Which Dedicated Astro Camera - Help Needed :)

[Stuf1978]

Hi All,

Apologies for the long post and I’m sure this has probably been covered numerous times but I’m trying to get it clear in my head (I'm still relatively new to this so it’s taking me a while to get my head around it).

I’m looking to upgrade my dslr (450D mod) to a cooled astro cam in the next few months. I’m currently imaging with a SW ED72 with OVL flattener (so 420mm FL) and a range of Canon EF lenses ranging  from 24mm up to 300mm focal length. These are all used on a SW HEQ5 Pro running EQMOD and APT so image capture will remain the same. I’ll probably be going down the OSC route as I like the simplicity of it, and it isn’t such a massive change from what I’m currently doing. I’m already using a ZWO ASI120MM Mini for guiding so was looking at sticking with ZWO for compatibility reasons  as I like the idea of being able to connect the guide camera to the main imaging camera to simplify cable management (not sure this could be done if I used a different brand of camera?). At some point I also want to add a couple more OTA’s to my collection for more focal length (e.g. SW ED80) and more widefield (e.g. Redcat) in order to be less reliant on camera lenses.

I was just going to order the ZWO ASI294MC Pro and be done with it as the field of view isn’t too dissimilar to my current dslr which I like. However, I then got reading about under sampling/oversampling and this got me concerned over image quality at short focal lengths. So, I started looking at other options (183 and 533 MC Pro).

As far as I can see these will still under sample at short focal lengths but are likely to fair better than the 294MC Pro. However, I don’t like the square sensor on the 533MC Pro and the FOV is too narrow for my liking on the 183MC Pro. I’ve tabulated all my options and simulated the FOV and keep coming back to the 294MC Pro. I guess what I’m asking is how much impact will under sampling on the 294 have on widefield image quality (24-200mm). It should fare fine if I add the scopes outlined above to my collection. Part of me thinks I’m just overthinking this as all options will fare better than my current camera and I’m fairly happy with the images it can produce.

So, if anyone else has had this predicament please let me know what you decided on 😊

Thanks,

Stu

Edited October 30, 2020 by Stuf1978

[vlaiv]

First things first - don't worry about under sampling.

Two reasons for that - first is that under sampling is not a bad thing in itself. It is just a working resolution and lower working resolution just means wider field of view (over sampling is a bad thing as you loose SNR and gain nothing in return).

Second thing - you are worrying about under sampling with camera lens. You should not. Camera lens are not diffraction limited and star image that they are producing is much larger than aperture would suggest.

To prove my point, here is measurement of Samyang 85mm F/1.4 lens that I did with artificial star:

No filter at F/1.4 - Red: 2.66, Green: 2.48, Blue: 2.30
No filter at F/2.0 - Red: 3.82, Green: 2.28, Blue: 2.42
No filter at F/2.8 - Red: 2.53, Green: 2.36, Blue: 2.31
No filter at F/4.0 - Red: 2.24, Green: 2.27, Blue: 2.29

Values that you see are FWHM of different channels expressed in pixels and pixel size is 4.8µm.

Best of these values are around 2.3px or if we convert that into microns - 11.04µm. FWHM of 11.04µm requires pixel size of 6.9µm to be properly sampled.

In the case of this lens, and probably most of other lenses (don't think that other lens are much better than this one - this is pretty good/sharp lens) - it is neither seeing nor tracking that produces blur, it is lens itself. They are far, far from diffraction limited optics.

Btw, this is what star looks like at F/1.4

And this is what it looks like at F/2.8 (and above sampling with pixel size of 4.8µm):

While slightly over sampled (yes indeed even at F/2.8, 4.8µm pixel size is over sampling rather than under sampling), this star looks rather nice. Going further to F/4 will not make much of a difference:

Bottom line - don't worry about under sampling, if you are happy with FOV for your intended targets at focal lengths that you work with - go for ASI294. It has best size/£ ratio and it is very decent performing camera.

[Stuf1978]

9 minutes ago, vlaiv said:

First things first - don't worry about under sampling.

Two reasons for that - first is that under sampling is not a bad thing in itself. It is just a working resolution and lower working resolution just means wider field of view (over sampling is a bad thing as you loose SNR and gain nothing in return).

Second thing - you are worrying about under sampling with camera lens. You should not. Camera lens are not diffraction limited and star image that they are producing is much larger than aperture would suggest.

