Every Tuesday, I bring you a tidbit of information to help you improve your images, learn more about the technical aspects of photography and generally just “talk shop”. This week is about understanding how ISO/film speed works.
Have you ever noticed that some of your pictures have more noise (ugly colored speckles) than others? What’s up with that, right?
ISO is what’s up with that
ISO (also known as film speed….even though many of us don’t use film anymore) was created by the International Standards Organization in order to establish a standard way of identifying how sensitive a roll of film is to light. Film with an ISO of 200 is half as sensitive to light as film with an ISO of 400. ISO 100 film is a quarter as sensitive as ISO 400 film. Great, you say, so what does that mean in the real world? Well, it means that the higher the ISO number, the more sensitive the film is to light….which means, all other things equal like aperture and shutter speed (definitions found here), you need half the light at ISO 400 that you do at ISO 200 to create a properly exposed image. The higher the ISO, the less light you need.
Awesome. So what?
Even though film is going the way of the dinosaurs, it’s still an important concept to know. Our digital cameras are still sensitive to light…in microchip form. So if you’re taking a picture in low light, your digital camera is going to automatically kick up the ISO to increase the sensor’s sensitivity to light (or, if you’re an SLR user and it’s not in automatic ISO mode, you have to adjust the ISO yourself).
And the problem is?…….
Well, there’s one major snag. The higher the ISO you use, the more noise that appears in your image. Now I’m not going to get into why because, frankly, Michael (my dear hubby) has explained it to me two or three times already and I still don’t fully understand it enough to explain it properly to you all. Suffice it to say that a higher ISO=more noise and that, in most cases, more noise=not good. How’s that for a simplistic explanation?? 
In order to prevent that noise from occurring, you either need to a) dial down the ISO on your camera or b) if you can’t do that, add more light (turn on a light or your camera’s flash) so the ISO automatically goes down.
If you absolutely can’t avoid high ISOs and noise, and you absolutely must use the image you took, there is hope. There are several programs out there, some better than others, that will remove the noise from the image after you’ve created it (we use NoiseNinja). There are drawbacks to the programs and it’s not ideal, but it can save an otherwise unusable image.
Happy shooting from Vantage!
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If you’re curious, the reason higher ISO = higher noise is that to increase the sensitivity of the camera sensor, the camera has to pump more electricity through it. The higher electricity causes interference between the individual photosites (pixels on the sensor), which looks like “noise” in the final photo.