Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Understanding the ZWO ASI 294MM Pro Camera

  • Please log in to reply
7 replies to this topic

#1 StevenBellavia

StevenBellavia

    Viking 1

  • *****
  • topic starter
  • Posts: 830
  • Joined: 11 Mar 2014
  • Loc: New York

Posted 01 June 2021 - 05:06 AM

Like other new CMOS cameras being introduced into the astrophotography market, the ZWO ASI 294MM Pro seems to be a strange beast (but not in a bad way).The first thing to notice is that it has a “jump” in performance at Gain 120.

Click here to view the article
  • Ken Sturrock and druhela like this

#2 rcol

rcol

    Vostok 1

  • *****
  • Posts: 116
  • Joined: 11 Mar 2020

Posted 03 June 2021 - 11:17 AM

How much of this might apply to the OSC version, i.e., ASI294MC PRO ?


  • Bob Campbell likes this

#3 const

const

    Vostok 1

  • -----
  • Posts: 188
  • Joined: 11 May 2020
  • Loc: WA

Posted 04 June 2021 - 12:57 PM

How much of this might apply to the OSC version, i.e., ASI294MC PRO ?

There is no corresponding bin1 mode in ASI294MC. The sensors are different, IMX294 in ASI294MC and IMX492 in ASI294MM. Not sure how much they are different besides CFA. The IMX294 is 'Quad Bayer' with similar 2.3um pixels grouped by 4 into larger pixels, then covered with CFA. Even if the sensor itself has similar bin1 mode, software would have hard time interpreting that funny Bayer pattern.


  • StevenBellavia likes this

#4 lowry_pt

lowry_pt

    Explorer 1

  • *****
  • Posts: 89
  • Joined: 07 Aug 2018
  • Loc: South of Indianapolis, IN

Posted 23 June 2021 - 11:29 PM

Excellent article and I was following along, surprisingly quite well, until the end where I got lost. So can you kind of explain again in the binning for dummies version.

 

bin 1x1 at gain 120 is......

bin 2x2 at gain 120...  etc...  

 

THANK YOU

 

Dawn


  • StevenBellavia and jmfdiver like this

#5 AZAstro01

AZAstro01

    Lift Off

  • *****
  • Posts: 2
  • Joined: 25 May 2021

Posted 27 June 2021 - 04:08 PM

Great info I would that same type of article for the 2600MC pro
  • StevenBellavia likes this

#6 StevenBellavia

StevenBellavia

    Viking 1

  • *****
  • topic starter
  • Posts: 830
  • Joined: 11 Mar 2014
  • Loc: New York

Posted 28 June 2021 - 08:26 PM

Excellent article and I was following along, surprisingly quite well, until the end where I got lost. So can you kind of explain again in the binning for dummies version.

 

bin 1x1 at gain 120 is......

bin 2x2 at gain 120...  etc...  

 

THANK YOU

 

Dawn

Hi Dawn,

 

I am not sure I understand the question, because I am a dummy. 

But I will try to answer what I think you are asking:

 

In BIN 1 mode, there is nothing special about Gain 120, versus Gain 100, Or Gain 140, or even Gain 119 or Gain 121.  In BIN 1 mode, Gain 120 is close to unity gain

(A sensor analysis I performed in SharpCap shows it to be around 111 for my camera, which is oddly similar to the ZWO ASI 183, and that is pretty much how the 294MM performs in BIN 1 mode).  Gain 120 is just one of the many choices available*.

 

*The Gain you choose, also depends on many things, and I have developed spreadsheets that try to help narrow down the choice of gain and sub-exposure as a function of your sky's brightness, telescope and filter used:

 

https://www.cloudyni...or-zwo-cameras/

 

But in BIN 2 mode, Gain 120 is very special.  Yes, like BIN 1, it too is close to unity gain.  But a large increase in performance occurs at or above Gain 120 (and I don't know how they do it, as I am more of a math person than an electronics guru). Below Gain 120 there is 3X as much read noise, and you lose dynamic range, since that is a function of the full well count (which has a more gradual, steady change) and the read noise (which goes up dramatically below Gain 120).  And in fact, if you look at the BIN2 performance curve (attached /below), you don't catch up to the Gain 120 dynamic range until you get to Gain 0.