To prove my point, here is measurement of Samyang 85mm F/1.4 lens that I did with artificial star:

No filter at F/1.4 - Red: 2.66, Green: 2.48, Blue: 2.30
No filter at F/2.0 - Red: 3.82, Green: 2.28, Blue: 2.42
No filter at F/2.8 - Red: 2.53, Green: 2.36, Blue: 2.31
No filter at F/4.0 - Red: 2.24, Green: 2.27, Blue: 2.29

Values that you see are FWHM of different channels expressed in pixels and pixel size is 4.8µm.

Best of these values are around 2.3px or if we convert that into microns - 11.04µm. FWHM of 11.04µm requires pixel size of 6.9µm to be properly sampled.

In the case of this lens, and probably most of other lenses (don't think that other lens are much better than this one - this is pretty good/sharp lens) - it is neither seeing nor tracking that produces blur, it is lens itself. They are far, far from diffraction limited optics.

Btw, this is what star looks like at F/1.4

And this is what it looks like at F/2.8 (and above sampling with pixel size of 4.8µm):

While slightly over sampled (yes indeed even at F/2.8, 4.8µm pixel size is over sampling rather than under sampling), this star looks rather nice. Going further to F/4 will not make much of a difference:

Bottom line - don't worry about under sampling, if you are happy with FOV for your intended targets at focal lengths that you work with - go for ASI294. It has best size/£ ratio and it is very decent performing camera.

Wow!! Thank you, that's great information  

It confirms my suspicion that I was procrastinating over nothing and that the ASI 294MC Pro is going to be a massive improvement over my 450D. 

[TerryMcK]

I have no complaints with my ZWO ASI183MC and ASI183MM with the apertures/focal lengths I use. I too don't like the square format of the 533 despite its promise of zero amp glow.

One thing to bear in mind with the 183 is the amp glow but it can be calibrated out completely. Also keep the gain down to default 111 or even 53 and it is more than sensitive enough. The 183's from ZWO also have AR coatings on the aperture windows so you don't get any internal reflections.

[Stuf1978]

14 minutes ago, TerryMcK said:

I have no complaints with my ZWO ASI183MC and ASI183MM with the apertures/focal lengths I use. I too don't like the square format of the 533 despite its promise of zero amp glow.

One thing to bear in mind with the 183 is the amp glow but it can be calibrated out completely. Also keep the gain down to default 111 or even 53 and it is more than sensitive enough. The 183's from ZWO also have AR coatings on the aperture windows so you don't get any internal reflections.

Thanks that's good to know, the 183 FOV looks a little tight for my liking which would mean I'd have to resort to mosaics for larger targets. I've also read about amp glow on the 294MC Pro, but good calibration frames make it a bit of a non-issue. 

I think in a money no object world I'd have a range of cameras to cover all eventualities 😆

[vlaiv]

With cooled cameras amp glow is really not an issue.

Both cameras that I use have amp glow in one form or another. Here is for example very stretched dark frame from ASI178mcc (used for above test of Samyang lens - but not with native 2.4µm pixel size but rather in super pixel debayer mode):

And I get very decent results with this camera - have look at what I recently took with above mentioned Samyang lens:

You'll see that image is still a bit blurry / not as sharp as it could be - that is mostly because of the fact that I used lens at F/2 (wanted to do decent image in just one hour from strong light pollution - I probably should have gone for two hours and F/2.8 instead) and that even with 4.8um pixel size - image is over sampled.

[Adam J]

2 hours ago, Stuf1978 said:

 started looking at other options (183 and 533 MC Pro)

I see better images from the 533 than the 294 people talk about the images being easier to process. That's why I would go for it not because of sampling vlaiv is correct lenses are not likely to be diffraction limited. The only other consideration is FOV and that depends on what you want to image. 

Edited October 30, 2020 by Adam J

[Stuf1978]

48 minutes ago, Adam J said:

I see better images from the 533 than the 294 people talk about the images being easier to process. That's why I would go for it not because of sampling vlaiv is correct lenses are not likely to be diffraction limited. The only other consideration is FOV and that depends on what you want to image. 

Double quoted, see below  

55 minutes ago, vlaiv said:

With cooled cameras amp glow is really not an issue.

