Tip of the Day - ISO

I'm sure you've noticed that in the last two tips there has been a trade off-- different benefits or effects depending on which way you take the element under discussion. In terms of aperture, a wide f-number yields one effect, isolating the subject against a blurred background, and a narrow f-number yields another, a deep range of focus to have all or many of the elements in focus. With shutter speed a photographer trades action stopping power for the ability to capture picture in low light.

The range of options available when talking about ISO (or film/sensor sensitivity to light) represents a similar type of trade off. A lower ISO number-- say 64 or 100-- represents the lowest sensitivity to light, but give the highest image quality in terms of graininess or "noise." Higher ISO numbers allow you to capture images in lower light settings, but add "noise" to the image, making them less and less suitable for enlargements.

Here are some examples to illustrate this point:


This image was take in full sun at the lowest ISO setting on the camera--100. The close up shows that the dark areas are nearly perfectly uniform.



This image, however, was taken at dusk and from some distance away. To allow shutter speeds that could remotely allow me to hand hold the camera, I bumped the ISO setting to the highest on this camera--1600. Notice the significant graininess or noise--especially in the darker areas.

If you don't plan to enlarge your images much beyond 5x7 then the higher ISO settings aren't too much trouble. The noise is not as noticable in smaller prints. At 8x10 or above, however, you should try to capture your images with the lowest ISO setting you can get away with.

Newer cameras manage image noise at the higher ISO settings much better. The newest Nikon professional grade DSLR, the D3, shows exceptional image quality, even at ISO 3200. See below:


The D3 can also go three full stops beyond 3200 to an astonishing 25600.


The ultimate take-home lesson from the tips on aperture, shutter speed, and ISO is to manage your ISO like you manage your shutter speed and aperture. Keep in mind the effect you are working for and adjust accordingly. If enlarging your images is important--keep your ISO low and open your lens wider or use a slower shutter speed. If capturing action is paramount--use higher shutter speeds, even if bumping your ISO up a little is necessary. To isolate that head shot against a blurred background, open your lens to its wider apertures.

So... how are your photographs improving? Post a comment here and let me know how you're doing and if you have any questions.

Tip of the Day - Aperture, part 1

I taught a photography mini class not too long ago and I realized in talking to those students that not everyone knows the three basic physical elements that determine the exposure of a photograph: aperture, shutter speed, and ISO. A basic understanding of these three things gives a photographer much more control over what kinds of picture he/she will achieve.

Basically, aperture (also called f-stop) is the size of the hole that lets light through the lens (similar to the pupil of your eye). Shutter speed is how long the shutter is open to let light through that hole. ISO is another term for film speed, which is a measure of a film's (or digital camera's sensor's) sensitivity to light. These three elements combine in many different ways to achieve different results.

Before we discuss how aperture creates story, let's look at how the three elements work together. To achieve a properly exposed photograph (saying nothing, for the moment, about composition or color or anything else) the camera must receive the "right" amount of light on the film or the sensor. Let's call that amount X. Amount X is roughly the same for each ISO setting or film speed. X is equal to 100 for 100 speed film or an ISO setting of 100 on a digital camera (there is some complicated math behind this, if you are interested). Depending upon how much ambient light is available in the scene you are photographing, the photographer (or the camera) adjusts the aperture and shutter speed to get the needed amount of light to the sensor or film.

A large aperture means that lots of light gets through the lens to the sensor at a time. A small aperture means less light gets through at a time. If lots of light gets through quickly, then the shutter does not have to stay open as long. If little light gets through, then a longer shutter speed is needed. Additionally, a sensitive sensor or film means that less light is necessary to achieve the correct exposure. Kind of basic stuff, but, as I said, not understood by some photographers and therefore worth reviewing.

I'll discuss shutter speed and ISO in more detail another day. Today I'm posting about the ways that aperture creates effects on the image you get (or the image you are trying to get). Take a look at part 2 of this tip, which is posted separately.