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Comparison Between DSLR and ASI1600mm-Cool Images

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#26 Peter10

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Posted 19 September 2016 - 08:47 PM

Thanks for all of the feedback.  Based on your responses, I may have jumped to incorrect conclusions on the 12-bit A/D converter.  With low read noise, the technique may be to collect a large number of shorter duration subs that are summed in 32-bit space.  It seems that this would mitigate concerns over the camera's small bit depth.

 

Peter



#27 whwang

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Posted 19 September 2016 - 09:34 PM

Hi Wei-Hao, 

 

What you wrote here is very interesting for my case, but I don't understand your explanations. Could you please elaborate?

I am living in a highly polluted environment and I would like to determine the best solution to image in these conditions. 

 

Thank you, 

 

Hi Nicolas,

 

Under highly polluted sky, the first thing to consider is a light pollution filter or even narrow-band filters.

 

In terms of exposure strategy, the key is always getting enough exposure so the sky background in your image is much higher than the readout noise.  Once this is satisfied, there will be no difference between stacking 100 1-minute exposures and stacking 10 10-minute exposures.  The former will take more disk space and more processing time, but will give you more usable dynamical range as I explained in my previous post.  And the tracking will be easier too.  The latter is the opposite, taking less disk space and processing time, but also giving you less dynamical range.

 

You can try to find a tool that can linearly convert the raw file and display pixel values.  In a 16 bit TIFF file, the saturation level should be 65535 (will be shown as 255 in Photoshop).  However, since most DSLRs have 14 bit AD conversion, the largest pixel value you will see in a linearly converted DSLR raw file will then be only 16383 (64 in Photoshop).  Suppose you use an ISO that roughly gives a unity gain, which is usually somewhere between ISO 400 and ISO 1600 (say, ISO 800) on most DSLRs.  Then any exposure time that can give you a sky background that is 100 to 200 above the bias level should be good enough.  You won't need to exposure any longer in a sub.

 

I hope this helps.

 

Cheers,

Wei-Hao


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#28 JukkaP

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Posted 20 September 2016 - 01:49 AM

Awsome information Wei-Hao. But is that correct only for the sky colour or also how we see the imaging object in the end picture?

Lets say we imagine ngc7000 in medium light polution zone. Then take 10x10min exposure vs 100x1min exposure. Should the nebula have more dynamic range in the 1min stack or in 10min stack?

#29 whwang

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Posted 20 September 2016 - 02:06 AM

Awsome information Wei-Hao. But is that correct only for the sky colour or also how we see the imaging object in the end picture?

Lets say we imagine ngc7000 in medium light polution zone. Then take 10x10min exposure vs 100x1min exposure. Should the nebula have more dynamic range in the 1min stack or in 10min stack?

Hi, I would say the 1min stack will have less saturated stars.  Most nebulas (including NGC7000) are faint.  The compression of dynamical range (either in the 100*1 case or 10*10 case) should not affect such nebulas too much.  Of course there are exceptions.  For bright nebulas like M42, M31, M8, M20, M16, M17, and star clusters, their cores will show much better in the 100*1 stack than the 10*10 stack.



#30 bobzeq25

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Posted 20 September 2016 - 09:27 AM

 

 

 Then any exposure time that can give you a sky background that is 100 to 200 above the bias level should be good enough.  You won't need to exposure any longer in a sub.

 


 

Just making sure I understand.  What you're saying is, if your bias is 600 ADU, you're wanting the lefthand edge (where it falls to zero) of the skyfog peak to be at 700-800 ADU?



#31 whwang

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Posted 20 September 2016 - 10:43 AM

Just making sure I understand.  What you're saying is, if your bias is 600 ADU, you're wanting the lefthand edge (where it falls to zero) of the skyfog peak to be at 700-800 ADU?

 

Right, assuming you are using ISO 400 to 1600.  That's the minimum requirement though.  You can go higher, but not lower, and it's not necessary to go much higher.


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#32 Poochpa

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Posted 22 September 2016 - 02:58 PM

I've been imaging with Canon APS-C DSLRs for about 12 years, most recently with a modified XSi and T2i. This summer, I bought the ASI1600MC-C and have been using it regularly for a couple of months. Based on my experience, the set-point cooling of the 1600 is the only significant difference impacting image quality, but it is enough of a difference to result in an improvement in my images. Specifically, I have found it unnecessary to use any type of noise reduction on images because of the cooled subs taken with the 1600. There is less loss of detail that would result from using NR compared to DSLR images. Even when imaging on a cool or cold night this summer, there was an improvement in faint detail in images compared to those taken with my non-cooled DSLRs, because the non-cooled DSLRs generate heat that result in noise in an image even on a cold night. Bottom line is that processing is just easier with the cleaner 1600 data.