Both cameras that I use have amp glow in one form or another. Here is for example very stretched dark frame from ASI178mcc (used for above test of Samyang lens - but not with native 2.4µm pixel size but rather in super pixel debayer mode):

And I get very decent results with this camera - have look at what I recently took with above mentioned Samyang lens:

You'll see that image is still a bit blurry / not as sharp as it could be - that is mostly because of the fact that I used lens at F/2 (wanted to do decent image in just one hour from strong light pollution - I probably should have gone for two hours and F/2.8 instead) and that even with 4.8um pixel size - image is over sampled.

Thanks, yeah it's a non issue with the correct calibration frames

48 minutes ago, Adam J said:

I see better images from the 533 than the 294 people talk about the images being easier to process. That's why I would go for it not because of sampling vlaiv is correct lenses are not likely to be diffraction limited. The only other consideration is FOV and that depends on what you want to image. 

Yeah I've seen some very nice images taken with the 533 but that can also be said for the 294. I'm just not keen on that square sensor, you've got way more framing options with a rectangular sensor and the 294 fits in with what I want to image much better. In what way are the 533 images easier to process?

Edited October 30, 2020 by Stuf1978

[vlaiv]

2 minutes ago, Stuf1978 said:

In what way are the 533 images easier to process?

@Adam J I'm also interested in your view on that one.

[wimvb]

22 minutes ago, Stuf1978 said:

I'm just not keen on that square sensor, you've got way more framing options with a rectangular sensor

With a square sensor you don’t need to rotate your camera, you just crop to the aspect ratio you want. Much easier, in my opinion.

[vlaiv]

2 minutes ago, wimvb said:

With a square sensor you don’t need to rotate your camera, you just crop to the aspect ratio you want. Much easier, in my opinion.

In a "sport" that aims to make every photon count, you want to crop your sensor and throw away captured photons?

Sacrilege!

[wimvb]

Just now, vlaiv said:

In a "sport" that aims to make every photon count, you want to crop your sensor and throw away captured photons?

Sacrilege!

If only there were cameras with round sensors, and desktop software with round windows/workspaces. 🧐

[vlaiv]

5 minutes ago, wimvb said:

If only there were cameras with round sensors, and desktop software with round windows/workspaces. 🧐

Not only round, but curved as well!

[Stuf1978]

14 minutes ago, wimvb said:

With a square sensor you don’t need to rotate your camera, you just crop to the aspect ratio you want. Much easier, in my opinion.

That may be true, but you also have less space to play with especially for bigger targets

[Adam J]

1 hour ago, vlaiv said:

@Adam J I'm also interested in your view on that one.

Probably better signal to noise and I am told that often you don't need to bother with calibration frames (not even darks) if you dither the 533. I know two people with both cameras (533 and 294) and they both agree that it seems easier to get I nicer results out of the 533. I'll try to get them to comment here but they mainly post on Facebook. I have nothing against the 294 really dont but if you don't feel you need the fov for the targets and your setup the 533 is the better sensor. There is also a well known calibration issue with the 294 reported by many on cloudy nights concerning blochie backgrounds that can't be calibrated out. 

This chap says the same thing. 533 better except for FOV. 

 

Discussion of calibration here: 

https://www.cloudynights.com/topic/636301-asi294mc-calibration-–-testing-notes-thoughts-and-opinions/

But again if you want the FOV it's the 294 or pay for the 2600. 

Adam

 

Edited October 30, 2020 by Adam J

[vlaiv]

39 minutes ago, Adam J said:

Discussion of calibration here: 

https://www.cloudynights.com/topic/636301-asi294mc-calibration-–-testing-notes-thoughts-and-opinions/

This was very interesting read and I'll need to try something mentioned in that thread. I never tried to take few seconds of pause between exposures, but I did notice case where that might be useful thing to try.

Sometimes there is rather strange thing happening with darks - some of them have higher mean value. Others have different standard deviation  - as if more noise is there (these are not calibrated so it could as well be some signal/pattern producing higher standard deviation).

Maybe this would not happen with few seconds pause between subs. Camera in question is ASI178,

[Stuf1978]

6 hours ago, Adam J said:

Probably better signal to noise and I am told that often you don't need to bother with calibration frames (not even darks) if you dither the 533. I know two people with both cameras (533 and 294) and they both agree that it seems easier to get I nicer results out of the 533. I'll try to get them to comment here but they mainly post on Facebook. I have nothing against the 294 really dont but if you don't feel you need the fov for the targets and your setup the 533 is the better sensor. There is also a well known calibration issue with the 294 reported by many on cloudy nights concerning blochie backgrounds that can't be calibrated out. 

