AP pixel overflow question

[lsintampa]

Not sure if this is the correct forum to ask this, but....

I've been doing some reading about sensor pixels and how they capture various types of photons. These discussions get into pixel depth and that (as I understand it) is how many photons a pixel can hold before it is full - or over full.

Further reading on AP imaging, I read about 5 minute subs, 10 minute subs, etc.

Now I try to put the two pieces together and ask this question: how long of an exposure can you take (say with a mid-range DSLR) before you exhaust that sensor's pixel depth.

Not sure if my understanding is totally correct, but if I'm even close to understanding, then the question stands.

At some point if you leave the sensor open - it will just overflow and every pixel will look the same - no? Or is it first in last out type of thing - so you really can't overflow them???

Confused in Tampa.

[JayTee]

How quickly the pixels fill-up (saturate) is entirely dependent on how bright the target is. Jupiter will saturate the pixels in one second whereas M104 will take approaching 5 minutes. So, exposure duration is usually limited by how much light pollution you have not how bright / dim your target is. Only when you go to a dark site would you even consider full well depth of your pixels and even then you shouldn't because it can be fixed in post-processing.

Cheers,
JT

[lsintampa]

How quickly the pixels fill-up (saturate) is entirely dependent on how bright the target is. Jupiter will saturate the pixels in one second whereas M104 will take approaching 5 minutes. So, exposure duration is usually limited by how much light pollution you have not how bright / dim your target is. Only when you go to a dark site would you even consider full well depth of your pixels and even then you shouldn't because it can be fixed in post-processing.

Cheers,
JT

Thanks for that!

So then as a follow-up, when a pixel is saturated and it is still exposed, does that change the value (contribution to the data) or is that pixel still viable?

What I'm trying to understand is what happens if you over expose the target, regardless of light pollution etc., To the overall value of all the data the sensor took in.

IE, 5 minute subs on Jupiter, using your example, what would happen???

[JayTee]

In the case of grossly overexposed large objects (eg Jupiter), you get nada! Much like when you overexpose the moon - it turns into a white blob! But with stars, these are point sources of light and typically work on a very small array of pixels, even as few as one pixel. So the "overexposing" is not quite the same, plus we typically are imaging the fainter than star stuff (usually) so the handful of saturated stars is not much of an issue.

Theoretically: Once saturation occurs at a charge collection site (a pixel), the accumulation of additional photo-generated charges (photons) results in overflow, or blooming. The excess electrons will overflow into adjacent pixels. With stars, this blooming, which makes the star look bloated, can be addressed in post-processing.

Cheers,
JT

[lsintampa]

Awesome feedback. Thanks.

[Graeme1858]

Not sure if this is the correct forum to ask this, but....

I've been doing some reading about sensor pixels and how they capture various types of photons. These discussions get into pixel depth and that (as I understand it) is how many photons a pixel can hold before it is full - or over full.

Further reading on AP imaging, I read about 5 minute subs, 10 minute subs, etc.

Now I try to put the two pieces together and ask this question: how long of an exposure can you take (say with a mid-range DSLR) before you exhaust that sensor's pixel depth.

Not sure if my understanding is totally correct, but if I'm even close to understanding, then the question stands.

At some point if you leave the sensor open - it will just overflow and every pixel will look the same - no? Or is it first in last out type of thing - so you really can't overflow them???

Confused in Tampa.

Here's a pixel tutorial I found recently whilst researching Flat Frames. It didn't tell me everything about Flat Frames but a good tutorial natheless.

The answer to your question is there with pictures too. When the pixel well is full, its adc output is maximum (saturated), it stays that way until it's emptied when the shutter closes.

https://cloudbreakoptics.com/blogs/news ... xel-part-1

Regards

Graeme