Noisy picture

I've been playing with ISO tonight, still not quite grasping how it effects what I take so you know there's still a lot to learn. But here's something I got with it:



I noticed that if I look at the original blown up to 100% there's quite a bit of grainy noise in the black. Not helping things is that EXIF does not tell me what my ISO setting was so I can't even go back and say "don't do this again"...

 

Not sure what your question actually is

I guess you either want to know what the effect of different ISO is and or what you can do to avoid the noise you observed.

Anyway, the ISO number basically gives you the sensitivity of the film to light (this concept was simply transferred from film to digital later). This means the higher the ISO the more sensitive your film or camera is to the light ... which means shorter shutter speed and/or smaller aperture become possible allowing for freezing the motion of fast moving objects and to get a large depth of field.
In very dark scenes (speaking of light here, not of mood ) you often need ISO greater 800 to take a picture. In bright daylight ISO 100 might be sufficient already (that refers to "standard" situations, numbers may vary depending what you actually want to achieve).

The drawback of high ISO is the noise you get. Both on film and from digital cameras. On film this is simply due to the film grain, which usually is larger for more sensitive film. In the digital world high ISO means that you get electronic noise from the camera's sensor and the amplifier coupled to it.

So, how do you avoid the noise? Just avoid high ISO Depending on the camera model, noise might be very significant already at ISO 400 (some point and shoot cameras) or 800-1600 (DSLRs). Of course everyone has a different idea of what he considers "significant" and what he thinks is acceptable in terms of noise.

Keep in mind that if you are a pixel peeper and watch your images at 100% on the screen, then the noise might be more annoying than in final print. Even in larger prints noise is often much less annoying than on the screen.


However, often you might run into the situation with low light, maybe also fast motion, where you need high ISO and you cannot avoid considerable noise.
There are a lot of possibilities in post processing though. You can significantly reduce image noise without loosing too much image detail. There are some commercial products out there like NeatImage, NoiseNinja and many more which all do a more or less good job.

hope that answers part of your question

Cheers,
Alex