Mike


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#33 RRod

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Posted 22 September 2016 - 03:15 PM

Hi Mike

 

I have exactly the same cameras (Xsi and T2i). I agree that although the cameras are good you have to use a lot of noise reduction as well as integration time, specially the Canon T2i which heats up much more than Xsi. Even with 10h of integration time, noise reduction has been necessary thus lost of fine details. My next steps is going to the ASI1600 which I am consider to buy soon

 

Rodrigo



#34 Poochpa

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Posted 22 September 2016 - 04:00 PM

Hi Mike

 

I have exactly the same cameras (Xsi and T2i). I agree that although the cameras are good you have to use a lot of noise reduction as well as integration time, specially the Canon T2i which heats up much more than Xsi. Even with 10h of integration time, noise reduction has been necessary thus lost of fine details. My next steps is going to the ASI1600 which I am consider to buy soon

 

Rodrigo

Hi Rodrigo,

You will be happy with the ASI1600. I fully agree with you about the T2i v. the XSi. Here are images of the Crescent Nebula taken with the 1600 and the XSi, respectively. Same scope, but different locations and integration time. The 1600 image was taken at a semi-rural location, combining Ha (12x600s) and color (31x300s).  The XSi image was taken at a true dark sky location, 36x360s, ISO 800.

Mike

 

ASI600 Image:

Attached Thumbnails

  • CrescentRGB+HA2 copy800.jpg

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#35 Poochpa

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Posted 22 September 2016 - 04:01 PM

XSi Image:

 

Attached Thumbnails

  • CrescentCN.jpg


#36 RRod

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Posted 22 September 2016 - 05:24 PM

Hi Mike

That is really amazing!! It also shows you are using your clear and moonless night  much more efficient. So far, I am waiting for Sam to come with the narrow band filters. I would like to buy the kit. He asked me what I would prefer: the 31 or 36 mm. I gues both would work with my scopes so price will make the difference.

Rodrigo



#37 Jon Rista

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Posted 22 September 2016 - 10:56 PM

How about some real data from an actual AS1600MM-Cool? Here is what I am doing at Gain 200, 90 second subs, and 3nm narrow band filters in a red zone...yes, I did say NINETY SECOND narrow band subs:

 

Bubble Nebula

 

Total Integration: 1h45m

 

Ha: 9x90s (13.5 minutes)

OIII: 25x90s (37.5 minutes)

SII: 36x90s (54 minutes)

 

RFV3uzz.jpg

 

Pelican Nebula

 

Ha: 35x90s (52.5 minutes)

 

DIMep80.jpg


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#38 Jon Rista

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Posted 22 September 2016 - 10:57 PM

Great Wall

 

Ha: 25x90s (37.5m)

 

ZfNfqml.jpg

 

Wizard Nebula

 

Ha (as Luminance): 82x90s (2h)

 

Ha: 16x90s (24 minutes)
OIII: 27x90s (40.5 minutes)
SII: 35x90s (52.5 minutes)

 

SJx1Qtj.jpg


Edited by Jon Rista, 22 September 2016 - 10:58 PM.

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#39 Jon Rista

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Posted 22 September 2016 - 10:57 PM

Soul Nebula (2x1 Mosaic)

 

Total Exposure: 5h15m

 

Ha: 105x90s (2h37m30s (per panel))

 

VDknWsK.jpg

 

PLMHmZi.jpg


Edited by Jon Rista, 22 September 2016 - 11:06 PM.


#40 Jon Rista

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Posted 22 September 2016 - 11:05 PM

Maybe this will settle any questions about whether a 12-bit camera is good enough or not. ;) With sufficient stacking...which, when your looking at 30, 60, 90 second subs for both narrow band and LRGB, is really not an issue...you average out the noise, including quantization noise, and recover bit depth and dynamic range. So, 12-bit? Not a problem. 

 

Beyond that...90 second narrow band subs. I don't know if anyone's eve done that with results like the above before the ASI1600 came along. Even on a very, very faint target like CTB-1, on a night of horrible transparency, with a fairly bright half moon in the sky (which just made the bad transparency all that much worse)...I was able to get his in four hours with 120 second subs (you usually see tens of hours on this object, with 1800-3600 second exposures):

 

ZkpEGTD.jpg

 

The ASI1600MM-Cool is an awesome little camera. As a DSLR user myself, and a DSLR user who has been able to create some great images with my 5D III, I can say with utmost confidence that the ASI1600 was worth every penny. Reports that it is overpriced or insufficient because of bit depth or that the glows are a big problem or anything like that are totally overblown. For a DSLR imager stuck in a city, it's no contest. This little red camera will wipe the floor with any DSLR here, to China and back again. Perhaps the only thing that might compare on the DSLR front is a mono-modded, cold-fingered DSLR mod using narrow band filters...the DSLR would have an FoV advantage. Outside of that...I see no contest between DSLRs, even astro modded, and the ASI1600. 

