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AMG Jun 8, 2004 8:50 AM

Hello, this may be an easy question, but I still haven't found an answer. ISO when it comes to film is quite simple. It tells the camera how sensitive that film is to light and the camera uses that data to calculate the best shutter speed and aperture based on it's metering. Digital cameras are simlar in many ways except one, there is no film. When you manually change the ISO in a digital camera, what exactly are you doing. There is no film, just the sensor which has is a fixed item.

So my question is for some explanation. Is it just a trick so that people think they have certain control. If you use the same shutter speed and aperture for the same pics with different ISO's will it be that the higher ISO will be over exposed. If not, then what does it do.


Jenni Jun 8, 2004 8:58 AM

Not to burst your bubble, AMG, but I have no idea what the answer is.

However, I would also LOVE to know! I have fiddled around with the ISO setting on my Olympus C-700 many times, either picking 100, 200, 400, or 800, but I really have no clue what I am doing. What do each one of those numbers mean?

If anyone could help us out, that would be super!

Thanks as well!

photosbyvito Jun 8, 2004 9:06 AM

ok..i'll explain wat i know about it....

i have no idea wat the sensor itself is doing when you change the ISO, but i do know how it effects the picture.

Changing the ISO up, makes the picture brighter, from 50-100 and 100-200 and 200-400 and 400-800 are full changing the ISO from 50 to 100 will have the same effect on exposure as if you changed the arperture from f8 to f4....

hope this helps :)

AMG Jun 8, 2004 9:23 AM

I figured that, but is it changing the sensor's sensitivity to light I wonder. You see in film, I prefer 100 as long as it is bright enough outside, I just find the colors rich and the picture very clear. I wonder what woukd yield a better result, increasing the ISO and lowering the exposure. It just seems to me that there shouldn't be an ISO setting at all, only shutter speed and lens opening...

photosbyvito Jun 8, 2004 9:27 AM

well...i'm not sure that the digital world has caught up to film in the ISO department...except maybe the expensive SLRs....

Mikefellh Jun 8, 2004 9:49 AM

Basically, digicams have an ISO rating indicating their level of sensitivity to light. When increasing the ISO the output of the sensor is amplified, so less light is needed. But that also amplifies the undesired noise which creates grainier pictures, just like in film photography but for different reasons. It'ss like turning up the volume on a radio with poor reception. Doing so not only amplifies the desired signal, but also the undesired static or "noise" as well.

AMG Jun 8, 2004 10:13 AM

ok thanks a lot, so one may be better offto capture with as little noise as possbile and edit insoftware. I had a feeling it may be something like this, thanks for clarifying

slipe Jun 8, 2004 10:53 AM

AMG wrote:

ok thanks a lot, so one may be better offto capture with as little noise as possbile and edit insoftware. I had a feeling it may be something like this, thanks for clarifying

Maybe there is something lacking in my technique, but it doesn't work that way for me. It seems that when I shoot at a lower ISO and pull the shadow detail out of the weeds I induce at least the amount of noise I would have gotten had I just shot at the higher ISO. If I want to make a big print or blow up a small section I just apply Neat Image.

ISO seems to work about the same way as film. Increase the sensitivity of the CCD and you get more noise. Increase the sensitivity of film and you get more grain. I have a film scanner and scanning ASA 400 negatives gives worse grain than the noise from ISO 400 in my digitals. I really need Neat Image to print them larger than snapshot size.

I think a DSLR does better at higher ISO than most film. Wouldn't bet my house on that though. Part of that for me might be that film scanners accentuate the grain. Film might compete equally if you stay within the photographic process.

Setiprime Jun 8, 2004 11:29 AM

Slipes got it right -

The changing of the ISO rating is the same effect and result that you would get by changing your film type in cameras.

The ratings are closely equivelant to the old film standards. Generally speaking, in a DSLR, you can shoot at higher ISO ratings to help get your shutter speeds within acceptable ranges for your subject. At higher ISO, you do get more noise (grain), however in post production this can be neutralized to a great degree.

In Point & shoot cameras, the noise is much more noticeable above ISO 100. This is part of the trade off for getting "sharper" shots in a P&S.

Of course theres more to it than that - but thats for other threads to discuss.

Good Shooting - Jon F

Mikefellh Jun 8, 2004 12:52 PM

You do what you can to get the shot, and clean it up later.

There are programs out there that are specifically designed to get rid of this type of noise, and some are even FREE:

I was at a school reunion and I had to use ISO800 to get a few shots where no flash was allowed...yes they were noisier, but it can be cleaned up and I got the shots.

Yes, it's better to shoot lower ISO to reduce noise, but it's nice to know it's there when you need it.

And the added benefit of ISO on digital, you can have a different ISO for every shot and not have to fiddle with unloading and reloading different films (or for the pro, carrying multiple cameras each loaded with a specific film speed).

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