What is a cameras aperture?

With DSLR (digital single-lens reflex) cameras you can change your lenses as most people know.  What many people don’t know is why some lenses give a blurry background and some will only take photos where mostly everything is in focus.  The reason for this is the lens aperture.

Your aperture is one part of three that determines how much light your camera lets into the sensor.  Your shutter speed and ISO are the other two factors.  To keep it simple I will just reference the lens used in the photos below.  I use a Sigma 35mm Art 1.4mm which is a prime lens.  Prime lenses do not have the capability of zooming in and out.  The 1.4 means that my lens has a minimum aperture of 1.4mm which is very wide open aperture and allows a lot of light in.  My lens has a maximum aperture of 16mm which will keep a large group in focus.

So what is aperture really? Aperture is the light your camera allows to enter and be read by the sensor.  The lens controls this by making the tunnel (lens) wider or more narrow.  The wider the lens is open the brighter the photo will be and the more blur (we call this bokeh) will be around the subject and the more the subject will stand out.  The more closed the lens is the less light it lets in and the more in focus everything will be.  Neither style is better, it is just a matter of personal preference.  I choose the style based on the environment I’m taking photos in.  In these photos of Fred you will see how each photo becomes more in focus.

So what changed to make Fred more in focus?  No I didn’t change my aperture, it is at 1.4 in every photo.  The difference is the distance I was standing from him.  In the first photo I could have raised the aperture up to a higher level and he would be more in focus such as this photo below which was taken at 4.5 mm.

Unfortunately this does get more complicated.  If you want to take a group photo with 5 people, 10 people, 20 people, and 40 people. You could say that you need a higher aperture due to the number of people, but that isn’t necessarily true.  As you saw in the first example with Fred, you can use one aperture setting and the further you get back the more in focus the subject becomes.  You’ll notice a line of focus when you use a shallow depth of field.  If all the 5, 10, 20, or 40 people are in a straight line shoulder to shoulder they will be in focus the same as if it was one subject.  If the people turn sideways the line will fall on the same level as your focus.  If you focus on an eye their front and back arms/shoulders may not be in focus but their faces would be.  If you stagger the people so there are some in the front and some in the back, the person you focus on will be the line and everything else will be out of focus if you use a lower aperture.  In this instance you would need to increase your aperture.  The more levels you add the higher your aperture needs to be.

Think of a bowling pin type setup

            –                                    You (photographer)

      –                                    Row one=1.4 mm
–   –                                  Row two=7.1 mm
–   –   –                                Row three=9 mm
–   –   –   –                             Row four=11 mm
–   –   –   –   –                            Row five=16 mm

This isn’t completely accurate because it is situational but hopefully it makes some sense.

If you pay attention in this photo of Fred, you will see his left eye is completely in focus, his right eye is slightly less in focus, his nose and mouth are barely in focus, and everything from his ears back is blurry.  This is what happens with a shallow depth of field up close.  His left eye is in focus because that is where I set my focus point.  If you are taking a portrait and want to use a lower aperture to get the blurry background you must step back further from the subject.

How does this information apply to those without a DSLR?

Most smart phones have a pro setting where you can change your aperture!  Of course it won’t give the same results, but now when you look at that setting you’ll at least have a general understanding of what it means.

I have a Samsung Galaxy S8.  Here are a few photos I took to show you the pro mode on manual adjusting only the MF (manual focus aka Aperture).

This is my menu for different shooting modes I can use.  I selected the Pro mode.

As you can see here I have selected MF and you can see where there is the flower on one end and the mountain on the other end.  The closer you get to the flower the lower the aperture you are using and also the closer you will need to be to the subject, the closer to the mountain the higher the aperture.  The aperture on the phone does not work exactly the same as a DSLR.

Here is an example of a photo taken with a lower aperture (don’t mind my dusty keys, focus on the pretty colors instead!).

The best way to learn is to work at it.  Go pick up your camera and go to manual mode and just keep adjusting the aperture so you can see what your specific lens is capable of.




I am Amy Sine, owner of Amy Sine Photography LLC in the Morgantown, WV area.  I specialize in Newborn and First Year photography.  I have been published by Inspire Magazine, Newborn Magazine, Photography magazine, and featured in an SLR Lounge article.  I was nominated as a top newborn photographer by Beauty and Lifestyle Mommy Magazine as well as awarded an excellence award by Photography Magazine for my image titled “Coal Miner’s Daughter.”

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