Sunday, October 25, 2015

Understanding Depth of Field and Focus

Focus is EVERYTHING when you want to take a beautiful photo.
I am going to try to teach you how to focus using
FOCUS POINTS on your DSLR camera plus
explain DEPTH-OF-FIELD and how it is controlled with aperture.
I know it sounds scary, so I'm not going to include lots of
confusing math....just the very basics that you will need to
 FINALLY get the correct focus all the time!
This tutorial is only for DSLR cameras because they allow
you to take control of your focus.
Let's start with that comfortable AUTOMATIC mode you are probably
using, and wondering why your subject's face isn't in focus all the time.
I shot this in AUTOMATIC:
In Automatic, you allow your camera to select where to focus.
This did a pretty good job.  You would probably post this on Facebook,
 but lets go in closer and see that...
her eyes are not sharp:
Now, let's zoom in on the bowl of gourds she is holding...
This is where the automatic mode chose to focus.
Time to go into the manual modes and take control of focus.
To make it easy...we'll go semi-automatic and use the AV mode or Aperture Priority
mode on a Canon.  "A" mode on a Nikon.
Read your camera manual to learn how to set this on your specific camera.
In this mode, you get to choose your aperture and the camera will automatically set the
shutter speed to give you a good exposure.
If you find that your camera is setting your shutter speed below 1/125, (In a darker situation.)
you will need to raise your ISO until you get at least a 1/ 125 shutter speed to avoid
hand shake blur.
Next, read your manual and learn how to use FOCUS POINTS.
This takes practice to learn how to use them, but it will
change your photography forever.  You will no longer have
blurry eyes! 
DSLR cameras have a grid of focus points that you can move around
and place one directly over an eye or whatever you want in tack sharp focus.
In this next photo, I want to focus on the fried eggs, so I set my red dot
focus point directly on the eggs.
By using focus points, you will finally be able to create those
artistic photos where the exact item like these fried eggs is in perfect focus
while the surroundings are blurred.
Once you learn how to use focus points, you are
ready to understand depth-of-field and how to
control it with aperture.
Depth-of-field is the distance between the nearest and farthest
object in a photo that appears acceptably sharp.
When photographing a person, you should set your focus point
on the eye closest to the camera...unless you're creating some kind of artistic
statement and want to focus on the tip of the nose.
So let's say your focus point is on the closest eye.
That focus point on the eye becomes the center of your
depth-of-field and will be in tack sharp focus.
By showing the side view, we can see this
depth in front and in back of the focus point.
With this depth-of-field, we can see that her entire face and hat will
be in focus, but the front of the bowl of gourds and her mittens will blur.
Aperture determines how much in front and in back of your
focus point will be in focus.
Aperture is how much your lens opens up to let in light.
The BIG hole is a big aperture, but to make it very confusing...the
lower the aperture number the bigger the hole/aperture!
So, an f 1.4 is a BIG hole/aperture
and an f  22 is a SMALL hole/aperture
I know...totally confusing...but once you wrap your brain around it,
it becomes second nature.
REMEMBER THIS:  The bigger the aperture the smaller the depth-of-field!
So, it makes sense that if we want the eyes in focus, but lots of pretty
artistic blur, we will want a bigger aperture.
Let's start with a BIG aperture with the small number... f 1.4.
This is the biggest aperture on my 50mm lens.
Since the bigger the aperture, the narrower the depth-of-field,
you can see in this next photo that when you set your focus point
on the eye....not much else is in focus.   Even the tip of the nose is not in
focus!  Most of the hat is not in focus, her ears are out of focus.
If my subject is facing me square on with both eyes on the same plane,
the f 1.4 will create a lovely photo with both eyes in focus.
It's okay to have facial features out of focus as long as your eyes ARE in focus.
But, if her face is angled even a tad...
the eye furthest from the camera leaves the narrow depth-of-field
and is no longer in focus!
Notice the gorgeous bokeh (artistic blur) in the background!
This is why portrait photographers want to use the biggest
aperture possible and still get those eyes in focus.
But the f 1.4 is too narrow to get the angled back eye in focus.
You need to be very aware of aperture and depth-of-field while shooting
in bigger apertures.
Let's keep her angled face and close down the aperture a bit to f 2.8
creating a tad larger depth-of-field to include the eye that's a bit farther back.
Let's go in closer to see that both her eyes are in focus,
but the aperture is still big enough to create the gorgeous bokeh in the background. 
Let's close down the aperture to f 5.6 and see that more is in focus,
plus the bokeh is  smaller. (But still pretty.)  
YOU get to choose
the look you want in your photo and YOU get to create it by choosing
the aperture and thus your depth-of-field!
A quick summary:
Select your aperture based on what you want in focus
Smaller number aperture means wider open hole in lens.
Larger hole in lens means narrower depth-of-field and less in focus.
Focus on the eye closest to the camera!
You may have to read this over and over...but once it clicks in your mind...
you'll be clicking your camera like crazy
and nailing focus EVERY TIME! 


  1. This is a wonderful guide to newbies, like myself.
    Now the biggest debate I see on forums for people like myself is with the Canon model style lenses... is the Canon EF 50mm f/1.8 ll Lens more useful for portrait photography than the Canon EF 40mm f/2.8 STM lens?
    I'm still learning the ropes and the new lingo, but an answer to this question would be much appreciated. Also, thanks for make such easy to understand guides for us blonds, haha!

  2. Hi Kylla, Thanks for your kind comments! I have never tried the Canon EF 40mm f2.8 lens. My favorite and go-to portrait lens is the nifty fifty mm 1.4 lens! I like to be up close to interact...especially with children. The 85mm is better with compression and background bokeh...but I don't like having to be far away while shooting. It's all what works best for the photographer and what they are trying to accomplish.

  3. Thanks for such a speedy response!
    Now question again, if you prefer that, does that mean your portrait shots are always going to be "one eye of the subject out of focus because such a narrow range"? I might be reading the article wrong, but doesn't that just have a small "window" for focus ability?

  4. Kylla, I was referring to the lens I love which is the Canon 50mm 1.4. This does not mean I always use the biggest aperture for portraits. This is explained in the blog post. You use the aperture to create the focus that you want. Hope this clarifies.