ZWO Cameras is there a real difference between the ASI290MC and the ASI462MC

[wornish]

I have the 290MC and find the images I take of Jupiter to be very noisy.  Even if I stack thousands.

Or is it just the usual UK seeing issue?

 

This is the best 5% of 15000 Frames

Edited August 25, 2021 by wornish
added image

[vlaiv]

That is extremely large Jupiter image.

What scope are you using and are you using barlow to get to that scale or do you drizzle?

In either case - you are loosing SNR to gain "empty" resolution. Level of detail is suitable for the image of this size:

Which is 20% in both height and width - or 1/25th of original image by surface.

Back to original question:

ASI290 has better QE in visible part of the spectrum, has maybe a tad higher read noise. ASI462 is much better for IR imaging - at around 850nm as it is much more sensitive (it is more sensitive in IR part than in visual).

Pixel size is the same and so is size of sensor itself.

1 hour ago, wornish said:

Or is it just the usual UK seeing issue?

What are your capture settings?

[wornish]

I am using my Celestron Edge HD 9.25.  Focal length 2350m.  No Barlow.  No drizzle.

I used Sharpcap to do the capture in  3 sessions each of 5000 frames joined in PIPP using the Join function.

Stacked in Autostakkert 3, Wavelet sharpened in Registax 6.  Final tweak crop and and enlargement 2X in PS

 

Settings were.

[ZWO ASI290MC]
FrameType=Light
Pan=568
Tilt=248
Output Format=SER file (*.ser)
Binning=1
Capture Area=800x600
Colour Space=RGB24
Temperature=26.3
High Speed Mode=On
Turbo USB=100(Auto)
Flip=None
Frame Rate Limit=Maximum
Gain=300(Auto)
Exposure=0.2470ms
Timestamp Frames=Off
White Bal (B)=99(Auto)
White Bal (R)=56(Auto)
Brightness=1
Auto Exp Max Gain=300
Auto Exp Max Exp M S=30000
Auto Exp Target Brightness=100
Mono Bin=Off
Background Subtraction=Off
Planet/Disk Stabilization=Off
Banding Threshold=35
Banding Suppression=0
Apply Flat=None
Subtract Dark=None
Display Black Point=0
Display MidTone Point=0.0789066279632318
Display White Point=1
Notes=
TimeStamp=2021-08-24T22:23:49.0600750Z
SharpCapVersion=4.0.8094.0
StartCapture=2021-08-24T22:23:49.0399563Z
MidCapture=2021-08-24T22:24:03.2769563Z
EndCapture=2021-08-24T22:24:17.5133277Z
Duration=28.473s
FrameCount=5000
TimeZone=+1.00
 

Any advice appreciated.

 

 

 

 

Edited August 25, 2021 by wornish

[vlaiv]

35 minutes ago, wornish said:

Exposure=0.2470ms

This is way too low.

Planetary imaging is balance between exposure length and freezing the seeing. You want your exposure length to be short enough to freeze the seeing - but not shorter than that since signal strength depends on exposure length and we want each of our subs to have enough signal so that stacking can work and that read noise is not dominant factor.

You can get good results with x20 longer exposures of about 5ms. That is x20 stronger signal. If there is saturation - than back of a bit on gain.

 

 

[wornish]

Tried again last night. This is with 2x Barlow, 12 ms exposure, gain 151.  Think its a bit better but still not happy.

best 5% of 15000 frames.

 

Edited August 26, 2021 by wornish

[vlaiv]

2 hours ago, wornish said:

Tried again last night. This is with 2x Barlow, 12 ms exposure, gain 151.  Think its a bit better but still not happy.

best 5% of 15000 frames.

You don't need barlow and set exposure to ~5ms rather than 12ms.

Also, shoot 30000 frames (go for 3 minute videos, above I've seen that you imaged for only 30s - Duration=28.473s)

[newbie alert]

12 hours ago, vlaiv said:

You don't need barlow and set exposure to ~5ms rather than 12ms.

