ZWO ASI2600MM-Pro vs Cooled and Modded DSLR image quality

[MarsG76]

Hello All,

Can I pick your brains for info?

After a long resistance, I finally bit the bullet and ordered a dedicated astro camera... the ZWO 2600MM-P.... which will be in my hands in around a month... But I have some reservations to whether I just spent a heap of cash for minimal or no improvement in my images.

Basically I have been using a full spectrum modded and peltier cooled Canon 40D, cooled using two peltiers on opposite sides of a cold finger, and the cooling works very well.... I have a temperature controller on the system with a thin temperature probe sitting between the cold finger and the sensor, this way reporting an accurate sensor temperature. I limit the cooling to 4 degrees C (it has reached -4.7C during a test, but the sensor hazed over)... I find that down to 4 degrees (with a heat strip wrapped around the front of the DSLR/Filter wheel connection) I do not have any condensation issues on most nights and at 8 degrees or lower, my ISO1600 subs are noise free, even if I'm exposing up to 1800 second subs.

Now to my dilemma, when I try to look up if anyone has compared a DSLR setup similar to mine to a dedicated astro cam such as the ZWO2600MM out on the field (as opposed to tech spec sheets), there aren't many comparisons and the two posts that I found that are the closest to comparisons show that there is not that much difference in the overall images... one camera was a cooled 40D compared to a QHY OSC camera and the images of the Rosette nebula (featured/tested/compared) were very similar and a image of M31 actually looked better taken with a modded Canon 5Dmk3 to the one imaged with a ZWO1600MM by the same imager, using the same scope!!!

Would anyone be able to answer whether I should be bracing for a disappointment?

 

Once I get it, I'll do a direct head to head comparison on the same object, same focal length, and compare both RGB and Narrowband imaging. (And I was having success in Hubble Palette style narrowband imaging with my DSLR so the statements, that are quite frequent or forums, that NB imaging with a DSLR is a waste of time are simply not true IMHO).

 

Thanks in advance.

MG

 

 

[almcl]

Can't give an identical comparison, but I recently acquired a ASI 2600 MC to replace my cooled Canon 700d.  I wasn't brave enough to insert cold fingers into the camera, so its cooling merely reduced the EXIF reported temperature by about 10 or 12 º  C.  

The few results the weather has allowed with the 2600 suggest that it's quite a marked improvement over the DSLR.  Cooling set to -10ºC , no misting.  No amp glow (my Canon suffered really badly from this), very low noise, lighter weight on the focuser.  

There were software problems initially; APT wouldn't download the image files, but a new driver from ZWO and updates from Ivo fixed that, I need a replacement focuser for the MN190, because although the 2600 is lighter than my Canon+cooler, the weight is further out and causes tilt.  The weather has also been awful and getting 20 lights on a target has been all but impossible so I can't post any comparable before and after shots, but a couple of early attempts are here:

 

 

My previous DSLR images with these targets were with a different scope, but were nothing like as good.  But then the processing software has changed, too.

 

Edited February 22, 2021 by almcl

[MarsG76]

On 23/02/2021 at 09:56, almcl said:

Can't give an identical comparison, but I recently acquired a ASI 2600 MC to replace my cooled Canon 700d.  I wasn't brave enough to insert cold fingers into the camera, so its cooling merely reduced the EXIF reported temperature by about 10 or 12 º  C.  

The few results the weather has allowed with the 2600 suggest that it's quite a marked improvement over the DSLR.  Cooling set to -10ºC , no misting.  No amp glow (my Canon suffered really badly from this), very low noise, lighter weight on the focuser.  

There were software problems initially; APT wouldn't download the image files, but a new driver from ZWO and updates from Ivo fixed that, I need a replacement focuser for the MN190, because although the 2600 is lighter than my Canon+cooler, the weight is further out and causes tilt.  The weather has also been awful and getting 20 lights on a target has been all but impossible so I can't post any comparable before and after shots, but a couple of early attempts are here:

 

 

My previous DSLR images with these targets were with a different scope, but were nothing like as good.  But then the processing software has changed, too.

 

The cooled camera seems to give you very clean images, but, even though a DSLR is rougher, overall, I think that a cooled DSLR is not that much worse... I'm now hoping that with the cleaner subs, I'll be able to capture the same about of photons in much less time due to being the camera being mono and has a QE of 91%... surely no bayer filters and 3X the QE should result in considerably faster captures.

