So…Bigger is better, right?
Today I have a shot that is probably my new favorite to show you. It is a great example of photographic luck, in that I came around a curve, liked what I saw, hung the camera out the window, and popped the shutter without even looking. Generally, what you see here is what I got. I tweaked it a little bit but only in the Microsoft Office Picture Manager—the only tool I had available when I went to do the edit. Glad of that, too, because the urge to do too much to the image probably would have been strong, and I would’ve messed it up!
But I was looking at the settings, and remembered a topic that I wanted to discuss at some level of detail. I cover this because of all of the basics of photography, the relationship between the numbers was the most difficult for me to remember. Let’s start with a fundamental I’ve gone through before—the lighting in a photograph is a result of the interaction between the shutter speed (how long the sensor is exposed to the light), the aperture size (how big the hole is through which the light passes), and the ISO setting. The ISO setting is the more nebulous of the three, because it’s a measure of “sensitivity,” or what the sensor does with the light that hits it. I’m going to cover each of these three separately, starting with ISO.
Best way to think of ISO is the higher the number, the higher the light. Very simple—I mean, after all, that means “bigger is better,” right? Well, if you set ISO 400 you will get more sensitivity than you would if you had ISO 100 selected. But whether that’s “better” or not depends on what you’re after. For example, I shot this image pointing my camera more-or-less into the sunrise. The camera was set at ISO 100, fortunately, because anything higher might have resulted in “too much” light—leading to overexposed areas in the image.
If you’re shooting at night, on the other hand, there might be no such thing as “too much” light. The hole in your lens can only get so big (more on that in a later post in this series), and the longer you leave the shutter open the more risk that the image will be blurry. So in those cases, you want the sensor to do as much with the light as it can. This is accomplished by turning UP the ISO, going to a larger number. Remember—the higher the number, the higher the light. The compromise here is that a higher ISO number introduces an effect called “grain” or “noise” into the image, which can be unwanted in some (most?) cases. Fortunately, the modern digital SLRs are getting much better at managing noise, but some of the most common small-sensor cameras are not nearly as good. Finally, there are software solutions that can be used to remove noise, ranging from barely adequate to REALLY good. More to follow on that as the blog matures!
If you are setting the exposure of a shot manually by individually adjusting ISO, aperture and speed, you have to decide which is more important to you. In the case of ISO, you are thinking about overexposure if the number is too high in a bright scene, underexposure if it’s too low in a dark scene, and the tradeoff of noise at higher ISO settings.
Coming up: a similar bit of knowledge related to aperture and shutter speed…