Eric Stewart: Running Off At The Mouth

When you’re using a dSLR, and you’re using any of the modes that don’t calculate things for you automagically, taking a good photo can become quite tricky.  A couple of key concepts take a bit to nail down, and will probably require some trial and error almost every time I go to take photos:

1. The amount of light that actually hits the sensor: Aside from the light sources available to you, so far I’ve learned about three key settings that impact this:
   1. ISO speed: this determines how sensitive to light the sensor itself is.  The problems that occur are that high ISO/sensitivity values can lead to photos that introduce “noise”.
   2. Shutter speed: this is a measure (the fraction of a second, usually, though really creative photographers might use multisecond shutter speeds for some photos) that the shutter is opened to allow light in.  In general, the higher the ISO speed (and Aperture value, explained below), the faster the Shutter speed.
   3. Aperture value: This is a measure of how far the aperture/shutter opens during the shot.  It’s value is also known as an “F-stop” and is actually an inverse measure; F11 means the aperture opens smaller than when it’s set to F2.8.  Lenses can have a minimum (or actually, maximum) value, but the camera can be told to have a smaller aperture opening.
2. Depth of Field: This can be a key factor, particularly when you take close up or macro shots.  While not a “measure” in and of itself, it’s the range from the lens where items in the picture will be in focus.  A narrow DoF will have only your main subject (and maybe even only part of your main subject) in focus.  A wide DoF will have your subject and possibly things in front of and behind your subject in focus.  So far, I’ve learned about two things that have a lot to do with DoF:
   1. Distance from the lens:  The farther away something is from the camera, the wider the DoF.
   2. Aperture value: smaller aperture openings apparently provide a wider DoF, whereas larger openings provide a very narrow DoF.

So when you stop to think about it, it can be quite tricky to balance it all out.  If you’ve got a fast moving subject (or even just a subject that might move noticably while the shutter is open), you’ll want to have a high shutter speed to avoid too much motion blur.  But you also want to have a smaller aperture to give you a wider depth of field, and you also want to have a lower ISO to avoid noise in the photo.  But unless there isn’t a cloud in the sky, you’re likely to have to compromise somewhere.  Indoor photos, even with a flash, can result in a tricky balancing act between F-stop, ISO, and Shutter speed.

And I doubt I’m done learning yet … 😉

The day’s pictures that were worth posting are on my ericdives.com gallery.