iso, asa and sensitivity to light

[dave92029]

I understand that iso and the old film asa scales are essentially the same.

They measure sensitivity to light. It appears that with each new camera we

demand higher iso (sensitivity) with less noise. What I'm finding odd is that

many correctly say that the new batch of P&S can't reasonably be used above iso

400 or the photo is too grainy / noisy.

 

I was trying to remember when I was shooting film, and it appears to me that

that same limitation also appied above asa 400. Is the really high iso numbers,

1600++, that are available and tested in most reviews, the result of the camera

maker's incorporating a very effective noise reduction program inside the

camera, or are the sensors able to sense marginal amounts of light without

producing "noise"?

 

Aren't some manufacturers claiming some really high iso capability? I remember

shooting at night with asa 1000 film. I had a low expectation for the quality

of the shot and rarely tried to shoot if that speed film was necessary. Why do

so many photographers need to shoot at 3200 or faster today? Was this

technology developed for the cameras in the spy satelites and now everyone

wants to shoot when there is marginal amount of light?

Just wondering what is driving this feature on new cameras?

 

Thanks for your insights

[martijn_houtman]

<p>

I always went black and white whenever there was little light available; I don't really like

noise in colour film, but find it somewhat 'charming' with black and white film. I even

pushed a lot of film for the sole purpose of getting a more grainy look (and more

contrast).

</p>

<p>

I think the answer to your (latter) question is: because we can. Digital enabled us to shoot

in less light and in the meantime have less noise as well. We sort of become to expect

more and more because of this. I think.

</p>

<p>

About the noise reduction versus sensor sensitivity: I do think noise reduction algorithms

have evolved a lot, but it's definitely the sensors that have become a lot more sensitive

without introducing more noise. And this will continue until we have near night-vision, it

seems (take the highest iso rating the D3 can do for instance).

</p>

[jo7hs2]

Dave,

 

P&S digital cameras have high noise at high iso largely as a result of their reduced sensor size. The sensor in a dSLR is much larger in physical size than the sensor of a P&S digital camera. But, many P&S digital cameras have similar megapixel numbers. That means that each site on the sensor has to be smaller, the spaces between the sites have to be smaller, and the circuitry has to be smaller to accomodate the P&S camera's smaller sensor. As all these things get smaller, they tend to get noisier.

 

dSLRs on the other hand, offer surprisingly decent high ISO performance. People are getting used to shooting heavily above ISO-400, something that in the days of film just wasn't always possible. The drive for low noise at high iso is largely a result of people using high iso more and more, now that they can.

[m_barbu1]

<p><i>Aren't some manufacturers claiming some really high iso capability?</i></p><p>In my experience, it's not just a claim. ISO 1600 on my EOS 20D is about what I could get with ISO 800 in film (and 3200 was about the quality of ISO 1600). On top of that, because the noise is a mathematically predictable pattern (unlike film grain), it can be <a href="http://www.picturecode.com/">removed via software</a> (albeit at the lost of some detail).

[Ed_Ingold]

I find ISO on my digital cameras to be the same as on my light meter and film cameras. The main difference is that digital is exposed for highlights like reversal film, whereas negative film is exposed for the shadows.

 

Digital noise does not have a "mathematically predictable pattern" except in terms of probability. It does have a maximum frequency, related to the pixel spacing, but is otherwise reasonably random in distribution.

[anindo]

The new cameras with high ISO and acceptable noise have made it possible to shoot what would earlier have been "impossible" images. For instance, I was glad for the ISO 3200 of my Canon EOS 1D Mark III while shooting hand-held at night at a crowded tripod-forbidden EDM (trance music) concert: I managed to get tight portraits of DJ Cark Cox at 500mm f/6.3, hand-held, something I would never have tried at a lower sensitivity!

 

That same week, I also shot New Year's fireworks on the beach, again hand-held, at ISO 3200.

 

Warm Regards

--

Anindo