Understanding Focal Plane & Depth of Field

Understanding Focal Plane & Depth of Field

If you are anything like me, when you're reading about photography related topics and the big words, then the weird numbers start flying at you… it takes about three sentences and you give up! 

I am going to explain focal plane & depth of field in a very simple and understandable way.

I will show you how you can use a low f-stop even when shooting multiple subjects, and how to keep them all in focus!

What is Depth of Field?

A basic definition of depth of field is the area of sharpness within a photo that will appear in focus.  I hear every single day someone say that they are scared to use a low f-stop. Stop the madness!!  F-stops 1.4, 1.6, 1.8 can all be your friend, I promise!

First and most importantly, if you want to shoot at a low f stop you are going to have to learn and understand the term “focal plane”. 

What is Focal Plane?

The definition of focal plane is the distance from the camera at which the sharpest focus is attained.  I think of it as an imaginary line that runs from right to left across your photo.  Picture yourself in a field with a nice set of trees far off in the background and your family right in the center of the field. 

If you took a piece of tape and stretched it straight across the field left to right and made your family stand on the tape, if its one family member or 10 members… they will all be in focus, even at f1.4.  Now, if one of them steps in front of, or behind the tape, they will be out of focus… because they stepped out of the “focal plane” (i.e. your piece of imaginary tape).

At f1.4 your tape is very thin, think of a roll of scotch tape.  The higher you take your f-stop the thicker your tape gets… eventually turning into a wide roll of packing tape.

You also need to be aware of where you are in relation to the subjects.  When using a low f-stop you need to remain directly in front of your subjects… you can’t wonder off 8 feet to the left.  You need to be centered and head on to your subject.  The tape line is only as straight as you are… if you wander off and get crooked, so does your tape.

How to Shoot Wide Open and Get Multiple Subjects in Focus

I am going to use this series of photos to help explain how this is done.  I am going to shoot at 1.4 for all of these “poses” below, and explain why it works!

Ok, let's do this!  So our first photos here is a nice little Buzz and Jessie family with three baby aliens and a pooch.  I focused on momma Jessie’s face in every photo, with my f-stop at 1.4.  Why are they all in focus even though Buzz and Jessie are tall and the babies and dog are short?

Because they are all on the same “plane” tall to short is of no matter!  It is all about if they step in front of, or behind your piece of imaginary tape (aka the focal plane).

Now, lets say that evil Uncle Zurg shows up to the photos shoot with his evil Buzz clone and pet dinosaur… and Jessie decides to ask you for an extended family shoot!  You really don’t want to, but also don’t want to anger evil Uncle Zurg.

It’s getting late and dark so you need to use a low f-stop… it’s fine really!!  Back to your focal plane… or piece of tape.  Just get them all on that piece of tape and you will be fine… 1 or 10 evil extra family members won’t make a difference. 

Now, it's kind of hard to get plastic people to hold hands, look longingly into one another eyes, or horse laugh, so these poses look a bit stiff, but your subjects can move, lean on, or look at on another and still be in focus.  They don’t need to stiffly stand shoulder to shoulder. 

Say you want to separate the evil from the good members into groups for your shot.  That can also be done!  The subjects don’t have to be standing side by side.  You can have one group on the right and left, or three groups all separated, or any type of grouping you choose.

Just be sure they are on the same focal plane, and only two people deep in the stack… i.e. no more than tow rows of people.  If you choose to “stack” people two deep, you will need to raise your fstop just a bit to “thicken” your “tape” for two rows of people. 

I shot this photo below at 1.8.

Now lets say you want to get one of those shots where the family is bundled up together looking at one another laughing… This can also be done at a low f-stop, I promise!!

It’s extremely simple… just back up.  Really, thats it… just take a few steps back.  How far?  I really don’t know, it depends on several things, the lens your using, the amount of people in your “stack”.  A few feet, a hop skip and a jump, two hairs past a freckle, some.  I am not technical and I don’t really measure well.

The best way I can describe how far is to say that momma Jessie’s whole head should be able to fit inside your little focus window in the view finder on your camera.  If its just an eye or face inside your little square then you are too close.

Yes, there are mathematical, technical ways to find out how far, but I don’t understand them :).  Just take a test photo, zoom into your viewfinder and check your focus.  If someone is out of focus… take another step back and try again.

More Focal Plane Test Photo Examples:

I took this shot close up, so to get all the subject is focus I had to up my f-stop to 4.0.

I took this photo too close at 1.4, so the only subjects in focus are Buzz and Jessy (This is what you don’t want).

I backed up several feet and tried again at 1.4 and bam… everyone in focus!

How to Get a Nice Blurry Bokeh Background

Another important thing to remember when you want to create a nice blur to your background (this is called shallow depth of field), is to move away from the background as far as you can… create some space between your subject and the trees.

Now, I am not suggesting that you go take your next paying client out, and stick your camera on 1.4 and let it fly.  What I am saying is that IT IS POSSIBLE to use a low f-stop when you are wanting a nice blur or bokeh to your background, or fighting a low light situation.

Now its your turn!  Take a friend out and practice, get comfortable with a low f-stop so you can use it when you want to, or when you need to!

Do you have any questions or comments about Understanding Focal Plane?  Leave me a comment below - I would love to hear from you!  And PLEASE SHARE this post using the social sharing buttons (we really appreciate it)!