Asi533 mc pro on a 1000mm Newtonian

[Craig a]

I’m in dire need of a new cooled camera, I’ve been using a modded canon 1100d for a few years now but I want a new cmos, my main interest is galaxys the more obscure the better, I’ve looked at the asi533 but with my 1000mm fl newt it gives me a pixel scale of around 0.77 arc sec now I know the general rule is go between 1-2 arc sec, my question is is it achievable to image at below 1 arc sec or would I be fighting a loosing battle? I don’t want to spend the money on a new camera to be totally dissapointed 

[Adam J]

4 hours ago, Craig a said:

I’m in dire need of a new cooled camera, I’ve been using a modded canon 1100d for a few years now but I want a new cmos, my main interest is galaxys the more obscure the better, I’ve looked at the asi533 but with my 1000mm fl newt it gives me a pixel scale of around 0.77 arc sec now I know the general rule is go between 1-2 arc sec, my question is is it achievable to image at below 1 arc sec or would I be fighting a loosing battle? I don’t want to spend the money on a new camera to be totally dissapointed 

Mostly depends on your local seeing / altitude. But for me less than 1 arcsecond cant be acheived in the UK without DSO lucky imaging.

Adam

[pete_l]

4 hours ago, Craig a said:

 I know the general rule is go between 1-2 arc sec

The "rule" is that in most places atmospheric seeing (turbulence) sets a lower limit on the spot-size of a star of between 1 and 2 arc-sec. However, any connection to the "best" arc-sec per pixel image scale is, at best, rather loose. Personally, I'd be quite happy with 0.7 arc-sec per pixel.

Edited August 17, 2020 by pete_l

[Adam J]

On 17/08/2020 at 19:01, pete_l said:

The "rule" is that in most places atmospheric seeing (turbulence) sets a lower limit on the spot-size of a star of between 1 and 2 arc-sec. However, any connection to the "best" arc-sec per pixel image scale is, at best, rather loose. Personally, I'd be quite happy with 0.7 arc-sec per pixel.

How often would you say you achieve that?  I image at 1.4 per pixel and I can see the effect on FWHM of my stars changing with seeing from night to night. If I am galaxy imaging I sometimes Chuck out whole nights of images as not good enough due to seeing. I should think that 0.7 is workable but maybe only on 1 in 10 nights and I would not image on that basis. Having said that though it's not a reason not to pair a ASI533 with that scope, mostly because in OSC the matric reduced resolution anyway. I just would not kid myself that I would be resolving detail at 0.7 unless I was doing very short exposures. Other locations around the world then it's different but in the UK....I just don't think it's viable to expect to achieve that resolution the vast majority of the time. 

[pete_l]

13 minutes ago, Adam J said:

How often would you say you achieve that? 

Having a seeing of "X" does not mean that your CCD/CMOS arcsec/px has to be the same, Nor does it follow that matching the two will give the best results. Or that having a mismatch will be a disaster. While there may be some sort of theoretical optimal relationship, ISTM the link between the two is not strong. Especially since the chances of any particular star perfectly occupying an entire CCD pixel is extremely small. Most will sit across two or (many) more. And as for dispersed objects (DSOs) the argument weakens considerably as features will be much larger than a star's pinpoint image.

So pretty much any pixel scale, within reason, will give very acceptable results.

Edited August 20, 2020 by pete_l

[vlaiv]

Over sampling is not just about empty resolution - it is about loss of SNR as well.

We all want to get better image in set amount of time or get equal image in shorter time.

Imaging at 0.77"/px vs imaging at for example 1.3"/px - which is much more realistic is deliberately choosing to image for x2.85 less time  - or rather SNR equivalent.

 

[Adam J]

1 hour ago, pete_l said:

Having a seeing of "X" does not mean that your CCD/CMOS arcsec/px has to be the same, Nor does it follow that matching the two will give the best results. Or that having a mismatch will be a disaster. While there may be some sort of theoretical optimal relationship, ISTM the link between the two is not strong. Especially since the chances of any particular star perfectly occupying an entire CCD pixel is extremely small. Most will sit across two or (many) more. And as for dispersed objects (DSOs) the argument weakens considerably as features will be much larger than a star's pinpoint image.

So pretty much any pixel scale, within reason, will give very acceptable results.

I did not say that they have to be matched I just said that seeing normally limits resolved detail even at 1.41 for me and hence I doubt there is consistent benefit to deliberately trying to image at 0.7 in the UK. In spain seeing will be much better.

And vlaiv just beat me to it as I was typing, if you’re not going to see the benefit of higher resolution then you are going to see a reduction in signal to noise ratio as due to the increased sampling less photons are going to fall on each pixel in a given time.

This is why people who jump on the ASI183 with its small pixels as an apparent solution to maintaining sampling in a small aperture refractor never really achieve that in practice as they just end up using more noise reduction negating any potential increase in resolved detail.

