The Great Photography Aperture Lie
I hate to tell you this, but you’ve been lied to about aperture!
Hi, my name is Rich Dyson from Edinburgh Photography Workshop, and this is Coffee Break Photography.
Last week, I discussed the basics of exposure. We looked at ISO, shutter speed, and aperture and their effects on photos. In that video, I also told one of the biggest lies that new photographers are taught. If you remember, I showed how a large aperture (that’s a low f-number) led to a shallow or small depth of field and vice versa. A small aperture (with a large f-number) gives us a large or wide depth of field.
The fact that I could show two photos proving this happens seems to confirm that the depth of field of a photograph is influenced by the camera’s aperture. Most of the time, we are only taught the partial truth about depth of field.
Let’s look at a setup similar to that used during my Switch to Manual sessions. I’m going to shoot this street sign with an aperture of f/3.5. The zoom is at the widest angle, which is 24mm on this lens, and I stand about thirty centimetres from the first letter on the street sign, which is where I am focusing. You can see that the first letter is acceptably sharp, and the sign blurs the further away it is from the focus point.
I’ll prove again that changing the aperture to f/14 affects the field depth. The first letter is still sharp, but the acceptably sharp area has extended further along the sign.
We can see the maths of what I’ve just done on one of my favourite photography apps, Photopills. You type in the focal distance, aperture, and the distance to the subject, and the app displays a visual representation of the depth of field. When the aperture was f/3.5, the depth of field was calculated as three centimetres. Change it to f/14, and the depth of field extends to thirteen centimetres.
Now, let’s start showing where things begin to go astray. Instead of standing thirty centimetres from the first letter on the sign, I will move back a couple of steps to stand one metre away. The aperture has stayed at f/14, but if we look at the picture, the acceptably sharp area has extended even further. Let’s put this into the app, and you can see the depth of field has been calculated to three metres and seven centimetres.
So, in addition to being influenced by the aperture, the depth of field is also influenced by the distance from the subject. The closer we are to the subject, the shallower the depth of field. Conversely, the further from the subject, the greater the depth of field.
That isn’t the only influence. This time I will stay standing a metre away from the subject and still use an f/14 aperture. However, instead of keeping the zoom at twenty-four millimetres, I will zoom in to seventy millimetres. Let’s look at the photo before we see how the app reacts. The depth of field has almost returned to the area covered in the second shot. Now let’s look at this in the app, and you can see that by zooming in, the depth of field has reduced again, this time back to sixteen centimetres.
In addition to aperture and distance, the depth of field is also influenced by the zoom used. The wider the focal distance, the wider the depth of field. As we zoom in on the lens, the depth of field is narrower.
With this knowledge, I’ll show you how big the lie of depth of field is. I’m in Leith, shooting across the water from the newly re-opened Victoria Swing Bridge. The distance from here to the road is twenty-six metres. I’ve changed the zoom back to twenty-four millimetres and set the aperture to f/2.8.
According to what we usually think about depth of field, you might think that the image should be blurry. But here’s the shot and everything is acceptably sharp. Despite using an f/2.8 aperture, the depth of field is infinite—well, almost. You can see on the Photopills app that anything from my camera to 14.93 metres would be outside the depth of field, but then everything from there to infinity will be acceptably sharp.
I can highly recommend the Photopills app. It’s got some other great features, but trying out different focal distance, aperture, and zoom combinations is really going to help improve your photography.
If you’ve enjoyed this video, it would be great if you could like it and share it by clicking on the thumbs-up button below the video. That way, a few more people will get to see it. You can also subscribe to the channel by clicking on this button here. I send out a monthly newsletter to my subscribers with news about photography and exclusive offers. Scan this QR code to sign up. My name is Rich Dyson, from Edinburgh Photography Workshop, and this has been Coffee Break Photography. See you next time.
