Depth Of Field: Changing Focus Points – Photography Experiments

Changing Aperture - no just for bovines any moreChanging Focus Points

Let’s try a little Jedi training with you today. I’m not going to give you any supporting images to help you see what might happen.

“LUKE: (laughing) With the blast shield down, I can’t even see. How am I supposed to fight?

BEN: Your eyes can deceive you. Don’t trust them.”

Actually, Old Ben had it wrong, I want you to trust your eyes.

Oh, this is post 4 in the 40 Photography Experiments.

Now then, yesterday you learned to change the depth of field in a shot using the Aperture. Today let’s see what happens when you change the focus point in a scene.

Here’s the experiment you can run:

1) Scene setup: You will need a long, flat surface, like a wall or a floor. A table or counter will work as well.

2) Place a yard stick along the table or wall. Yeah, I know, the chances of actually owning a yardstick are slim. So set up an object every foot along the table for a total of six feet. Taper them side to side slightly so you can see them all at once, much like you did yesterday.

3) Switch your camera to Aperture Priority. Choose ISO 800 and pick the smallest numbered aperture you can (e.g. f/4, f/1.8).

4) Switch your camera to select only the middle focus point. There are dozens of ways to accomplish this depending on your camera so I suggest you consult your manual to learn how to pick just one focus point and keep control of it. If you really can’t find it after reading for 15 minutes, leave a comment and I’ll help you.

5) Zoom in to 50mm or as close as you can get to that focal length. If you are using a point and shoot, zoom in half way from the nearest to the farthest zooms.

6) Focus on the first object and get as close as you can before your camera won’t focus any more. This will be somewhere around 1-2’/.3-.6m.

7) Make sure you can see all the objects on the table/floor/counter. You can use a wall that has some type of pattern on it. If you have no patterns, give your kids some crayons and tell them to go to town on the wall. Instant, random patterns.

Get ready, get set…

Let’s just review where you’re at as we’re doing this without photo aids.

Stuff spaced out at one foot/.3m increments on a table/counter/floor or some type of pattern on a wall. You have control of your Aperture and ISO and you will let your camera take control of Shutter Speed.

You selected the smallest numbered aperture you can, likely f/3.5 or f/4, but maybe less. It’s not too important right now. Oh yeah, make sure there is decent lighting. And chocolate. It’ll help, trust me.

8) Take a photo while focused on that first object.

9) Focus on the second object. Do not move your camera front to back or too far left and right. Panning to the side (as if your camera is on a swivel) is best. Baby steps.

10) Take a photo.

11) Focus on object #3 as above and take a photo.

12) Continue this until you have shot all objects in turn.

Done! With the shooting.

Now review the images on your computer. Run through them one by one and look to see how many objects are in focus in each picture.

Remember, you changed nothing in between the photos as far as your camera goes except the point of focus (shutter speed changes in this experiment are irrelevant). So how many objects were in focus when you focused on the first object and how many were in focus on #4?

What happens if you run the experiment again and choose f/8 or f/22?

I’m not going to give the answer to this one today, maybe on Monday. I’m waiting for you to have your “LUKE: You know, I did feel something. I could almost see the remote,” moment.

What? Too many Star Wars references?

Monday we will build on the Depth Of Field concept by changing distance and zoom.


Questions?  Pop ’em like Pez in the comments section below. or email me at peter@peterwestcarey.com.

Photography Basics – A 43 Day Adventure, and its companion 40 Photography Experiments, are series written by professional photographer Peter West Carey. The series are designed to unravel the mysteries of photography, helping you can take better pictures. Subscribe here to receive all the updates and bonus material. Your comments are always welcome.

Photo ToursIf you enjoy the series, consider learning photography first-hand on a professionally led international photo tour in Nepal or Bhutan. More information can be found at Far Horizon Photo Tours

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