Also, shoot 30000 frames (go for 3 minute videos, above I've seen that you imaged for only 30s - Duration=28.473s)

3 min subs are far too long for a 9.25 on Jupiter... I'd recommend 45 secs

[vlaiv]

12 minutes ago, newbie alert said:

3 min subs are far too long for a 9.25 on Jupiter... I'd recommend 45 secs

Why do you think that?

Let's do a bit of math to see, shall we?

Jupiter's circumference is about 440,000Km, and it rotates in 9h and 56m - or 35,760s - from that it leads that point on equator that rotates the fastest moves at speed of 440,000Km / 35,760s = ~12.3km/s.

With 9.25" scope being ~235mm has critical sampling rate of 0.22"/px. Single pixel covers 0.22".

Distance to Jupiter is about 600 million kilometers now (or 588 at closest point, but let's go with 600 - nice round number). At that distance 0.22" is equal to 640Km of length.

At above speed, it takes 52s for planet to rotate single pixel at fastest moving point (center of the planet). If we had perfect conditions without atmosphere, any motion blur would be less than single pixel (thus not really visible) even if we did not do alignment points in this time.

Software used for stacking uses alignment points and these alignment points have no trouble aligning features that are even 1-2 arc seconds displaced between subs due to seeing wavefront disturbance (tilt component). This alone can easily compensate for multi minute video - there is no need to derotate even with videos lasting 5-6 minutes (where fastest moving point would move by about 1.3" at most).

To be conservative I recommended half of that, but I happily image for 5 minutes with smaller scopes (0.5"/px resolution for example).

[neil phillips]

22 minutes ago, vlaiv said:

Why do you think that?

Let's do a bit of math to see, shall we?

Jupiter's circumference is about 440,000Km, and it rotates in 9h and 56m - or 35,760s - from that it leads that point on equator that rotates the fastest moves at speed of 440,000Km / 35,760s = ~12.3km/s.

With 9.25" scope being ~235mm has critical sampling rate of 0.22"/px. Single pixel covers 0.22".

Distance to Jupiter is about 600 million kilometers now (or 588 at closest point, but let's go with 600 - nice round number). At that distance 0.22" is equal to 640Km of length.

At above speed, it takes 52s for planet to rotate single pixel at fastest moving point (center of the planet). If we had perfect conditions without atmosphere, any motion blur would be less than single pixel (thus not really visible) even if we did not do alignment points in this time.

Software used for stacking uses alignment points and these alignment points have no trouble aligning features that are even 1-2 arc seconds displaced between subs due to seeing wavefront disturbance (tilt component). This alone can easily compensate for multi minute video - there is no need to derotate even with videos lasting 5-6 minutes (where fastest moving point would move by about 1.3" at most).

To be conservative I recommended half of that, but I happily image for 5 minutes with smaller scopes (0.5"/px resolution for example).

Maths aside kind of with Vlaiv on this. 3 min captures for the most part show little smearing. I personally wouldnt go more than that. I de rotate my 5 min captures. Think i have seen a little smearing around 5 min mark. But it can be variable somewhat. 45 seconds is just losing data. Lots of different opinions on this though. AS/3 Does a good job on 3 min captures. I have found. 

[wornish]

Had a go again last night  but the seeing was terrible.  Couldn't get anything decent out of two runs of 3 mins.

Managed to get three moons in a short 1000 frame, 5ms exposure wide field run.

Below is the best 50 stacked.

Forecast is clear again tonight so not giving in.

 

 

Edited August 27, 2021 by wornish
typo

[wornish]

14 hours ago, vlaiv said:

Why do you think that?

Let's do a bit of math to see, shall we?

Jupiter's circumference is about 440,000Km, and it rotates in 9h and 56m - or 35,760s - from that it leads that point on equator that rotates the fastest moves at speed of 440,000Km / 35,760s = ~12.3km/s.

With 9.25" scope being ~235mm has critical sampling rate of 0.22"/px. Single pixel covers 0.22".

Distance to Jupiter is about 600 million kilometers now (or 588 at closest point, but let's go with 600 - nice round number). At that distance 0.22" is equal to 640Km of length.

At above speed, it takes 52s for planet to rotate single pixel at fastest moving point (center of the planet). If we had perfect conditions without atmosphere, any motion blur would be less than single pixel (thus not really visible) even if we did not do alignment points in this time.