Adam

 

 

 

Edited August 20, 2020 by Adam J

[alacant]

On 17/08/2020 at 15:21, Craig a said:

a modded canon 1100d

Hi

How about a better dslr? The newer models with the 18mp sensor are streets ahead of the 1100.

Cheers

[pete_l]

4 hours ago, vlaiv said:

Imaging at 0.77"/px vs imaging at for example 1.3"/px - which is much more realistic is deliberately choosing to image for x2.85 less time  - or rather SNR equivalent.

That makes the assumption that a star of 1.3 arc seconds dispersion is exactly resolved on a single sensor pixel of the same size. That is extremely unlikely to happen and any star's image will almost always be shared between several adjacent pixels. Hence the idealised SNR from the calculation will rarely be obtained. And then, only for a small proportion of stars since they are randomly positioned in the sky.

When you add to that the random tracking errors of the mount, there will never be a case where the textbook calculations are met.

 

Simply put: the difference between theory and practice in practice is greater than the difference between theory and practice in theory

Edited August 20, 2020 by pete_l

[vlaiv]

12 minutes ago, pete_l said:

That makes the assumption that a star of 1.3 arc seconds dispersion is exactly resolved on a single sensor pixel of the same size. That is extremely unlikely to happen and any star's image will almost always be shared between several adjacent pixels. Hence the idealised SNR from the calculation will rarely be obtained. And then, only for a small proportion of stars since they are randomly positioned in the sky.

When you add to that the random tracking errors of the mount, there will never be a case where the textbook calculations are met.

 

Simply put: the difference between theory and practice in practice is greater than the difference between theory and practice in theory

No it does not make that assumption.

Imagine you have certain sampling rate - and you just simply split each pixel in grid 2x2.

Regardless of how many pixels star or nebula initially covered - in this scenario every new pixel will have 1/4 of the photons of original pixel. Smaller pixels - less photons captured. Stars / nebulae - all the same.

[Craig a]

To get to that 1.3 with my scope I would have to have a cam with over 6um pixels! I don’t know any reasonably price cooled cmos with pixels that big or am I wrong? The reason for thinking about the 533 is the low read noise and deep wells plus it’s nicely priced, being a new dad money is a big factor now and spending 1500-2000 on a new cam is a bitter pill to swallow when I’ve got a new baby, I have also looked at the asi294mc pro that would give me 0.96 arc sec per pixel, still not ideal but I really carnt afford to get a new scope aswell to match these new cmos with smaller pixels, sorry I should of mentioned the criteria in my first post, also I’ve heard people having a terrible time with uneven chip cooling on the 294 in the past, is that still something that is a problem or has that been fixed?

[Adam J]

1 hour ago, Craig a said:

To get to that 1.3 with my scope I would have to have a cam with over 6um pixels! I don’t know any reasonably price cooled cmos with pixels that big or am I wrong? The reason for thinking about the 533 is the low read noise and deep wells plus it’s nicely priced, being a new dad money is a big factor now and spending 1500-2000 on a new cam is a bitter pill to swallow when I’ve got a new baby, I have also looked at the asi294mc pro that would give me 0.96 arc sec per pixel, still not ideal but I really carnt afford to get a new scope aswell to match these new cmos with smaller pixels, sorry I should of mentioned the criteria in my first post, also I’ve heard people having a terrible time with uneven chip cooling on the 294 in the past, is that still something that is a problem or has that been fixed?

However, for conventional imaging you are correct there is no cheap CMOS sensor with big pixels. There is the ASI2400MC Pro full frame that was recently announced but its not cheap. Just because you are over sampled does not mean you can’t use a 533 and take a great image with it, its just not optimal, you can resample in software. I think the point most people are making is just don’t expect to achieve 0.7. 

You are 100% correct about the chip cooling issues on 294 so I would not go that way.

Have you thought about a ASI071MC Pro? It will also give you a much nicer FOV at your focal length. Or for that matter the cheaper (and possibly slightly better) QHY168c. QE is lower and read noise higher but the pixel area is almost double so it makes up for that and you end up with a larger FOV.

https://www.modernastronomy.com/shop/cameras/cooled-ccd/qhy-cooled-ccd-cameras/qhy168c/

https://www.astrobin.com/full/uy18rl/0/

https://www.astrobin.com/full/nvngqu/0/

https://www.astrobin.com/full/nxqf5h/0/

Your original question was "my question is is it achievable to image at below 1 arc sec or would I be fighting a loosing battle?" I took that to mean guiding and seeing, in which case yes you are probably fighting a losing batter trying to achieve that resolution in the UK. But that’s not to say the 533 will not work at all, it is just not optimal at that focal length with UK seeing.