 

I don't like giving advice (as I am in no position to), but I don't see much benefit using Gains lower than 120 in BIN 2 mode. (but many people do, and I am sure with good reasons.  One reason might be just to be able to use longer sub-exposures.  And that is a good reason if you don't feel like filling up your hard drive. And many short sub-exposures are less efficient, due to download time between each exposure as well as dithering, etc., so that is another good reason).

 

So I hope that answers your question regarding  BIN 1 versus BIN 2 at Gain 120. 

 

I also hope I explained correctly in my article that going from BIN 1 to BIN 2 is simply achieved by changing the BIN setting in whatever image capture software you use, as it should have that option.

 

And lastly, whether you choose BIN 1 or BIN 2 opens up an entirely new discussion regarding sampling and resolution.  This then involves telescope aperture, f/#, atmospheric seeing conditions, guiding performance, final integrated SNR, as well as your personal preference in how your image "looks".  There are numerous threads on this topic. 

The table below shows what size pixel you should use to be "well-sampled", in terms of theoretical resolution, which is a function of f/#, (though atmospheric seeing has a big role in the final choice).  If you notice, that for any aperture, the f/# and pixel size determine if you are below, at or exceeding what the aperture of your scope can theoretically resolve.  So very briefly and simply:

 

f/#    Pixel size for matched theoretical resolution

4      2.40 microns

6      3.75

7      4.30

8      4.80

 

The reason you find most cameras with these common pixel sizes is that sensor manufacturers are not necessarily designing for astronomy, but all photography. That is why those sizes were chosen, since those are standard f/#'s common in photography.  In fact, if you look at the specs for a Canon sensor, for example, it will tell you the "Diffraction Limited Aperture" (DLA) that goes with that pixel size. (also below, which comes close to my calculations, though not an exact match).

 

I think I may have answered too much...    :/

 

Steve

Attached Thumbnails

  • ZWO_ASI294MM_BIN_2_Curves.png
  • diffraction_versus_sampling.png
  • Canon_Sensor_specs_EOS_60D.jpg

Edited by StevenBellavia, 28 June 2021 - 09:05 PM.

  • lowry_pt and druhela like this

#7 lowry_pt

lowry_pt

    Explorer 1

  • *****
  • Posts: 89
  • Joined: 07 Aug 2018
  • Loc: South of Indianapolis, IN

Posted 28 June 2021 - 09:24 PM

wow.  YOU more than gave an answer.  THANK YOU..  so essentially.  for BIN 1 ~~~Gain is a matter of desired exposure length. 

 

and then BIN 2.~~~ 120 or higher.  I am currently running Gain 200 for both actually~ ( another reading I found stated above 190 some lines or something). 

 

I really appreciate the explanation.  I think I wrapped my head around most of it.  I will reread it again.

 

Dawn


  • StevenBellavia likes this

#8 StevenBellavia

StevenBellavia

    Viking 1

  • *****
  • topic starter
  • Posts: 830
  • Joined: 11 Mar 2014
  • Loc: New York

Posted 29 June 2021 - 08:39 AM

wow.  YOU more than gave an answer.  THANK YOU..  so essentially.  for BIN 1 ~~~Gain is a matter of desired exposure length. 

 

and then BIN 2.~~~ 120 or higher.  I am currently running Gain 200 for both actually~ ( another reading I found stated above 190 some lines or something). 

 

I really appreciate the explanation.  I think I wrapped my head around most of it.  I will reread it again.

 

Dawn

Yes, the only "purpose" for a higher gain is to be able to do a shorter exposure.  This is no different from "regular" photography, such as being able to capture a ball deforming a tennis racquet, for example, with a very short exposure. 

But the total integration time required is essentially the same for all gains and exposures.

 

Gain and exposure are intimately tied to each other, and the best value for each "pair" should come from an optimization of SNR and Dynamic Range.  It is not only dependent on sky brightness, and f /#, but could be object dependent too.  Some objects need more attention to dynamic range (The Orion nebula, Andromeda galaxy), while others might need much more attention to SNR (Spaghetti nebula, Jones-1).

 

And of course, the highest priority needs to go to overall image quality.  There is no equation for that, and this is what makes this hobby so fascinating.

 

(:

 

Steve


Edited by StevenBellavia, 29 June 2021 - 08:56 AM.

  • druhela likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics