Lesson 51: The Rule of Focus

In yesterday’s lesson, we talked about holding still.  The reason holding still is important is because of the Rule of Focus.  The Rule of Focus was once stated to me by a photography instructor as:  “If at least one thing isn’t sharp, your image will fail.”

If you’ve been following along since the beginning, you may recall that in Lesson 4, I talked about a photograph where nothing was sharp, yet it is considered by many to be among the most iconic rock and roll photos ever taken.  So, just like all other “rules,” this too can be broken.

That said, most of the time, it’s true that blurry photos don’t work.  In fact, getting sharp pictures is what drives many photographers to spend thousands of dollars on expensive lenses to get the sharpest image possible.

There are multiple parts to achieving focus.  We talked about motion blur caused by a moving camera in yesterday’s lesson.  We also talked about motion blur caused by a moving subject in Lessons 31 and 32.  Today, we’re going to talk about Depth of Field.  Now, I alluded to depth of field in Lesson 30 when we explored using a Hipstamatic lens that puts only a small portion of the photo in focus.  We also talked about depth of field in Lesson 41 when we talked about putting a human subject far from the background to increase background blur.

Today, let’s talk about some of the benefits of depth of field we get automatically when we shoot with an iPhone.  The easiest way to think of depth of field is to think of the scene you’re shooting.  The scene is 3 dimensional even though your photo has only 2 dimensions.  If you were to lay a ruler on the ground from the front of what you can see to the back of what you can see, the distance that remains in focus in your photo is called depth of field.

The point where sharpness begins is usually a bit in front of where you focused.  The point where sharpness ends is usually about ⅔ of the scene back from the point where you focused.  With the iPhone, the depth of field is far greater than with a DSLR camera with comparable settings because the sensor is so small.  This is a weirdness about depth of field–how small the sensor is affects depth of field in ways that are surprising if you don’t go into detailed, technical explanations about how light works to create images.  And, I promise, I won’t.

Here are the things that are important to remember:

  1. If you’re shooting a landscape, you generally want the photo to be sharp all the way from the front to the back.  To achieve this, try to keep objects closer than 10 feet out of the frame.  Then, select the closest object in the frame for focus.  The background will usually remain reasonably sharp.
  2. If you’re shooting a person, you generally want the person to be really sharp, especially the eyes, and you don’t care about the background–in fact, it would be better if the background were out of focus.  Focus on the person’s face or let the camera use facial recognition to achieve focus.
  3. If you’re shooting something up close, like the flowers I used in yesterday’s lesson, remember that you have to be a certain distance away to get sharp focus.  You might notice that the petals in the following photo that are closest to the camera are not sharply focused.  That’s because they were too close.  By backing away, you can get the entire bouquet in focus when you select the closest petals.

Your Assignment:  Choose a subject you’d like to have completely sharp.  Move closer and further away to determine how close you can get before the foremost part of the subject remains blurry.  Experiment with selecting different focus points to see the best place to choose focus to get the entire subject in focus.  Also try taking pictures of your favorite person to see if you can get their face sharp.  Don’t forget about the Rule of Holding Still.  If you have a landscape you can shoot, see what happens when you tilt the phone so the closest object is at least 10 feet away and you focus on that.  Try it again focusing far back in the scene and again focusing very close.  Which images have the most depth of field?  Which ones do you like best?

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