ZWO ASI174 Exit stage left? Or right?

[Rusted]

Hi,

A very simple question: The answer may not be so simple.

Why does altering Gain or Exposure, in SharpCap, make changes of brightness travel right across the computer screen?

Why doesn't the whole screen become lighter, or darker, evenly all over?

With the screen apparently edge lit, from the right side, it often requires a much smaller frame size [Capture Area] to exclude the offset brightness.

Is this normal?

[Adam J]

15 minutes ago, Rusted said:

Hi,

A very simple question: The answer may not be so simple.

Why does altering Gain or Exposure, in SharpCap, make changes of brightness travel right across the computer screen?

Why doesn't the whole screen become lighter, or darker, evenly all over?

With the screen apparently edge lit, from the right side, it often requires a much smaller frame size [Capture Area] to exclude the offset brightness.

Is this normal?

I think you might be confusing a few different concepts here.

The screen is not getting brighter with gain its the image that the screen is displaying that is getting brighter, gain is just acting within the CMOS chip to cause lower electron charge levels on the pixels to be converted into larger digital values. In doing this you reduce dynamic range but because of there the gain is acting in the digitization process and because of something called quantization noise higher gain also results in lower read noise.

Exposure (assuming you mean exposure length as opposed to digitally lightening the image) is going to make the entire image brighter because even the background of the image is going to be at an non zero level even when you think it is just empty space, this being as a result of light pollution and natural sky glow. If its exposure in terms of digital processing then its just a linear stretch to the 16bit image causing every pixel to be presented at a higher value.

The only thing that will effect the brightness of one part of the image more than another is a none linear stretch, also known as a curves adjustment.

I think when you say Edge Lit you are talking about the brightness on the right hand side of the IMX174 sensor in your camera, this is nothing to do with the screen it is cause by something called amp glow and it affects many CMOS type sensors. SO this is normal and to removed this you need to used dark frame subtraction. If you search the forum for dark frame subtraction or look in the sharp cap user guide you will find what you need.

Hope this helps.

Adam

 

[Rusted]

Thank you very much, Adam, for your very thorough response. You have raised some fascinating issues:

Firstly, I am primarily a solar [and lunar] imager using a 6" or 7" refractor. So there's never [usually] any lack of light.

Until now, I have tried to keep [SharpCap] Gain as low as possible. Often set to Zero even with maximum 2ms exposures using the '174.

Then I changed a vital solar filter component. Which required much more light than before.
So I opted for much higher Gain settings. Just to keep exposures as short as possible.
I imagined [in my ignorance] that the two settings were a simple see-saw. One goes up as the other goes down. Ignorance truly is bliss!

My thinking was that thermal agitation of the image would be minimized by using the shortest possible exposures.
Probably an overly-simplistic response through a complete lack of [your] expert knowledge. Gain bad. Exposure acceptable.

Now you have raised the spectre of loss of dynamic range I shall have to seriously rethink my video capture settings.
It seems I must limit Gain as much as possible at the expense of rather longer Exposures. Certainly worth conducting some trials.

Meanwhile, my "asymmetric lighting" problem will probably respond to Light Frames/Flats rather than Dark?

Thanks again.

[Rocket Stars]

I can recommend playing with the sensor analysis i sharpcap! 

There is also a feature in the histogram funktion. Click on the brain to get recommended settings. Good lerning tools! 

I like it a lot

[vlaiv]

@Rusted

You are doing solar work. You have very bright target regardless of any filter components that might dim it a bit.

Your primary concern should be - exposure length, because solar work is again lucky planetary type imaging. With planetary / lucky type imaging you want to freeze the seeing. Exposure length depends on something called coherence length and coherence time.

For most part - that means exposure lengths of about 5-6ms when doing planetary. Only in very best seeing you can go with 20-30ms exposures, but that is rather rare. Planetary imagers struggle to get enough signal in such short exposure, but you should have no issues. You already have low enough exposure length with 2ms to beat the seeing.

Next important thing with planetary type imaging is read noise. If read noise is zero - there is no difference in single exposure of one minute or thousands of short exposures all totaling to one minute (difference in SNR) - as all other components are time dependent and add up the same. Only read noise is per sub - and more subs you have more times you add read noise.