[SteveNickolls]

Hi Mars G76, thanks for starting this thread. It will be fascinating to see your future comparisons of images between the two set up’s. The difference between theory and practice-lovely.

I have been viewing the ASI2600MM as a potential future replacement for my modified Canon 700D for wide field nebula work. 

On 26/02/2021 at 02:25, MarsG76 said:

the camera being mono and has a QE of 91%...

The peak 91% QE isn't perhaps where you would wish it on the monochrome sensor, the graph below is from the FLO site for the ASI2600MM-Pro USB 3.0

At the Ha wavelength the QE drops to the mid-upper 50's, ok the OIII and Hb are much higher but the SII is even lower than for Ha.

You will also benefit from the lack of a Bayer array with the mono-sensor allowing more useful light to be captured by the sensor than your existing camera.

Good luck with the new acquisition. Look forward to your comparisons.

Cheers,
Steve

 

 

[MarsG76]

On 05/03/2021 at 19:19, SteveNickolls said:

The difference between theory and practice-lovely.

Hi Steve... I'll definitely be doing a full comparison...

Currently I'm imaging NGC3603... the "Statue of Liberty" nebula in between cloudy & near full moon lit nights. I'm getting more than my fair share of cloud covered nights lately, but it's early in the season and if I get another two or three clear nights in the next 2 weeks than I'll complete this Cooled full spectrum DSLR version just as the 2600MM is due to arrive... than I'll still have enough time do the same image, using the same scope and filters with the new astro cam... this would be my first head to head comparison. 

[MarsG76]

On 05/03/2021 at 19:19, SteveNickolls said:

At the Ha wavelength the QE drops to the mid-upper 50's, ok the OIII and Hb are much higher but the SII is even lower than for Ha.

You will also benefit from the lack of a Bayer array with the mono-sensor allowing more useful light to be captured by the sensor than your existing camera.

Good luck with the new acquisition. Look forward to your comparisons.

The QE is still higher on this graph than, in theory, on a full spectrum modded DSLR.... (by a factor or 3?) added with the lack of the bayer matrix, this theoretically should cut exposure times by 12X for equivalent subs brightness/photon collection.... but theory and practice hardly ever match up.  

[SteveNickolls]

Thanks for doing this comparison MarsG76 I am really interested in the practical improvements when compared to the theoretical advantages of the monochrome camera. I've never been quite sure of the QE of the Canon 700D at Ha wavelength either before or after modding except it improves the results dramatically compared to my unmodded Canon 600D which is all but useless for imaging DSO's under the light polluted conditions here. I still think the quantum efficiency at Ha wavelength for the ASI2600MM is low (compare the ASI294MM at around 76% at that wavelength and the older ASI183MM is around 78%), but in this hobby we get sensors reused for our purposes. The read noise of the ASI2600MM will also be a big improvement over that from a DSLR allowing shorter sub exposures.

May I ask what type of night sky you are able to image under?

Good luck.

Cheers,
Steve

 

[MarsG76]

8 hours ago, SteveNickolls said:

Thanks for doing this comparison MarsG76 I am really interested in the practical improvements when compared to the theoretical advantages of the monochrome camera. I've never been quite sure of the QE of the Canon 700D at Ha wavelength either before or after modding except it improves the results dramatically compared to my unmodded Canon 600D which is all but useless for imaging DSO's under the light polluted conditions here. I still think the quantum efficiency at Ha wavelength for the ASI2600MM is low (compare the ASI294MM at around 76% at that wavelength and the older ASI183MM is around 78%), but in this hobby we get sensors reused for our purposes. The read noise of the ASI2600MM will also be a big improvement over that from a DSLR allowing shorter sub exposures.

May I ask what type of night sky you are able to image under?

Good luck.

Cheers,
Steve

 

Ultimately I'm hoping for a major improvement... There are reports (or opinions) that the 2600MM will "change the game" or "change everything" as stated by a fellow (Astro Backyard)  who reviews astro gear...  

Modding the DSLR is night and day to what it did to sensitivity, especially in HAlpha... and looking at the graph attached, taking the (deeper) cooling, read noise and no bayer filters, gives me hope....

