Unity / global gain.

Tech@ZWO

denababy Unity Gain is 100.
If you refer to the global gain in the ASIAIR APP - Autorun or Plan mode settings, it lies on the gain value you set in the main camera settings.

Corsair

Tech@ZWO

Can you please go here - https://bbs.astronomy-imaging-camera.com/d/15898-asiair-v21-has-been-released/164 - and make a statement regarding support for the ASIAIR.

It's been a while since we've had an update on progress. Would be nice to know the app is still being developed.

Tech@ZWO

Corsair Sure, i will reply there later.
Thank you for your support

Kevin_A

Unity gain is 100? Huh… nope! The 2600 cannot actually achieve unity.
Note that the IMX571 sensor doesn't have a real Unity Gain mode. Unity Gain is where 1 electron gives rise to 1 ADU. For this camera with a full well of 51100+ electrons, you can not reach the full 16 bit range of the A/D. The sensor cannot reach the point at which 1 electron equals 1 ADU. At 0 gain it only achieves 0.7 e /adu and less at gain 100 where the HGC kicks in.

Tech@ZWO

Kevin_A
My apologies, I confused unity gain and the gain value that turns on HCG mode.
For ASI2600 Unity gain value is -23/24 after the extended full well mode is on.
Usually, we recommend setting the gain value that is turned on HCG mode, which is 100 on ASI2600MC.

w7ay

Looks like ZWO cannot even read their own data sheets. This is from their ASI2600 page:

Their answer is completely bogus.

Do you see any gain setting that will give an e-/ADU of at least 1 (unity)? Kevin is correct, the best you can get is an egain of 0.75 or so.

The way things work is this:

The electrphotons (e-) arrive at the sensor as discrete electrons. There is no such thing as registering an intensity level of 1.5 e-, for example.

So, the intensity levels that you can recieve from your star are 1e-, 2e-, 3e-, 4e-, etc.

Lets say the egain is set to 0.5 e-/ADU (== 2.0 ADU/e-), then the star with 1e- will show up as 0 ADU, the ones with 2e- will show up as 1ADU, the ones with 3e- will show up also at 1ADU, etc.

So, what you are losing is the fine scale intensity resolution when you cannot achieve the magical unity gain value.

That being said, I wouldn't loose sleep over it; multiple subframes will make up for it.

Check out the dynamic range of the ASI6200 (very similar behavior as the ASI2600) from some images I took to test the new filter recently. There seems to be enough dynamic range (especially with Pleides and the Running Man nebula):

https://bbs.astronomy-imaging-camera.com/d/16893-asi6200mc-antlia-triband-rgb

Chen

Kevin_A

I have settled on Gain 100 for dim targets and narrowband and Gain 0 for bright targets and broadband as the noise is so low that at Gain 0 which is the closest to unity, the images are equally nice if not a bit better. That is very target specific and I always keep my subs at 180s for broadband and narrowband in my B4 sky. This is Gain 0 at 5 hours on a bright target.

Corsair

Oh. I got a bit mixed up with the graphs.

I was reading off the graph at the bottom of this image - https://astronomy-imaging-camera.com/wp-content/uploads/graph-of-2600mc-pro.png. The being said they do say:

The ASI2600MC Pro boasts excellent performance with a dynamic range of up to 14 stops. When the gain value is set to 100, the HCG high gain mode is turned on. We’re not saying it’s magic…but we’d like to think it is pretty close. With the HCG-mode turned on, the readout noise is greatly reduced, and the dynamic range is basically unchanged. To improve the data quality, it is recommended to set the gain to 0 or gain 100 during deep-sky imaging.

I guess because with my 294MC Pro - https://astronomy-imaging-camera.com/wp-content/uploads/294-Gain-RN-DR-FW-vs-gain2.jpg - they recommend setting the gain to 120/121 even though unity gain is at 117.

Kevin_A

Corsair I use gain 100 for most of my imaging. I use gain 100 for all narrowband targets where I am using a filter like a l-enhance or very dim targets. If Iam shooting without a filter or with a l-pro broadband filter, I use gain 0. If I am shooting a bright target like M31 I use gain 0. Both gain setting produce very little noise and if you just use gain 100 then just cut back on exposure lengths when shooting bright broadband targets.