 

All you need to know is in the images just above. 


Edited by Jon Rista, 23 September 2016 - 03:18 PM.

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#41 JukkaP

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Posted 23 September 2016 - 12:18 AM

Great pictures Jon! There can be no comparison over mono and color sensor. For sure mono is allways better for dso.

The overall cost is so great that it does not fit for everyone. Another point is that changing to dedicated astrocamera is a big step. So its only natural to chalenge this new class what is direct dslr rival.

I'am in that point i need to change from the beginner class to intermediate. So: new mount, new scope, new camera. Its 5-8k.. Trying to wait for the next gen of these big sensor astrocameras.
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#42 RRod

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Posted 23 September 2016 - 02:30 PM

Hi

the pictures are really nice. I actually have a mono mod Xsi and although I got nice pics, no way I can do 90s exposures with my 7nm Ha filter. My exposures have to be 10min or more to get something good and at least 7h of integration time to reduce noise. For sure I am buying the camera soon :)

thank you for posting the pics 

Rodrigo


Edited by RRod, 23 September 2016 - 02:31 PM.


#43 Jon Rista

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Posted 23 September 2016 - 03:38 PM



The 6D is 14 bit (as are some other DSLRs), 20 meg with 6.55 micron pixels, 43.04 mm on diagonal sensor. There is also more in camera (DIGIC) processing for noise reduction, color balance etc.   So not really comparable to the ASI1600.  It might be more comparable to the older smaller sensor EOS cameras.  

In my honest opinion, having used a 5D III (which is fairly close to the 6D in terms of performance...the 6D has slightly less dark current noise, both still have banding) quite extensively under good, dark skies...I still think it would be no context between the ASI1600 and the 6D. Because of the extremely low noise and high sensitivity of the ASI1600, the tiny pixels, and the option to either use an L filter with LRGB, or narrow band filters (or both!), you could mosaic a field large enough to fill the 6D frame, and have at least a similar SNR (however, on a normalized basis, SNR would likely be much better), in about the same amount of time it would take you to get a decent SNR with the 6D.

 

I've been working on a mosaic of the Cygnus North America and Pelican nebula region for a few nights now. I am getting no more than about 37.5 minutes per PANEL, and you can stack four panels to get about a 33.5x25mm FoV. So in 2h30m, you could have a full frame FoV with quality like this:

 

a2z5vto.jpg

 

Here is a 100% crop for examination of the noise details...and, check out the TINY stars...with a low pass filter and the need to demosaic, a DSLR could never produce stars that small...even with smaller pixels. The filter and the demosaicing blur too much:

 

IySjpCu.jpg

 

Also compare the quality of the noise. Even at ISO 1600, which tends to deliver the best noise quality on the 5D III...it is not even remotely close to the kind of clean, low, random noise characteristic you can get with the ASI1600. Even in the poor signal areas of the dark dust...the noise still maintains an exceptional gaussian quality. I'd love to see a 6D produce detail and quality like this at full size in just two and a half hours. An ASI1600 mosaic would also be 64 megapixels, rather than 20...downsample the ASI1600 mosaic to the same pixel dimensions as the 6D image, and you reduce noise and improve SNR even more. 

 

There is no contest here. These are 90 second 3nm narrow band Ha subs, only 37.5 minutes of integration. Possibly outside of a cold fingered mono-modded full frame DSLR (and even then, I'm skeptical, due to the loss of microlenses in the mono-modding process), DSLRs don't stand a chance here. 


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#44 Ron359

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Posted 23 September 2016 - 07:09 PM

 



The 6D is 14 bit (as are some other DSLRs), 20 meg with 6.55 micron pixels, 43.04 mm on diagonal sensor. There is also more in camera (DIGIC) processing for noise reduction, color balance etc.   So not really comparable to the ASI1600.  It might be more comparable to the older smaller sensor EOS cameras.  

In my honest opinion, having used a 5D III (which is fairly close to the 6D in terms of performance...the 6D has slightly less dark current noise, both still have banding) quite extensively under good, dark skies...I still think it would be no context between the ASI1600 and the 6D. Because of the extremely low noise and high sensitivity of the ASI1600, the tiny pixels, and the option to either use an L filter with LRGB, or narrow band filters (or both!), you could mosaic a field large enough to fill the 6D frame, and have at least a similar SNR (however, on a normalized basis, SNR would likely be much better), in about the same amount of time it would take you to get a decent SNR with the 6D.