Another option is to ditch the 200mm F5 Newtonian and go with a 130PDS or a 150PDS and the 533. The 130PDS is only £180 new after all you could buy one for the second hand sale of the 1000mm scope you currently have.... thats what I would do.

Might be cheaper to do that than go with the larger pixels and sensor and it will be easier to guide also.

But totally on the flip side, if its small galaxies you want then maybe you are willing to wait for that one night in ten when you will get the seeing to make the 0.77 scale worth it? Only you know that.

Adam

 

 

Edited August 20, 2020 by Adam J

[alacant]

10 minutes ago, Adam J said:

a cam with over 6um pixels

With the renewed interest in multistar guiding, you may well get away with smaller.  Remember to look at the images though, not the numbers!

Cheers

[Adam J]

2 minutes ago, alacant said:

With the renewed interest in multistar guiding, you may well get away with smaller.  Remember to look at the images though, not the numbers!

Cheers

I thought that multi star guiding helped to stop you from "chasing the seeing" as you are averaging the motion of multiple stars, but it cant actually remove the effect of seeing on the image itself. Hence it helps you guide but will not actually improve your FWHM that much.

Adam

[alacant]

1 minute ago, Adam J said:

will not actually improve your FWHM

Hi

It does here. Try it.

 

[Adam J]

1 minute ago, alacant said:

Hi

It does here. Try it.

 

I get the impression there was supposed to be a link in there somewhere?

[Craig a]

33 minutes ago, Adam J said:

Or for that matter the cheaper (and possibly slightly better) QHY168c.

Yes that could be an option, I would find it hard to go down to a smaller sensor if I did go with the 533 as I’m coming from a dslr, an 1100d which is ancient now in camera terms with a pretty poor QE of about 35% I think

[mikeyj1]

I have to say imaging with a DSLR on a 1000mm or in my case 1200mm is perfect.  I've been trying out a QSi6120 mono (3.1um pixels), and i find that binning 2x2 is better than 1x1 for star shape and bloat. 

Personally, i have hankered after the QHY8 or the QHY10 as a good upgrade from DSLR, as they still have the same format sensor but good cooling.  i know they are getting on a bit, but that D5100 sensor is still really v good

hope that doesn't add to your confusion...! 

Mike

[vlaiv]

There are a lot of options out there that will give you what you want.

First is to figure out FOV and sampling rate.

Since you have 8" scope with 1000mm FL, I would say that your sampling rate should ideally be around 1.2"/px. If you are happy with ASI533 FOV, then let's examine possible candidates, all similarly priced.

ASI533 with 3.76um pixels and sampling rate of 0.78"/px. Since this is color camera, your sampling rate is actually double that - 1.55"/px but your pixel sensitivity is like when sampling at 0.78"/px (except that you are sampling 1 red, 1 blue and 2x green images at the same time - confusing, right? ). Use super pixel mode for debayering and you'll get 1500x1500 pixel camera with 1.55"/px sampling rate.

Next contender is ASI183 - almost same diagonal so similar FOV

It is sampling at 0.5"/px or 1"/px in reality. You can bin it in software to get 2"/px. This will make it be 1374px  x 918px equivalent camera, but you'll get rather good collecting surface of 1"/px at 200mm aperture.

I would not shy away from ASI294. I think it is quite decent camera from what I've seen - once configured properly.

It will sample at 0.96"/px or in reality at 1.91"/px when doing super pixel mode. It will collect as much light per pixel as ASI183 when super pixel debayered and then binned x2 but it will produce images that are 2072px x 1411px.

To my mind - that is probably the best option in terms of image size and collecting power and sampling resolution.

 

How about going for ASI183 mono version? You don't have to invest in filters and filter wheel yet if you can be happy with monochromatic images. After all, you said that you are after obscured galaxies (more obscured the better in fact). Those will be low SNR affair and I think you can sacrifice the color in that case for good SNR.

With ASI183 mono version, you can "have your cake and eat it too".  With bin x3, you'll have 1.49"/px sampling rate and this will translate into full light gathering area for whole spectrum.

 

[Adam J]

14 minutes ago, vlaiv said:

I would not shy away from ASI294. I think it is quite decent camera from what I've seen - once configured properly.

Not sure what you mean by configured properly?

The issue with that sensor is calibration is very difficult due to ambient temperature changes between dark frames and light frames resulting in small regional variations in chip temperature. Hence it will only calibrate correctly if you are able to take darks at the same ambient temperature as the lights or at least close to the same, despite the regulated cooling. Basically only a small area of the chip is in contact with the cooler due to the pin layout on the rear.

You can see it in deep images of galaxies when a large stretch has been applied you get a pattern in the background that is essentially the contract pads between the thermal cooling and the back side of the chip.

You never see it in nebula shots as its buried under the signal....but with galaxy imaging it can be quite nasty. Hence I would avoid it and go for either the 533 or the 071.

