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Need advice on sensor size and cooled/uncooled for EAA

astrophotography dso
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#1 seckroaad

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Posted 27 November 2020 - 03:18 PM

I am about to plunge into EAA, having recently discovered its appeal. I just purchased an ASIair, so I am committed (for the time being) to ZWO cameras and the processing available with the ASIair. In looking at the available ZWO cameras (under $1000) I am trying to determine the best first camera choice. Both sensor size and cooling seem to be the major issues, although sensor capacity (i.e., MB) may be important as well. I don't know.

 

My DSO interests range from very small (e.g., Ring Nebula) to quite large (Andromeda), and most common objects (nebulae, clusters, etc.). I like to share my results with others (like my wife and kids), so EAA is appealing to me. I have a home network to which I would export live-stacked images. I have been doing "offline" AP for about 2 years with a Pentax K-7 DSLR, and would like to continue this as well. (The K-7 has no wifi capability but can connect to a laptop via mini HDMI with suitable software.)

 

Equipment: I have an f10 / 200mm SCT (with an f6.3 reducer) and an f6 / 61mm refractor and field flattener. My mount is an AVX. I have not started to autoguide, but I have the equipment for this (50mm scope with an ASI120MM-MINI camera, and the ASIair).

 

Relevant observing environment: Significant light pollution (Bortle 6), but moderate temperatures. I am about 8 miles from the Pacific Coast, 55 miles north of LA. Winter evening temperatures easily drop to 8C at times, so no cooling problem there, I assume. Though summer ocean breezes usually cool things off well, we can experience a weeks long "heat wave" with temperatures up to 22-24C (LOL, I know that would hardly qualify as a heat wave for some).

 

I would like to hear some suggestions or opinions on best camera, as we all pros and cons of things like sensor resolution/size, pixel size, etc. considering my scopes, present equipment, and DSO interests.



#2 StarAlert

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Posted 27 November 2020 - 03:37 PM

Buy the ASI533MC. It's on sale today for $799 from Highpoint. 


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#3 RazvanUnderStars

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Posted 27 November 2020 - 10:41 PM

It depends on your budget as well. Cameras cannot be upgraded to get features you didn't buy initially, you can only sell them and buy others (which is common, granted).

 

A clarification on cooling: it does two things. First, obviously, it cools and therefore it reduces the read noise. It's instructive to check the specs of the camera to see how much it does. The second benefit, perhaps less obvious, is that is stabilizes the temperature. This makes is easier to take matching darks and flats, particularly if you think you'll be doing some A/P as well. Granted, an SCT on a AVX may be a challenging combination, particularly without guiding. Back to cooling: some of the recent CMOS cameras have very low read noise, and given the high light pollution you're facing, that read noise will be insignificant compared to the noise from LP, thus reducing the advantage of cooling. If you think you may travel in the future to darker sites, then cooling becomes more important again.

 

On sensor size: personally I like larger fields, I can see the objects in context, it feels more like an image of "space" as opposed to one of a particular object. Of course, some objects are large as well. I don't think anyone would complain about having a larger FOV, it's just a matter of price.

 

Something I'd recommend reading: Buyer's Guide to ZWO Astronomy Cameras

 

Also, as you probably know already, cameras evolve quickly (look at what we have now: very low noise, ampglow-free cameras at decent prices) so expect that whatever you buy now, you do it for a few years only.


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#4 alphatripleplus

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Posted 28 November 2020 - 09:20 AM

As you have both a short focal length refractor and a C8 with reducer, you already have a range of image scales with any camera you choose. The C8 @ f/4 to f/6.3 will be fine for galaxies and the 61mm f/6 for wide-field emission nebulae. You can certainly start with  a bigger sensor if you want to, but a lot of objects can be framed with a smaller sensor and your two scopes. At this stage, I wouldn't worry about cooling for short sub-exposure EAA.


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#5 seckroaad

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Posted 28 November 2020 - 07:57 PM

It depends on your budget as well. Cameras cannot be upgraded to get features you didn't buy initially, you can only sell them and buy others (which is common, granted).

 

A clarification on cooling: it does two things. First, obviously, it cools and therefore it reduces the read noise. It's instructive to check the specs of the camera to see how much it does. The second benefit, perhaps less obvious, is that is stabilizes the temperature. This makes is easier to take matching darks and flats, particularly if you think you'll be doing some A/P as well. Granted, an SCT on a AVX may be a challenging combination, particularly without guiding. Back to cooling: some of the recent CMOS cameras have very low read noise, and given the high light pollution you're facing, that read noise will be insignificant compared to the noise from LP, thus reducing the advantage of cooling. If you think you may travel in the future to darker sites, then cooling becomes more important again.

 

On sensor size: personally I like larger fields, I can see the objects in context, it feels more like an image of "space" as opposed to one of a particular object. Of course, some objects are large as well. I don't think anyone would complain about having a larger FOV, it's just a matter of price.

 

Something I'd recommend reading: Buyer's Guide to ZWO Astronomy Cameras

 

Also, as you probably know already, cameras evolve quickly (look at what we have now: very low noise, ampglow-free cameras at decent prices) so expect that whatever you buy now, you do it for a few years only.