Comparing these graphs... I should capture HAlpha signal 9.6X faster and SII 14X faster with the 2600MM compared to my 40D??

I imagine that DSLR QE would be similar across the board.... so your 700D should be similar.

 

My skies are around Bortle 4-5....

 

 

Edited March 7, 2021 by MarsG76

[MarsG76]

Add to that.... I want to say, I wish that the camera would get here already so I can test, but as we all know... it's been mostly cloudy since I ordered it and when it arrives, it'll be solid cloud for another 2-3 months... and unlike now.. with no break in the weather what so ever... 

Edited March 7, 2021 by MarsG76

[MarsG76]

Super imposing the QE graphs from few different types of camera states that the 2600MM should be a performer.... In theory exposure times should be 12 time shorter with the 2600MM than with my 40D for equivalent amount of photons captured... 3X the QE and another 4X the speed due to no bayer matrix...

Am I missing something?

[rsarwar]

if you wish to take a luminus shot, sure 12x at 450 nm in terms of exposure time. or about 8x at Ha in terms of exposure time. but when you add a filter, red/blue/green, you would only see about 2x on Ha in terms of exposure time assuming you are using modded cam. that is the theoretical max.

going back to 40d, that sensor has larger pixels sizes compared to asi2600/qhy268. so some of what you gained through QE will be lost there.

so i personally would not expect the exposure time to be smaller than 1.6-1.8x shorter when using a red filter/Ha filter

In terms of resolution however, you will see a mark improvement, at least 5 times

Edited March 14, 2021 by rsarwar

[michael.h.f.wilkinson]

I do DSO imaging with a mixture of cameras. My first DSO camera I used seriously is the modded Canon EOS 550D which I still use for wider targets. I then added an ASI183MC (non-cooled), initially for planetary and lunar, but later for DSOs as well, and find it a lot more sensitive. Most recently, I added an ASI183MM-Pro, and it is another step further in terms of image quality. I do not doubt your ASI2600MM will clearly outperform the modded, cooled 40D

[sharkmelley]

The Canon 40D uses an old sensor with very low QE (quantum efficiency).  A more recent camera will have vastly improved QE.  You can choose either a modern consumer camera and have it modified or a dedicated OSC astro-camera because in many cases they use exactly the same sensor.  Both will be a huge improvement over the modified 40D.  Obviously the dedicated astro-camera will have much lower thermal noise because of cooling.

Mark

Edited March 22, 2021 by sharkmelley

[MarsG76]

10 hours ago, sharkmelley said:

The Canon 40D uses an old sensor with very low QE (quantum efficiency).  A more recent camera will have vastly improved QE.  You can choose either a modern consumer camera and have it modified or a dedicated OSC astro-camera because in many cases they use exactly the same sensor.  Both will be a huge improvement over the modified 40D.  Obviously the dedicated astro-camera will have much lower thermal noise because of cooling.

Mark

Do you know this for a fact??? I seen similar statements online in various forums but no head-head comparisons.

My 40D is cooled so thermal noise is of no issue...

Eitherway, my 2600MM should be here within days so I'll compare the two and see the difference between the two when used in real world practice... graphs and company generated numbers hardly ever reflect real life use.

Edited March 22, 2021 by MarsG76

[rnobleeddy]

12 minutes ago, MarsG76 said:

Do you know this for a fact??? I seen similar statements online in various forums but no head-head comparisons.

My 40D is cooled so thermal noise is of no issue...

Eitherway, my 2600MM should be here within days so I'll compare the two and see the difference between the two when used in real world practice... graphs and company generated numbers hardly ever reflect real life use.

I don't know how accurate it is, but see https://www.dpreview.com/forums/thread/2750802 - if that's believed, the older DSLR sensors are quite a bit worse.

 

Anecdotally, I also owned a colour Atik 383 which is famed for having one of the worse QE of any astro camera, somewhere in the 40s. I didn't find that a massive improvement over my DSLR.

[MarsG76]

15 minutes ago, rnobleeddy said:

I don't know how accurate it is, but see https://www.dpreview.com/forums/thread/2750802 - if that's believed, the older DSLR sensors are quite a bit worse.

