Question about ISO and digital cameras...

[adegiulio]

Can someone explain to me how ISO works with digital cameras. I am a beginner in this whole photography thing, and have done my share of reading. Does the ISO setting on my D.Rebel just simulate the graininess of film? What do most people shoot at? do I really need to bother setting this?

Thanks for the help!

[Vegas Poboy]

First if you're a newbie to photography it would be wise to pick up a book on the basics of photography, digital has most of the same principles as film.
ISO/ASA is the speed rating and yes it would be wise to change the speed if you're shooting in manual or one of the priortiy modes. The higher you go the faster the speed the more grain you will pick up in your photos.
With film & digital one of my first settings is the ISO and that depends on the shoot.
Again it depends on the shoot when you make your settings, sports and low light 400/800, studio work 100 I barely uses 200.

[minicooper]

ISO is the sensitivity of the sensor. Like most things in photography, this is all about trade-offs. A higher ISO such as 800 will make the sensor more sensitive to light (ie, you will be able to use a relatively high shutter speed in low light). However, the downside of higher ISO ratings are that you get much more grain in your images. An ISO of 100 will have virtually no grain, but the sensor will not be so able to gather lots of light.

I hope this helps!

Tom
England

[arthurb]

Does the ISO setting on my D.Rebel just simulate the graininess of film? I really need to bother setting this?

To answer your questions, No, the DReb does not just simulate the grain. The grain is actually noise in the sensor. (In a film camera the grain is caused by noise in the film.)

The setting of the ISO depends on your expected result. If you are going to use the Rebel as a snapshot camera in the "Green Box" or other pre-programmed modes, in good light conditions, you may never need to change the ISO.

If you decide to experiment, the ISO setting allows you to decide how much noise you would accept in the resulting picture. It also allows you to use the camera to freeze action ot take long exposure photos for special effects.

For the average person using the DReb, they can't tell much difference between 100 and 400, but most can see the grain at 1600. In my opinion the noise at 1600 is not as bad as the noise in 1600 film.

In another thread, someone said that 1600 is useless, and that is just wrong. Most people take pictures for memories, not for show, and a slightly grainy picture is much better than no picture at all...

[chris.bailey]

Not much I can add that other have not. One thing I would say though is that using say ISO 1600 to simulate film grain (if that is what you want) is not, to my mind, all that successful. If I want to generate a grain effect I will still shoot at the lowest ISO I can and then add noise in PS i.e.

http://www.pbase.com/image/22414562.jpg

As well as grain, upping the Digital ISO (sensor sensitivity) also generates more visible coloured fringes around changes in contrast which when you sharpen up, can get quite nasty.

[nosquare2003]

Film grain / digital camera noise for reference:

http://www.outbackphoto.com/dp_essentials/dp_essentials_04/essay.html

[nosquare2003]

By the way, I agree with the author that some noises make a photo more natural looking sometimes. I have tried to remove my ISO1000 pictures (I'm using D60) with Neat Image. And I found that they are a bit "fake". I tried to add back some noises by Photoshop and they were better. (Or perhaps I'm not skillful enough in digital darkroom.) And I wish that my D60 has a ISO1600 setting which is as good as a Drebel...

[hmhm]

Boosting the ISO setting causes the sensor to apply additional amplification to the analog electrical signal produced after the sensor converts the incoming light to electricity. This effectively increases the sensitivity of the sensor to light, in the same way that faster film is more sensitive to light, but it has the downside that the noise is also amplified. (At least, this is how I understand it).

The noise in a digital image isn't really all that similar to film grain in nature, but we tend to associate them because they are both effectively sources of visual noise that tend to increase with ISO.
-harry