Well actually I would probably go with a ATIK414 mono is this application but thats a different argument all together.

Adam

 

 

 

Edited August 20, 2020 by Adam J

[Adam J]

46 minutes ago, Craig a said:

Yes that could be an option, I would find it hard to go down to a smaller sensor if I did go with the 533 as I’m coming from a dslr, an 1100d which is ancient now in camera terms with a pretty poor QE of about 35% I think

QE is said to be about 50% on the IMX071 and the read noise is almost half that of the 1100D. Add cooling and it would be a very significant upgrade over the 1100D. You dont need the FOV for small galaxies but you may want to image other things from time to time.

Edited August 20, 2020 by Adam J

[vlaiv]

2 minutes ago, Adam J said:

Not sure what you mean by configured properly?

The issue with that sensor is calibration is very difficult due to ambient temperature changes between dark frames and light frames resulting in small regional veriations in chip temperature. Hence it will only calibrate correctly if you are able to take darks at the same ambient temperature as the lights or at least close to the same.

You can see it in deep images of galaxies when a large stretch has been applied you get a pattern in the background that is essentially the contract pads between the thermal cooling and the back side of the chip.

You never see it in nebula shots as its burried under the signal....but with galaxy imaging it can be quite nasty. Hence I would avoid it and go for either the 533 or the 071.

Well actually I would probably go with a ATIK414 mono is this application but thats a different argument all together.

Adam

 

Have you actually examined set of darks made at different ambient temperature and same set point temperature?

What I'm referring to is proper offset value being set. Too low offset will cause clipping in darks and as a consequence - light patches in calibrated lights (in places where darks should have been darker but have been clipped).

I personally did not work with said camera but have had PM discussion with one owner and walked them thru proper generation of calibration files and they were rather happy with results.

[Craig a]

16 minutes ago, vlaiv said:

There are a lot of options out there that will give you what you want.

First is to figure out FOV and sampling rate.

Since you have 8" scope with 1000mm FL, I would say that your sampling rate should ideally be around 1.2"/px. If you are happy with ASI533 FOV, then let's examine possible candidates, all similarly priced.

ASI533 with 3.76um pixels and sampling rate of 0.78"/px. Since this is color camera, your sampling rate is actually double that - 1.55"/px but your pixel sensitivity is like when sampling at 0.78"/px (except that you are sampling 1 red, 1 blue and 2x green images at the same time - confusing, right? ). Use super pixel mode for debayering and you'll get 1500x1500 pixel camera with 1.55"/px sampling rate.

Next contender is ASI183 - almost same diagonal so similar FOV

It is sampling at 0.5"/px or 1"/px in reality. You can bin it in software to get 2"/px. This will make it be 1374px  x 918px equivalent camera, but you'll get rather good collecting surface of 1"/px at 200mm aperture.

I would not shy away from ASI294. I think it is quite decent camera from what I've seen - once configured properly.

It will sample at 0.96"/px or in reality at 1.91"/px when doing super pixel mode. It will collect as much light per pixel as ASI183 when super pixel debayered and then binned x2 but it will produce images that are 2072px x 1411px.

To my mind - that is probably the best option in terms of image size and collecting power and sampling resolution.

 

How about going for ASI183 mono version? You don't have to invest in filters and filter wheel yet if you can be happy with monochromatic images. After all, you said that you are after obscured galaxies (more obscured the better in fact). Those will be low SNR affair and I think you can sacrifice the color in that case for good SNR.

With ASI183 mono version, you can "have your cake and eat it too".  With bin x3, you'll have 1.49"/px sampling rate and this will translate into full light gathering area for whole spectrum.

 

My scope is a 10inch 1000mm f4

[vlaiv]

Just now, Craig a said:

My scope is a 10inch 1000mm f4

Won't make much difference to FOV - 1000FL in either case. 10" aperture will simply collect more light and will be more demanding on collimation and field correction - both fully illuminated field and fully corrected field.

[Adam J]

10 minutes ago, vlaiv said:

Have you actually examined set of darks made at different ambient temperature and same set point temperature?

What I'm referring to is proper offset value being set. Too low offset will cause clipping in darks and as a consequence - light patches in calibrated lights (in places where darks should have been darker but have been clipped).

I personally did not work with said camera but have had PM discussion with one owner and walked them thru proper generation of calibration files and they were rather happy with results.

No but there is a significant thread on the issue on cloudy nights where some experianced imagers tried lots of different things to try and get the background to calibrate properly and failed.

https://www.cloudynights.com/topic/596025-zwo-asi294-mc-pro/page-7

I dont think its a problem with clipping to be honest.

It only shows when you try and go really deep. So most less experianced imagers will not experiance it.

From the lack of star burst amp glow you can see its been calibrated "correctly".

If you have a read let me know what you think.

Adam

Edited August 20, 2020 by Adam J