 

Anecdotally, I also owned a colour Atik 383 which is famed for having one of the worse QE of any astro camera, somewhere in the 40s. I didn't find that a massive improvement over my DSLR.

I don't find my modded and Cooled 40D that bad at all... in actual fact I'm very happy with my results that I get with it.... I'm more hoping that the increased QE and no bayer matrix will cut my exposure time down by 5-10 times over expecting an increase in detail/resolution since the atmosphere is probably a big limiter of detail at 2000mm focal length.

 

[sharkmelley]

4 hours ago, MarsG76 said:

Do you know this for a fact???

Which part of what I said?

Mark

[MarsG76]

7 hours ago, sharkmelley said:

Which part of what I said?

Mark

That recent sensors are more sensitive, higher QE, than the one in the 40D, even though the 40D sensor has physically bigger pixels and hence a greater surface area to capture photons.

 

[sharkmelley]

The 40D is approx 14 years old!  There have been huge advances since then.  Look at this chart comparing the 40D to a more recent camera:

https://www.photonstophotos.net/Charts/Sensor_Characteristics.htm#Canon EOS 40D_14,Canon EOS 7D Mark II_14

The 7DII has nearly twice the QE of the 40D.  That means the sensor as a whole will capture twice as many photons from the same scene in the same exposure time.

Mark

Edited March 23, 2021 by sharkmelley

[rsarwar]

I doubt you will see anywhere near what you are expecting. The math is very simple really if you are to only consider filters, pixel size and qe

Say you have 100 ha emission photons coming in per second per 1 micro meter squaeree (area in 1 um²) With 60 pc efficiency on Ha, you would capture 60 of them per second per um². Similarly for 40d, you would get 25 of them per second per um². 

 

Now consider pixel size. With 3.7 um pixel size, asi2600 would capture 60*3.7*3.7 or 821 photons per second per pixel. Similarly for 40d, that value is 812 (5.7 um).

For peak transmission,  asi2600 is 1095 vs 40d is 1137 photon per second per pixel

 

Pixel size matters. that is why we use large pixel sizes with long focal lenght (after considering undersampling/oversampling reasons)

 

This however does not take into account improvements in the readout electronics. Also since your new sensor has smaller pixel, it will have less noise, so you would need to stack less frames

 

The impact of color bayrr matrix is minimal on efficiency, as the debayering algorithm interpolate and fill in missing photons due to the filters.

 

Ps, I am expecting my qhy268 in the next couple of weeks and be happy to test against d7000, unless you get yours first and post results

Edited March 30, 2021 by rsarwar

[MarsG76]

I see your point but this can not be right... if it was it would all but make it pointless to spend the premium money on Astro cams, and sticking to modded DSLRs with big pixels would deliver same or similar results...

I'll definitely be makng a comparison between the two and if the 2600MM is no better or marginally better than the 40D... I'll be severely [word removed] off.

Time will tell...

[rsarwar]

One also has to consider that large pixel size would result in softer images. So you can't simply start using a camera with the largest pixel size

It will still be better than 1600 which is what most people will compare with as they have similar pixel size.

Also you have to consider that you would have to stack less frames. What I suggested us that having a 2600 camera will not create a significantly brighter image for a given exposure time.

Having said that - i am secretly hoping that i am wrong and that you are correct.

 

the main reasons i have considered a didcated astro camera is to go mono, cooling and shutter shake.

Edited March 31, 2021 by rsarwar

[sharkmelley]

14 hours ago, MarsG76 said:

I see your point but this can not be right... if it was it would all but make it pointless to spend the premium money on Astro cams, and sticking to modded DSLRs with big pixels would deliver same or similar results...

The main difference is the noise reduction from the cooling.  Otherwise a modded DSLR/mirrorless can produce very similar results because in many cases dedicated one-shot-colour astrocams use the same sensor as a modded DSLR/mirrorless camera.

Mark

[Merlin66]

They may have the same sensor, but the built-in additional UV-IR and colour correction filters in the DSLR etc. dramatically change the outcome.

 

[sharkmelley]

1 hour ago, Merlin66 said:

They may have the same sensor, but the built-in additional UV-IR and colour correction filters in the DSLR etc. dramatically change the outcome.

I purposely said modded DSLR/mirrorless i.e. the bare sensor without the filter stack which is removed during modification.