Full well, an issue??

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Taipan
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Full well, an issue??

Post by Taipan »

A question. Is the full well related to the dynamic range?
My camera has a fullwell at 25880 at gain 0. And the FW is 11003 at Gain 70
Because of a function in the camera the noice is reduced at gain70 and the dynamicrange is almost the same as at gain 0.
Only the full well is still reduced at Gain70.
Now the question. If there is less noice att gain 70 and the same dynamic range. Should i bother about the reduction of the Fullwell?? Or is the fullwell more important than tha lower value of readout noice??
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Re: Full well, an issue??

Post by Taipan »

Oh. The camera is the player one Apollo-M Mini.


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Re: Full well, an issue??

Post by marktownley »

I always think the same about my ZWO cameras as they always provide this information. I think the best thing to do would be take a series of exposures at these different parameters and see if there is any noticeable difference.


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Re: Full well, an issue??

Post by rsfoto »

Hi,

Interesting question but what always bothers me here is the infamous Gain. Perhaps I am allergic against GAIN in the cameras :lol:

What I understand about the well capacity is how many electrons fit in the well and therefore when my Gain is set at 0 then in this case the camera can collect till it is full 25880 photons, ¿ correct ? and not only one well but all wells will collect this amount more or less and as light travels in a straight way until it hits something then some pixels will collect less photons because at that part less photons were emitted and on other parts it will collect all 25880 as that part of the object was very brght or even white.

This means 25880 is white and 0 is black more or less. The this values are converted to values from to 12 bit values being white 4096 and black 0 and that fits the chart e-/ADU

ApolloMini_etoADU.JPG
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which more or less means 25880 / 6,318 = 4096.23 as white and 0 / 6,318 = 0 as black.

Now you crank up the gain to 400 as in the chart and the well will say I am full when it has reached 256 photons and this will artificially converted to 4096 shades of grey, but this are not real photons you got in the well.

When you crank up the gain to 70 you will have 11003 photons in your well, yes same Dynamic range as 0 gain.

In all cases you get allegedly 12bit colour depth but this is due to a interpolation the camera makes ...

Is this what I want to explain more or less clear ¿?

That is the reason I do not use gain. This would be the same as if I fill a 10 liter bucket with 25 milliliters and then I try to sell you the 10 liter bucket telling you, here is a bucket with 10 liters of water ...

IMHO :o
Last edited by rsfoto on Tue Apr 26, 2022 5:04 pm, edited 1 time in total.


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christian viladrich
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Re: Full well, an issue??

Post by christian viladrich »

Hi,

The dynamic range is the ratio between the Full Well capacity and the readout noise. This is not a characterictic very important for solar imaging. One of the very few situations where dynamic range is important is total solar eclipses where the dynamic range between the inner and outer corona is simply huge.
In "usual" solar imaging, the dynamic range is rather small (compared to the dynamic range of present cameras).

The important characteristic for solar imaging, is the maximum signal to noise ratio (SNR). We have:
SNR max = square root of Full Well capacity
So a larger FW means a larger SNR max.

A large SNR max means you can apply wavelet/unsharp mask/ deconvolution (or whatever filters) without having a big amount of noise coming up.
You can increase SNR max by stacking frames, and/or by using a camera with a larger SNR max.

Using a camera with a large SNR max, you need to stack less frames (which improves resolution).

But if you want to actually get this large SNR max, you need to use the camera with the minimun gain value (see full well curve). This is why it is recommended to use minimum gain value for solar imaging.

This is true only as long as you have plenty of light (i.e. white light imaging with a solar wedge), which allows to keep short exposure times (< 5-10 ms). When there is not enough light, you need to increase the gain in order to keep exposure time short enough.

At the end of the day, you don't care about the dynamic range of the camera, but you do care about SNR max (meaning you care about the Full Well capacity).

This is why the IMX174 is so good for white light imaging, with a SNR max of 7.5 bit (compared to 6.9 bit for the IMX 178 and 290).

The IMX432 with its 100 000 e- FW (thanks to its 9 micron pixels) has a 8.3 bit SNR max, which is even better.


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Re: Full well, an issue??

Post by Taipan »

I don't need to use gain to get a good exposuretime. 1,79ms at Gain 0.
The reason i asked is because of the readout noice.It's much lower at gain71. But thats not an issue i guess.
And the dynamic range doesn't give me better proms from the dark sky when i do exposure of the limb? I only take one exposure fot both..

Also post a picture of the sun from 23/4. First light with the Apollo-M Mini. Used a singelstacked Lunt LS60MT B600
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Re: Full well, an issue??

Post by christian viladrich »

Hello,

The noise of solar images is dominated by photon noise. Readout noise is negligeable compared to photon noise. This would be a different story for planetary imaging.

The dynamic range of solar images is not huge. For example, the sky in your image is not black, because there is a lot of instrumental diffusion. The faintest detail you can capture is not limited by the dynamic range of the camera, but by the instrumental diffusion. So, there is no need to have a camera with a very large dynamic range.

Still, you need a camera providing a large max SNR.


Christian Viladrich
Co-author of "Planetary Astronomy"
http://planetary-astronomy.com/
Editor of "Solar Astronomy"
http://www.astronomiesolaire.com/
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