Software used for stacking uses alignment points and these alignment points have no trouble aligning features that are even 1-2 arc seconds displaced between subs due to seeing wavefront disturbance (tilt component). This alone can easily compensate for multi minute video - there is no need to derotate even with videos lasting 5-6 minutes (where fastest moving point would move by about 1.3" at most).

To be conservative I recommended half of that, but I happily image for 5 minutes with smaller scopes (0.5"/px resolution for example).

Thanks for your help.

It is very useful to understand the maths behind planetary imaging.

Can you explain what is meant by critical sampling rate, where does the 0.22"/px figure come from in you post above?

 

 

 

[CaptainKingsmill]

1 hour ago, wornish said:

 but the seeing was terrible. 

You can say that again, I'm close to you in Staffordshire, and it was particularly bad last night.

[wornish]

5 minutes ago, CaptainKingsmill said:

You can say that again, I'm close to you in Staffordshire, and it was particularly bad last night.

Glad it wasn't just me then.

[vlaiv]

1 hour ago, wornish said:

Can you explain what is meant by critical sampling rate, where does the 0.22"/px figure come from in you post above?

Diffraction of light in combination with aperture acts as low pass filter on the image formed by telescope. Single point of light is "distorted" into Airy pattern - which consists out of disk and rings surrounding it.

That is what is called PSF of telescope aperture (point spread function). It has interesting property - it completely removes higher frequency components of the image (think of it as finer detail) - and for that reason we say that telescope can't resolve things beyond certain size. This is commonly referred to as ability to split tight double stars in visual for example.

This highest frequency is known as spatial cutoff frequency for optical system:

https://en.wikipedia.org/wiki/Spatial_cutoff_frequency

This means that image at focal plane of telescope simply does not contain higher frequency components and is band limited.

We can now apply Nyquist-Shannon sampling theorem https://en.wikipedia.org/wiki/Nyquist–Shannon_sampling_theorem

which says that in order to capture band limited signal you need to sample it at twice the highest frequency component present in that signal. Size of pixel dictates sampling rate and also - arc seconds per pixel depends on focal length and pixel size.

When we combine all of these - we get above result. I use green light (~500nm) although in principle you should use 400nm blue as shortest wavelength, but that is the most blurred part of spectrum and very difficult to recover so I choose 500nm as reference wavelength.

To give you exact formulae used:

f_ratio = 2 * pixel_size / wavelength (pixel size and wavelength in same units)

arcsec_per_pixel = 206.3 * pixel_size / focal_length (pixel size in µm and focal length in mm)

 

[newbie alert]

20 hours ago, vlaiv said:

Why do you think that?

Let's do a bit of math to see, shall we?

Jupiter's circumference is about 440,000Km, and it rotates in 9h and 56m - or 35,760s - from that it leads that point on equator that rotates the fastest moves at speed of 440,000Km / 35,760s = ~12.3km/s.

With 9.25" scope being ~235mm has critical sampling rate of 0.22"/px. Single pixel covers 0.22".

Distance to Jupiter is about 600 million kilometers now (or 588 at closest point, but let's go with 600 - nice round number). At that distance 0.22" is equal to 640Km of length.

At above speed, it takes 52s for planet to rotate single pixel at fastest moving point (center of the planet). If we had perfect conditions without atmosphere, any motion blur would be less than single pixel (thus not really visible) even if we did not do alignment points in this time.

Software used for stacking uses alignment points and these alignment points have no trouble aligning features that are even 1-2 arc seconds displaced between subs due to seeing wavefront disturbance (tilt component). This alone can easily compensate for multi minute video - there is no need to derotate even with videos lasting 5-6 minutes (where fastest moving point would move by about 1.3" at most).

To be conservative I recommended half of that, but I happily image for 5 minutes with smaller scopes (0.5"/px resolution for example).

Are you solving on maths or experience?  

Why have you jumped from using a 9.25 which is what you quote as a .22 sampling to a smaller setup as .50

Personally  use 1 min subs on my 8 inch

Think you're looking at it from a deepsky imaging point of view, Jupiter is bright, so you're trying to capture frames of still air.. not dim filaments of structure... So how does it benefit by doing longer subs

I'd contact Christoper go and tell him he's doing it wrong for nearly 20 years..

