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Impact of exposure time on noise

Author	Post

Posted by Eric: Fri Dec 7th, 2012 05:31

1^st Post

I have seen the light! ....maybe?

Having read an article in AP about the impact of noise on a camera's dynamic range and hence its tonal range I was surprised!

After years of using digital cameras I never realised, the longer the exposure...the less noise. If fact, if asked, I would have said the reverse.

It's logical when you consider exposure time shifts the signal to noise ratio in favour of the former....but I had never considered the significance of this.

Somehow I have always interpreted the higher than expected noise levels of photos taken at low ISO, in dark interiors, to be due to the necessary long exposures. It now seems that its nothing more than underexposure.

I think?:baffled::baffled::baffled::baffled:

Have a read at this....

http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/noise-p3.html#bitdepth

PLEASE NOTE
I have only read a couple of sections...I need a rest to digest whats been written...then I will continue further down.

This note is in case some more scholarly person reads to the bottom before I do.... and finds a contra argument.

:rofl:

Oh Lord...just read some more while the wife is having root canal. Not sure I wouldn't prefer to trade places...as this is more confusing and head banging.

____________________
Eric

Posted by Squarerigger: Fri Dec 7th, 2012 07:46

2^nd Post

Thanks Eric, my eyes went crossed, my head was tilting, and for a brief period of time I thought my head was spinning. :rofl:

Didn't get very far in the study. Will leave it to you, Ed and Robert to sort out. But thanks for sharing.

____________________
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Gary

Posted by Iain: Fri Dec 7th, 2012 08:08

3^rd Post

Phew, that is a bit to heavy for me. I'll leave it until someone translates it. :rofl:

Posted by Eric: Fri Dec 7th, 2012 14:49

4^th Post

Iain wrote:
Phew, that is a bit to heavy for me. I'll leave it until someone translates it. :rofl:

The first time I read it, by the time I got down to the section on noise v dynamic range I was suffering subject blindness.

I think it's saying that while trying to expose for the highlights, we should understand that underexposing to protect highlights may introduce more noise.

I also think that if long exposure means less noise, it sort of supports using lower ISO and longer shutter speeds in preference to high ISOs and fast shutter speeds????

:baffled:

____________________
Eric

Posted by Robert: Fri Dec 7th, 2012 16:26

5^th Post

Very interesting Eric, thanks for posting.

I cheated... I went to the bottom line and skipped the techie bits, well, I did read some of it but the author was showing off with some fancy words that are far to long for me! :lol:

The bottom line says, if nobody got there... Pixel size doesn't matter too much, sensor size is much more important. Well I tink we knew that but not perhaps why. Larger sensors gather more photons from the same scene than a small sensor, that's it in a nutshell.

I was interested in a technique in the supplement which uses HDR to combine two images, one taken at ISO1600 the other at ISO100, the result is interesting.

I WILL read it all but not tonight, I have been outside all day and my mind is almost a numb as my fingers. I have bookmarked it.

____________________
Robert.

Posted by jk: Fri Dec 7th, 2012 16:31

6^th Post

Well I've had a long day fixing and updating computers.
So........ I have always thought that there are several factors that influence the digital noise in an image.
1. Length of exposure - longer worse than shorter.
2. Sensor heating due to longer exposure usage.
3. ISO different from the optimum ISO value of the sensor.
4. Bad DAC design.

I'll try and read the article when I feel less tired.

____________________
Still learning after all these years!
https://nikondslr.uk/gallery_view.php?user=2&folderid=none

Posted by blackfox: Fri Dec 7th, 2012 19:35

7^th Post

read through some of it ,the only comment i can really deduce is that he's taken so long writing it up ,that the cameras used in the equation are virtually obsolete .things really do move fast in this game and you have to keep a couple of steps in front :baffled:

Posted by blackfox: Mon Dec 17th, 2012 14:13

8^th Post

one thing i will add and commenting only re my own limited knowledge ,nikons are far far better at handling image noise than canons ,i really love the smoothness that i,m getting out of my old d300s ,far better than any previous camera ,just up loaded a wren to my gallery taken in really bad light and totally love it

1st new

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