 

I've been working on a mosaic of the Cygnus North America and Pelican nebula region for a few nights now. I am getting no more than about 37.5 minutes per PANEL, and you can stack four panels to get about a 33.5x25mm FoV. So in 2h30m, you could have a full frame FoV with quality like this:

 

 

 

Here is a 100% crop for examination of the noise details...and, check out the TINY stars...with a low pass filter and the need to demosaic, a DSLR could never produce stars that small...even with smaller pixels. The filter and the demosaicing blur too much:

 

 

 

Also compare the quality of the noise. Even at ISO 1600, which tends to deliver the best noise quality on the 5D III...it is not even remotely close to the kind of clean, low, random noise characteristic you can get with the ASI1600. Even in the poor signal areas of the dark dust...the noise still maintains an exceptional gaussian quality. I'd love to see a 6D produce detail and quality like this at full size in just two and a half hours. An ASI1600 mosaic would also be 64 megapixels, rather than 20...downsample the ASI1600 mosaic to the same pixel dimensions as the 6D image, and you reduce noise and improve SNR even more. 

 

There is no contest here. These are 90 second 3nm narrow band Ha subs, only 37.5 minutes of integration. Possibly outside of a cold fingered mono-modded full frame DSLR (and even then, I'm skeptical, due to the loss of microlenses in the mono-modding process), DSLRs don't stand a chance here. 

 

Yeah, I get it; you are falling over in love with your ASI1600.  When I posted my comment after the OP, I thought he/she was asking about a direct comparison of the bayer color ASI1600 v. a DSLR 6D, which seems a reasonable question. So I posted the spec of the 6D sensor, which has a much larger sensor.   Why anyone would directly compare a DSLR uncooled bayer sensor to a mono cooled filtered camera does not seem a reasonable comparison.  Obviously a mono sensor with NB filters has 3 x the bit depth when producing color pics, plus the low noise cooling etc.

 

 If you really want to compare, compare the total package;  the cost of a similar/same size sensor mono cooled CCD + filters, filter wheel etc, to the 6D.  Then you might be in sticker shock like me.  Which is why many of us stick to DSLR imaging even when its obvious cooled mono cameras are technically better.  No one doubts that unless they don't know the differences.  If you didn't already realize it, one amazing point of DSLR imaging is that you can come awfully close to those cooled ccd images for an order of magnitude less money.  For some of us, part of the fun is astro imaging with something that doesn't cost a year of our kids in college, cause we have to choose. And its really not a choice which is more important.  It is nice to see a lower priced CMOS camera come on the market that starts to be of interest to DSLR users.  

 

Both these methods only get better with time.  Hopefully all the gains won't be wiped out (literally) by broad spectrum LED light pollution. 


Edited by Ron359, 23 September 2016 - 07:11 PM.


#45 Jon Rista

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Posted 23 September 2016 - 07:39 PM

The title clearly called out the ASI1600MM-Cool for comparison.

 

The cost of a full package for the ASI1600 is not that insane, and as I said, it could mosaic narrow band data at least as fast if not faster than you could acquire enough SNR for a single full frame with the 6D (at a dark site, at that! Not a chance in hell in a light polluted zone.) ZWO is selling a packaged kit with camera, filter wheel and filters formulated specifically for this camera for $1500. Or you could pick up the filter wheel and a narrow band filter for the same price. Or you could skip the filter wheel and just use a single Ha narrow band filter for less. A brand new 6D costs $1200. An astro mod to improve it's red performance costs several hundred dollars. To use the OSC optimially, you either need very dark skies, or an LP filter, which is another $150-$190. So, what sticker shock? We don't need to compare to the KAI-11002 anymore. It's beyond impractical...especially considering a KAI-11002 starts out with 15e- read noise and has considerable dark currrent even when cooled. The 6D at high ISO actually surpassed the 11002 when it was released. 

 

It's a different game now. The ASI1600 is just the first of many such cameras, and it isn't the only option if you are willing to pair a smaller sensor with a shorter lens...some of the smaller sensors are even better specs wise than the ASI1600. With prices in the same ballpark as full frame DSLRs, it's going to be harder and harder to justify all the money you would have to spend on a FF DSLR and necessary accessories (like LP filters and astro modding) when you could get better, richer results with a CMOS astro camera, often in less time. Oh, and as far as FoV goes? You can always use a shorter focal length...these modern CMOS cameras have tiny pixels, no low pass filter, and require no demosaicing. You could easily use half the focal length, double your FoV, and still get better resolution than a 6D could deliver.