[vlaiv]

1 hour ago, newbie alert said:

Are you solving on maths or experience? 

On math, experience and comment by Emil Kraaikamp, author of AutoStakkert series of stacking software.

Math suggests what movie length will not suffer from motion blur smear due to planet rotation. This depends on sampling rate (which depends on scope aperture). It is really simple calculation.

I've done some captures of planets and always used 3-4 minutes (or even longer) of captures without derotation, only with AS! software. I've read commend from Emil Kraaikamp that AS!2/3 is capable of handling small rotation of planet - precisely for the reasons I outlined - because it uses alignment points to deal with seeing induced tilt that stretches and distorts image. Such distortion can move alignment point up to 1-2 arc seconds from its original position on successive frames and AS!3 can deal with that without any issues - I don't see why it would not be able to deal with similar shift due to rotation.

1 hour ago, newbie alert said:

Why have you jumped from using a 9.25 which is what you quote as a .22 sampling to a smaller setup as .50

I made connection that if 0.5"/px can use 5-6 minute videos on Jupiter - 0.22"/px can certainly use half of that - 3 minute, as rotation blur grows linearly with time (for small planet rotation angles that discuss here).

0.22"/px is roughly half of 0.5" and 3 minutes is roughly half of 5-6 minutes - makes sense?

1 hour ago, newbie alert said:

Think you're looking at it from a deepsky imaging point of view, Jupiter is bright, so you're trying to capture frames of still air.. not dim filaments of structure... So how does it benefit by doing longer subs

No, I'm not looking at it from deepsky / long exposure point of view. I know precisely what I'm talking about and why.

1 hour ago, newbie alert said:

I'd contact Christoper go and tell him he's doing it wrong for nearly 20 years..

Not sure who Christopher is or why should I be telling him that he's been doing something wrong for past 20 years?

If you are implying that there is a person that is proven planetary imager and that this person said that 30 seconds is limit or something like that, I'd like to remind you that Appeal to authority is form of fallacy:

https://en.wikipedia.org/wiki/Argument_from_authority

Examine arguments presented by this individual and ones presented above and decide based on those.

[skybadger]

It's not longer subs , it's more frames leading to more of higher quality to stack to get critical detail. 

[newbie alert]

13 hours ago, vlaiv said:

 

Just Google Christopher go , where he lives and the impact of that towards his images, yes he uses a c14 but uses max 45 secs on Jupiter, still de-rotate in windupos.. 

Really can't see where you're going with this as I've already outlined that it's not about length of sub lengths,  it's about frames so if you do a 3 min sub or a batch of 4x45 sec you get the same amount of frames

I watch and read alot on planetary and dso imaging and I've yet to come accross anyone that recommends a 3 min sub on Jupiter, so that's a first for me... maybe post your own Jupiter image and change my mind 

[vlaiv]

4 minutes ago, newbie alert said:

Just Google Christopher go , where he lives and the impact of that towards his images, yes he uses a c14 but uses max 45 secs on Jupiter, still de-rotate in windupos.. 

Really can't see where you're going with this as I've already outlined that it's not about length of sub lengths,  it's about frames so if you do a 3 min sub or a batch of 4x45 sec you get the same amount of frames

I watch and read alot on planetary and dso imaging and I've yet to come accross anyone that recommends a 3 min sub on Jupiter, so that's a first for me... maybe post your own Jupiter image and change my mind 

I did not recommend 3 minute sub - I recommended 3 minute of subs (or total duration of video).

But you are absolutely right - there is simple way to asses if one's workflow produces rotation blur or not and at which point - just shoot say 5 minutes of video and then use PIPP to create 30s, 1 minute, 2 minute, ... up to whole 5 minute video (PIPP can export first N frames without processing - effectively "cutting" the video to length).

[newbie alert]

1 hour ago, vlaiv said:

I did not recommend 3 minute sub - I recommended 3 minute of subs (or total duration of video).

