?

Just about to find out as I stack the meagre few frames I got before the rain. Don't think so though- sure I've tried stacking binned frames before ages ago. Will report back

[abmwinnoch]

1 hour ago, tomato said:

If it’s a OSC camera won’t you lose the colour data if you bin when taking the subs?

Nope full colour, but noisier than the front row of a death metal concert.🤨

[ONIKKINEN]

ASTAP (free) has a binning tool which works with colour images that you can use after capture. Easiest way is to stack unbinned and bin the stack before making any adjustments. You can also batch bin your subs and then stack them, same result either way (almost).

 

[abmwinnoch]

OK, think I'll 'bin' this experiment and return to using the full resolution of the camera. I've never been able to wrap my head around the concept of throwing away a third or a quarter of the camera resolution I've paid for and I also don't understand how the focal length of telescope matters? Surely a camera is telescope agnostic in that all it's 'seeing' is an analogue image from the focuser; how can it 'know' whether this image is coming from my 360mm WO or from a reduced 2888mm focal length of the C925? It's all just billions of photons landing on the sensor. Sorry despite having it explained to me on various fora over the past year or more, still don't get it. Thanks for trying though!

[abmwinnoch]

15 minutes ago, ONIKKINEN said:

ASTAP (free) has a binning tool which works with colour images that you can use after capture. Easiest way is to stack unbinned and bin the stack before making any adjustments. You can also batch bin your subs and then stack them, same result either way (almost).

 

Thanks, I've got ASTAP; i'll give that one final go, before abandoning the experiment and returning to 1x1 imaging and living with the noise.

[ONIKKINEN]

6 minutes ago, abmwinnoch said:

Thanks, I've got ASTAP; i'll give that one final go, before abandoning the experiment and returning to 1x1 imaging and living with the noise.

How do you quantify the amount of noise in bin1 vs bin3? If its with a stretched file you should make sure that they have an equal stretch. You should also view both at 100%. Bin3 will have 3x signal to noise ratio or in other words be equal to a bin1 exposure of 9 times the length.

It just doesnt make sense (cannot be true) that the bin3 image is noisier.

[abmwinnoch]

1 minute ago, ONIKKINEN said:

How do you quantify the amount of noise in bin1 vs bin3? If its with a stretched file you should make sure that they have an equal stretch. You should also view both at 100%. Bin3 will have 3x signal to noise ratio or in other words be equal to a bin1 exposure of 9 times the length.

It just doesnt make sense (cannot be true) that the bin3 image is noisier.

Hmm; this was just visually looking at the subs- I admit I've not been able to capture enough 3x3 subs yet to directly compare a stacked result- below is a screenshot snip of the subs with 1x1 on the left and 3x3 on the right at the same scale. The 3x3 looks far noisier to me.

 

[abmwinnoch]

1 hour ago, ONIKKINEN said:

ASTAP (free) has a binning tool which works with colour images that you can use after capture. Easiest way is to stack unbinned and bin the stack before making any adjustments. You can also batch bin your subs and then stack them, same result either way (almost).

 

Just used it and it seems to work well- much reduced noise. Much smaller file too- from 51mb down to 1.84mg- does that seem right or do I need to alter some settings in ASTAP?

[ONIKKINEN]

Just now, abmwinnoch said:

Just used it and it seems to work well- much reduced noise. Much smaller file too- from 51mb down to 1.84mg- does that seem right or do I need to alter some settings in ASTAP?

Fewer pixels so the filesize is smaller naturally.

By the way ASI fitsview is not very useful for actual image analysis as it stretches the image with some arbitrary set value so you are not really seeing the raw data. Its better to view the image in something like Siril where you can make objective measurements on the pixel values/standard deviation/whatnot and try to make an educated guess on the sub. But ultimately i dont recommend viewing subs at all, just check their statistics when stacking (and maybe reject the worst ones) and only judge the final stack on quality.