#46 whwang

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Posted 23 September 2016 - 08:01 PM

I don't want to get into most of the debates.  Just let me point out one thing.  When we talk about Bayer sensors vs mono sensors, let's not forget that there is a processing technique called Bayer drizzle.  It allows you to obtain image resolution equivalent to what can be achieved with mono sensors of the same pixel size. This function has been offered by DSS since day one.  I see little reason to ignore it and then complain about the resolution from Bayer sensors.


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#47 Jon Rista

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Posted 23 September 2016 - 09:10 PM

I don't want to get into most of the debates.  Just let me point out one thing.  When we talk about Bayer sensors vs mono sensors, let's not forget that there is a processing technique called Bayer drizzle.  It allows you to obtain image resolution equivalent to what can be achieved with mono sensors of the same pixel size. This function has been offered by DSS since day one.  I see little reason to ignore it and then complain about the resolution from Bayer sensors.

Drizzling can help, however it is highly unlikely to overcome all the blurring caused by a low pass filter and demosaicing. I went from an average of 5-6" FWHMs with my 5D III, to 2-2.3" FWHMs with my ASI1600, on the same lens. I've drizzled a majority of my 5D III data, and I've come nowhere close to that kind of a resolution improvement. I do see improvements, particularly when using 2x scale with a drop shrink of 0.7 in PixInsight (which is quite superior to DSS's drizzling capabilities), however I usually still don't even get below 4". 

 

And the resolution improvement is only one of the benefits. The bigger benefit is really the full fill factor, higher sensitivity, and ultra low noise. For imagers stuck with light pollution, the efficiency improvements in gathering photons, and gathering as many photons as possible is the best way to overcome LP, are very worthwhile. Throw in the narrow band options...I see very little reason anyone who cannot visit a dark site on a regular basis to keep using a DSLR (or for that matter any OSC camera.)

 

Anyway. I'll leave it at that. I think the images will speak for themselves for the most part. ;) People can choose what's best for them. 



#48 entilza

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Posted 23 September 2016 - 09:16 PM

Wei-Hao, I have been using a Nikon for a while now, and still enjoying it, I am on the fence about getting one of the new cooled cameras, but I am wondering if I should just get my D5300 full spectrum modified.  Do you think it would be of much benefit?



#49 mmalik

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Posted 23 September 2016 - 10:47 PM

People use DSLRs mainly for their form factor and utilitarian nature (take daytime pics of kids, take night time pics of stars). The roundy or boxy form factors will always be a hindrance to their adoption or longevity. Plus blinding pace of research and development alone sets DSLRs apart; add cooling... to a low noise DSLR and you've got it made. Regards

 

 

post-205769-0-18375500-1469683633.jpg



#50 Jon Rista

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Posted 23 September 2016 - 11:02 PM

People use DSLRs mainly for their form factor and utilitarian nature (take daytime pics of kids, take night time pics of stars). The roundy or boxy form factors will always be a hindrance to their adoption or longevity. Plus blinding pace of research and development alone sets DSLRs apart; add cooling... to a low noise DSLR and you've got it made. Regards

 

 

post-205769-0-18375500-1469683633.jpg

I disagree on all points. The pace at which ZWO has been cranking out new cameras has outpaced that of DSLR/mirrorless manufacturers. QHY is also progressing at a high pace, faster than DSLRs & mirrorless, but slower than ZWO. With the pace at which sensor innovation is occurring (which also outpaces DSLR/Mirrorless releases), I expect to see continued rapid innovation in the astro camera space. A couple of people in the sensor industry have mentioned in a couple of threads now that sensors with much less than 1e- read noise are on the way, and I expect to see such a sensor in a camera from ZWO long before such a sensor ends up in a DSLR. 

 

Adding cooling like you are talking about to a DSLR or mirrorless doesn't come close to giving you the kind of performance you can get at -15C on one of these astro cameras, which is around 0.008e-/s dark current. Bolt-in coolers are also only really viable in a stable environment...the moment you enable live view or any other heat-inducing feature, the cooler can't keep up. With dual-stage regulated cooling, I have been able to maintain exactly -20.0C temps throughout the entire night with the ASI1600 once equilibrium was reached. Not even a +/- 0.1C discrepancy, despite as much as a 15C drop in ambients over the course of the night.

 

As for form factor, well, to each his own. I can't speak for anyone but myself there...I still have my DSLRs. However they are so far behind on the IQ front that I haven't used any for astro since the middle of Winter. 


Edited by Jon Rista, 23 September 2016 - 11:03 PM.

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