This chap says the same thing. 533 better except for FOV. 

 

Discussion of calibration here: 

https://www.cloudynights.com/topic/636301-asi294mc-calibration-–-testing-notes-thoughts-and-opinions/

But again if you want the FOV it's the 294 or pay for the 2600. 

Adam

 

Thank you, just watched that review and read through the CN thread. There is a lot of food for thought in there. The 533 does sound very very good especially as I do most of my imaging from a bortle 8 zone. Sadly the FOV is a deal breaker for me.  Additionally it seems a lot of the issues with the 294 just need careful consideration over the calibration frames. Maybe I should just bite the bullet and go for the 2600MC Pro...... but for that price I could have a full mono set up with all the filters needed 🤪

Edited October 30, 2020 by Stuf1978

[Adam J]

59 minutes ago, Stuf1978 said:

Thank you, just watched that review and read through the CN thread. There is a lot of food for thought in there. The 533 does sound very very good especially as I do most of my imaging from a bortle 8 zone. Sadly the FOV is a deal breaker for me.  Additionally it seems a lot of the issues with the 294 just need careful consideration over the calibration frames. Maybe I should just bite the bullet and go for the 2600MC Pro...... but for that price I could have a full mono set up with all the filters needed 🤪

In class 8 you should be going mono and focusing on narrow band imaging. The new duel channel filters like L-Extream are great, but in your conditions mono will still be much better.

Adam

[Stuf1978]

2 hours ago, Adam J said:

In class 8 you should be going mono and focusing on narrow band imaging. The new duel channel filters like L-Extream are great, but in your conditions mono will still be much better.

Adam

Mono is probably the right way to go but the simplicity of OSC is hard to ignore. I'm sure the mono v osc debate has been discussed to death but it's still a difficult decision to make. Do I stick with OSC and get up and running straight away or go mono and have a couple of months of pain but with much better image quality in the long run. This is hurting my head 😂

[gorann]

If you go for a OSC and have the budget, then, from your list, the ASI2600MC should be you choice and a good match to your lenses. It is just an amazing camera with zero amp glow, very light sensitive, very low noise, and a large enough sensor. I have been using one this autumn and Iove it (I do have other ASI cameras to compare with). You can click on my Astrobin to see some of the pics from this autumn.

[Stuf1978]

1 hour ago, gorann said:

If you go for a OSC and have the budget, then, from your list, the ASI2600MC should be you choice and a good match to your lenses. It is just an amazing camera with zero amp glow, very light sensitive, very low noise, and a large enough sensor. I have been using one this autumn and Iove it (I do have other ASI cameras to compare with). You can click on my Astrobin to see some of the pics from this autumn.

Wow those are some very very nice images, it looks like an impressive bit of kit 😲.

It's on my list but it's very expensive so I would likely have to wait a bit longer for that one and then justify whether it's worth double the 294MC Pro. 

[CCD-Freak]

I went with the ASI-533MCP and have not regretted it.   Low noise, No amp glow, deep well depth etc...what's not to like.  I even like the square sensor because it frames most objects without a lot wasted real estate.  The attached M42 image is only 60 x 1 minute.

John Love
CCD-Freak
WD5IKX

[Stuf1978]

1 hour ago, CCD-Freak said:

I went with the ASI-533MCP and have not regretted it.   Low noise, No amp glow, deep well depth etc...what's not to like.  I even like the square sensor because it frames most objects without a lot wasted real estate.  The attached M42 image is only 60 x 1 minute.

John Love
CCD-Freak
WD5IKX

Must admit that's a very nice image 👍

[DaveS]

When I moved from a DSLR I was living in West London and went straight to mono, didn't even pause to consider OSC, just a no-brainer.

[2STAR]

On 30/10/2020 at 13:14, Stuf1978 said:

Thanks that's good to know, the 183 FOV looks a little tight for my liking which would mean I'd have to resort to mosaics for larger targets. I've also read about amp glow on the 294MC Pro, but good calibration frames make it a bit of a non-issue. 

I think in a money no object world I'd have a range of cameras to cover all eventualities 😆

No Amp glow on the 533, and the SQ sensor is no issue either.