But you are absolutely right - there is simple way to asses if one's workflow produces rotation blur or not and at which point - just shoot say 5 minutes of video and then use PIPP to create 30s, 1 minute, 2 minute, ... up to whole 5 minute video (PIPP can export first N frames without processing - effectively "cutting" the video to length).

Oh I think you did.. as there be no point in giving us a maths lesson if the individual subs were say 3x 1min, 4x45, 18x10 secs, and at no point until now you recommend splitting it up into sections even after the OP said he had tried 2 lots of 3 min( good idea thou)..can't see the point of it if it's not relevant to the situation

Christopher Go, just incase you missed him, although you probably already seen his work if you've seen a Hubble image of Jupiter

http://astro.christone.net/

[vlaiv]

2 minutes ago, newbie alert said:

Oh I think you did.. as there be no point in giving us a maths lesson if the individual subs were say 3x 1min, 4x45, 18x10 secs

I'm sorry to have confused you. Here is what I said:

On 26/08/2021 at 11:26, vlaiv said:

You don't need barlow and set exposure to ~5ms rather than 12ms.

Also, shoot 30000 frames (go for 3 minute videos, above I've seen that you imaged for only 30s - Duration=28.473s)

Here you can clearly read that I recommend exposure time set to ~5ms (not in minutes or tens of seconds as you say I did). You can also see that I said - shoot 30000 frames, and to go for 3 minute video instead of 30s one.

You responded to my statement with:

On 26/08/2021 at 23:38, newbie alert said:

3 min subs are far too long for a 9.25 on Jupiter... I'd recommend 45 secs

and I must say that I'm guilty of not properly reading your reply. I assumed that you meant 3 minute video is too long and not 3 minute sub (it really does not make sense to talk about 3 minute subs when we are clearly using millisecond order of magnitude exposures - but it does make sense to talk about 3 minute video vs 30s or 45s one).

I also apologize if my reply containing math explanation sounded condescending. I really did not mean to sound like that - I just wanted to point out that with a bit of math we can estimate size of blur - which combined with the way stacking works - can be used to judge proper video duration.

If we used regular stacking without alignment points - then motion blur due to rotation would become issue after calculated amount of time. Thing is - we use special planetary stacking software as each sub is geometrically distorted as well as blurred due to seeing. This geometric distortion happens because of tilt component of seeing wavefront deformation (which is different for every part of the image).

It is this geometric distortion and its correction that helps us with rotation issues. Single frame is way too short for any measurable rotation to happen - but distortion shift can be larger than total rotation in 3-4 minutes - yet software deals with it.

[newbie alert]

2 minutes ago, vlaiv said:

I'm sorry to have confused you. Here is what I said:

Here you can clearly read that I recommend exposure time set to ~5ms (not in minutes or tens of seconds as you say I did). You can also see that I said - shoot 30000 frames, and to go for 3 minute video instead of 30s one.

You responded to my statement with:

and I must say that I'm guilty of not properly reading your reply. I assumed that you meant 3 minute video is too long and not 3 minute sub (it really does not make sense to talk about 3 minute subs when we are clearly using millisecond order of magnitude exposures - but it does make sense to talk about 3 minute video vs 30s or 45s one).

I also apologize if my reply containing math explanation sounded condescending. I really did not mean to sound like that - I just wanted to point out that with a bit of math we can estimate size of blur - which combined with the way stacking works - can be used to judge proper video duration.

If we used regular stacking without alignment points - then motion blur due to rotation would become issue after calculated amount of time. Thing is - we use special planetary stacking software as each sub is geometrically distorted as well as blurred due to seeing. This geometric distortion happens because of tilt component of seeing wavefront deformation (which is different for every part of the image).

It is this geometric distortion and its correction that helps us with rotation issues. Single frame is way too short for any measurable rotation to happen - but distortion shift can be larger than total rotation in 3-4 minutes - yet software deals with it.

At least we got there in some sort of agreement... I don't find you condescending,  you're a highly intelligent person..far more advanced than most if not all on here in your particular field..   

Christopher realized 20 odd years ago that he lived in a very good area of the world, no jetstream..which is where most of the motion blur comes from.. So it's the same reason that Damien Peach travelled to Barbados to image several times..