Kevin_A

Tech@ZWO i use Gain 0 on broadband targets that are very bright when using fast optics as it helps retain star colour and allows for a longer sub exposure so I can reduce the number of subs… so it is useful. HGC mode is overall the best setting for 90% of targets and best fir narrowband targets using filters.

Byrdsfan1948

Not any attempt to hijack this thread but as someone relatively new to this very complex hobby I still have many seemingly very basic questions regarding subjects new to me the last couple of years.

This particular thread is one of them. Could anyone point me to any link that might explain as simply, and clearly, as possible what the differences are between Unity, and Global Gain, as well as the pro and cons in their application within our hobby?
This thread has provided some helpful information but as in most threads, also only left me with more questions as well.
Thanks for any help Al

w7ay

Byrdsfan1948 Global Gain

Hi Al,

"Global Gain" is just an ASIAIR thing. Try not to rememeber it since you will one day eventually be leaving ASIAIR for something better and more reliable, and more documented.

"Global Gain" in ASIAIR simply means "use the gain value that is selected in the Main Camera Settings window." That is another of ZWO's attempts to make it simpler for the 1,2,3 morons, and at the same time confuse everyone else.

A sensor works by having a "photo-electron" (denoted by e with a minus sign as a superscript; and in ASCII text usually written as "e-") hit a photodetector and producing an electrical current. This photoelectic effect, is one of the two (the other one mentioned in the Prize is Brownian motion) that Herr Einstein received his Nobel for (he did not receive one for General Relativity).

Since photo-electrons are discrete quantas (you cannot have 1.5 photo electrons, for example), the currents can also only take discrete values, i.e., n Amps, 2n Amps, 3n Amps, etc. (n is verrry small).

The currents from the photodetector are fed to an A/D converter (into units called the ADU) after applying an analog gain stage ("DC amplifier").

The A/D converter measures discrete levels. The optimal "gain" is when the n, 2n, 3n, ... are perfectly aligned to the A/D converter's discrete levels. This is called "Unity Gain." If the analog gain is too high, many of the A/D converter levels are simply not used (lose resolution). If the analog gain is too low, a of the the "n" steps are lost (lose dynamic range).

Chen

Byrdsfan1948

w7ay

Ahh hello my friend been a while !!

So first thanks for the response.. I'm still probably a bit unclear but to summarize what I got from your attempt to educate the village idiot I sort of conclude this:

Ignore the term Global Gain......... Period!! But when you say it simply means Global Gain is the actual gain value that is indicated in the setting windows, I assume you essentially mean if I were to set my gain to say 160 that is the "Global Gain" used for those images eventually produced at that setting.

Many thanks for the detailed explanation of Unity Gain........ NOW I get it!!! Mission accomplished!

Ahh on a different note. As far as Dr Einstein and why he hadn't received a Nobel Prize for either his earlier relativity theory's Special 1905, and General 1915, I have my own unproven theory. Both theory's were so radical and Einstein himself so young and at the time still somewhat "unknown" that it may have been a case of he was just too far ahead of his time. Plus it wasn't until the famous eclipse of 1919 ( believe WW1 got in the way of an earlier 1917 opportunity ) where one of the predictions of General Relativity could be tested...... And as an eventual result proved that Einstein was correct...... Immediately leading to instant super stardom !! Come 1921 and his Photoelectric effect and along comes the long over due Nobel. ALL QED if your an Einstein !!!! Al

w7ay

Byrdsfan1948 But when you say it simply means Global Gain is the actual gain value that is indicated in the setting windows, I assume you essentially mean if I were to set my gain to say 160 that is the "Global Gain" used for those images eventually produced at that setting.

If you set the gain the the Main Camera settings to 160, then selecting "Global Gain" in AutoRun will simply just use 160 also. Might as well do it yourself each time you need to set a camera gain. It is for the utter idiots.

As far as Dr Einstein and why he hadn't received a Nobel Prize for either his earlier relativity theory's Special 1905, and General 1915

Actually, you will find that it is still not proven for sure. SR is the thing that most people know what relativity is all about (time dialation and such), and taught to every Physics undergrad. (I am EE, but do belong to Sigma Pi Sigma from back in 1969).

I had taken two GR classes in grad school, one from the Math departent (given by M. M. Schiffer himself) and the other from the Physics department. Neither made me understand the universe better :-). Just a bunch of Tensor Calculus that attempts to model the universe :-).

Chen