For this reason, best planetary cameras have fast readout and low read noise.

Gain setting changes both full well depth and read noise. Unless you are saturating in your exposure - you should not worry about full depth / dynamic range in planetary imaging In fact, you don't have to worry about it - period. If you saturate - just reduce exposure length.

This is very important graph for you - it shows that read noise is the lowest at about Gain 300. Dynamic range is still high enough at 8bits (for planetary imaging as you will be stacking hundreds or thousands of subs).

In the end, let me add that you should do proper calibration of your recordings. This means darks, flats and flat darks. Go crazy with number of subs there - hundreds of them (provided that you have strong enough flat panel and your flats are short - even one second flat will take only 15 or so minutes to record both flat sequence and flat dark sequence in hundreds of subs).

Use PIPP to calibrate your ser with all of those (it supports loading of ser files to do calibration) and export calibrated ser without much processing ( and then continue to AS!3).

[Rusted]

Thank you vlaiv for your very useful and thorough response.

Hopefully it will help to improve my results from making much better informed decisions. 
Today I started using Mono16 and SER files for the very first time. I have always avoided both until now. 
I have not tried flats yet but solar imaging experts have suggested placing a translucent [not transparent] bag over the objective for this.
I've used PIPP before but not routinely in my normal processing sequence. I shall have to give this a try too.

Thanks again.

[Rusted]

12 hours ago, Rocket Stars said:

I can recommend playing with the sensor analysis i sharpcap! 

There is also a feature in the histogram funktion. Click on the brain to get recommended settings. Good learning tools! 

I like it a lot

Thanks.

I had a look at both of these, this morning, but they seem more oriented towards night time imaging.
Further study will certainly follow in the hope of greater understanding of their potential.

[Merlin66]

I use FireCapture for all my solar imaging.

With the ASI 174MM is set the gain to 189 and the gamma to 50. Vary the exposure to set the histogram right hand edge close to 80-90%. Take SER video, 500-1000 frames and process in AS3! start with the "best" 50% then try "best" 25 % - see if you can notice any significant difference (will depend very much on your local seeing and focusing abilities)......

ImPPG to do some "smart" sharpening. That's the basics......

 

[Rusted]

Thanks for those suggested FireCapture settings.

Rant/

From increasingly, distant memory I couldn't use FireCapture because it had no facility for high res. screens. [Years after such screens became popular!]
Everything on the screen was sub-microscopic and largely consisted of totally inscrutable, alien symbols. They were utterly meaningless to me!

I tried readjusting the screen res. to match this one app. but don't have enough brain cells left to learn a whole new language of hieroglyphs.
This did not help much either. Because now the drop down, text size completely mismatched the alien symbols!

Just finding the correct symbol for switching between automatic night screen and [desired] daylight viewing [for solar imaging] took me several, completely wasted days!
I needed increased clarity just to be able to see the silly symbols with my strongest reading glasses. Never again! Life is already too short and rapidly becoming shorter! 

SharpCap speaks human and is as user-friendly as one could possibly wish for. It runs on autopilot as far as I am concerned.
And, I can read everything on the screen and recognise the meanings of the [very few] helpful symbols completely without effort.

Rant over.

[johninderby]

My solution for Firecapture and it’s micro text. 

Edited April 6, 2020 by johninderby

[Merlin66]

Try the latest...

I don’t experience any problems with FireCapture......

 

[Rusted]

I'll take another look. 

[Jonk]

23 hours ago, Rusted said:

I have not tried flats yet but solar imaging experts have suggested placing a translucent [not transparent] bag over the objective for this.

When I learnt how to do solar flats, I was told to point at the sun so the whole sensor is covered, and defocus so you get an even illumination.

Worked for me and it was really easy.

[Rusted]

FireCapture hasn't changed at all. Still hopelessly unfriendly!

Dark red with microscopic text.  Seriously?

[Rusted]

14 minutes ago, Jonk said:

When I learnt how to do solar flats, I was told to point at the sun so the whole sensor is covered, and defocus so you get an even illumination.

Worked for me and it was really easy.

Thanks Jon. De-focusing means touching the telescope and losing the target.

Bagging it with a thin, translucent bag can be done without touching the telescope.