Inside: New photographers often struggle to figure out what aperture to use.  This post gives you two questions to help you decide.  Read on to learn from my photography mistake!



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At six weeks old my third baby had begun to smile in earnest and I knew I HAD to capture it.

I settled the baby in her bouncer with a pretty blanket draped over the seat to create a nice background and enlisted my husband to help me coax out a baby smile.

My camera settings were ready and I felt my heart beat faster as my husband chatted with the baby in sing-song tones.

The moment came – her daddy’s voice made her face light up with the sweetest grin and I snapped away.

I reviewed my images on the back of my camera and saw a beautiful photo of my baby’s smile.

Success!  A keeper!

what aperture to use

…or so I thought.

Later when I downloaded my photos to my computer I admired my capture.

The exposure looked perfect and her grin made me giddy.

I imagined how much everyone would love this photo on her birth announcement.

I zoomed in…

what aperture should I use

Wait, the eyes.

My heart sank.

Her left eye looked blurry.

My excitement shifted to deep disappointment.

What happened? Where did I go wrong?

I had no idea.

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What Aperture To Use

As a new photographer I’d read the rule of thumb:

choose your aperture based on the number of subjects in your photo.

That was easy enough to remember.

So I’d chosen an aperture of f/1.8 because I had one person in my photo. Shouldn’t that have worked?  Why didn’t it work?  

How do you know what aperture to use?

The fact is


It’s true.  The aperture you should use depends on how many people or subjects are in your photo.

But other factors also need to be considered when you decide what aperture to use.

photography cheat sheet

Aperture, also known as f/stop, is one of the legs of the exposure triangle.  Aperture helps photographers create the beautiful, blurry backgrounds most people want when they are learning how to use their DSLR.

 what aperture to use

photo with blurry background taken at f/2.5

Lower f/stop = Shallow Depth of Field

A photo taken at a lower f/stop setting has a “shallow depth of field.”  A small “slice” of your image is in focus.

Think of it like a pane of glass running on a vertical plane through your image.  A lower f/stop setting will create a “thin” pane of glass through your subject.

This imaginary window pane, or in-focus “sliver” of the photo is called the “depth of field.” 

Remember, a photo taken at a lower f/stop setting, like f/2 has a “shallow depth of field.”  A photo taken at a higher f/stop, like f/11 has a “wide depth of field.’   


I Made One Simple Change


Scroll through the photos below and see if you can spot what I changed from the first to the second photo.

Hint: It wasn’t my aperture setting.

In the first photo notice only the toes are in focus.

In the second image notice how all of both feet and part of the legs are in focus, even though I didn’t change the aperture.

Do you know what changed from the first photo to the second?  Click on the photo to see a larger version:


In the example with my daughter’s photo taken at f/1.8 the shallow depth of field could not encompass both eyes.

How to Fix It

To fix the problem I could’ve closed down my aperture to f/2.8 or f/3.2 to capture both of her eyes in focus.


I could’ve taken the photo from further away to get both eyes in focus without adjusting my f/stop setting.

In the example above I took a few steps back but didn’t change my settings. 

I cropped in closer on the second image (in Lightroom) to show the increased depth of field created when I moved further from my subject.

But you can see here how far back I was compared to the first photo, which was not cropped.

I learned three important lessons from my photography mistake:

  • Mistakes are good!  I learn something important from every mistake I make.  I’ve learned to embrace them because they always teach me a lesson I’ll remember.
  • When I’m close to my subject a wider aperture won’t be the best choice because I want to get both eyes and most of the facial features in focus.  A higher f/stop number such as f/3.2 or f/4.0 may be a better choice.
  • Zoom in on the camera’s LCD to check focus!  If I’d zoomed in on those photos of my daughter I’d have realized I needed to adjust my aperture setting or back up a bit to get both eyes in focus.

How Do I Know What Aperture To Use?

The next time you need to decide what aperture to use ask yourself two questions:

1.  How many people are in my photo? 

Use one aperture stop for every person in the photo.  For 5 people, for example, use at least f/5.  And if they are on different planes, such as in rows, you may need to raise your f/stop number even more to get everyone in focus.

2.  How close am I to my subject(s)?

If you’re close to your subject for a portrait, use a higher f/stop to increase your depth of field and get all the important parts of the subject’s face in focus.

NOTE:  your lens and the type of camera you have also impact a photo’s depth of field.  Check out this helpful article to better understand how these other factors affect the depth of field in a photo.

Practice with different lenses if you have more than one. Different lenses will affect your depth of field based on their focal length.

If you’re new to photography I recommend a lens like THIS or THIS.  It’s a great lens for beginners!

Learn From My Mistake

Learn from my photography mistake and take your distance from your subject into account when you choose what aperture to use.  You’ll avoid download disappointment and increase your keepers.


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