Thank you for the insights on the function of cooling. As for the link to Agena's guide, I have already been reading it. They also have a guide for EAA that I'm sure you're aware of. Both guides have been very helpful.
 



#6 seckroaad

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Posted 28 November 2020 - 08:06 PM

As you have both a short focal length refractor and a C8 with reducer, you already have a range of image scales with any camera you choose. The C8 @ f/4 to f/6.3 will be fine for galaxies and the 61mm f/6 for wide-field emission nebulae. You can certainly start with  a bigger sensor if you want to, but a lot of objects can be framed with a smaller sensor and your two scopes. At this stage, I wouldn't worry about cooling for short sub-exposure EAA.

Thanks! I have calculated FOV for each camera/scope combination I'm considering to get a feeling for the best single camera for both large and small objects. Of course, I do know that the best practice would be to have more than one camera. But budget may prevent that for now.

 

This question comes up: Is it normal or recommended practice to "enlarge" the image in EAA? In conventional photography I will often enlarge a shot I have taken if the sensor ISO permits without pixelating the image. Can the same be done with the stacked image obtained in EAA? If so, then I would move toward buying a large sensor for the best use of my 360mm scope and plan to enlarge images of small objects taken with the 1280mm scope.



#7 descott12

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Posted 28 November 2020 - 08:20 PM

The answer is pretty simple since your budget will allow for the best. Get the biggest, cooled  sensor you can afford (for the reasons mentioned above).

The 294 and 533 are great choices and you will not be disappointed with either. Availability is the only challenge right now.

 

Note: You can always use a small ROI for small objects but you can't enlarge a small sensor for big ones.

 

Certainly, matching pixel size to your optics does matter, but with EAA, it really isn't that complicated. I have the cooled 294 and it ia s great all around camera. Reports on the 533 are the same. They are both really good choices.


Edited by descott12, 28 November 2020 - 08:21 PM.

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#8 RazvanUnderStars

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Posted 28 November 2020 - 09:00 PM

In daylight photography, the quality of the lens and sensor will determine the resolution. 

In EAA/astrophotography, because the details are so tiny, apart from these two, the quality of the atmosphere will often be the primary limiting factor. Even if the sky is clear (measured by transparency), the atmosphere can be turbulent (measured by seeing) which refracts the light with varying angles. This turbulence, coupled with the longer exposure times, will cause a single point to change brightness and dance around during the exposure, so at the end if becomes a larger disc. Details will become smeared. This will happen with the best optics and the best sensor. So there will be a limit to how much detail you can get, which in turn limits how much you can meaningfully magnify. In practice it's easy: magnify as much or as little as you're happy with, since you can always change it, it's just a display thing. It also depends on the distance between you and the screen.

 

That said, if you search around these forums or any other resource, you'll find two related concepts: undersampling and oversampling. In the first case, the sensor resolution is too low for what the seeing and your specific optical train will provide (the image is subtly pixelated). In the second case, the resolution is too high and the light from a single star (which is a small disc) is spread onto too many pixels, thus reducing what each records. See https://astronomy.to...ccd_suitability for details (the page is equally valid for CMOS cameras).

 

 

This question comes up: Is it normal or recommended practice to "enlarge" the image in EAA? In conventional photography I will often enlarge a shot I have taken if the sensor ISO permits without pixelating the image. Can the same be done with the stacked image obtained in EAA? If so, then I would move toward buying a large sensor for the best use of my 360mm scope and plan to enlarge images of small objects taken with the 1280mm scope.



#9 seckroaad

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Posted 28 November 2020 - 10:03 PM

The answer is pretty simple since your budget will allow for the best. Get the biggest, cooled  sensor you can afford (for the reasons mentioned above).

The 294 and 533 are great choices and you will not be disappointed with either. Availability is the only challenge right now.

 

Note: You can always use a small ROI for small objects but you can't enlarge a small sensor for big ones.

Thanks. But please tell me what is "ROI" and how do you "use" it?



#10 descott12

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Posted 28 November 2020 - 10:09 PM

Thanks. But please tell me what is "ROI" and how do you "use" it?

Region of interest. You can just use part of the sensor.



#11 alphatripleplus

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Posted 28 November 2020 - 10:12 PM

 

 

This question comes up: Is it normal or recommended practice to "enlarge" the image in EAA? In conventional photography I will often enlarge a shot I have taken if the sensor ISO permits without pixelating the image. Can the same be done with the stacked image obtained in EAA?

Aside from the issue of resolution mentioned above, if you are looking to produce a large print, EAA captures typically have more background noise than  astrophotography  (AP) images - much longer AP exposures improve the overall signal to noise ration compared to EAA captures. So I would guess that someone doing imaging is more likely to want to enlarge an image. In EAA the emphasis is on near real time captures, rather than post-processing, but sometimes it is helpful to zoom in to see features if the detail is there. 



#12 seckroaad

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Posted 06 December 2020 - 06:29 PM

Region of interest. You can just use part of the sensor.

When, exactly, do I "use part of the sensor?" I mean, does the ASIAir allow me to "zoom" to a smaller field of view before taking the subs? Or do you mean that the ASIAir takes subs at the full FOV provided by the sensor + scope combination and after the stacked-sub image is downloaded to your tablet you can can zoom into it for finer detail?




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