Most lenses that are sold bundled with camera bodies are entry-level ‘kit’ lenses, and are likely to have an aperture range of f3.5 to f22 - especially if you have an APS-C or Micro Four Thirds sensor. Meaning that the widest aperture, and hence the shallowest depth of field, you can set is f3.5.
This usually works fine for head and shoulders portraits, as you are very close to your subject - but if you want a half body or full length portrait, then you have to stand further away from the subject, and so it is much harder to blur the background. This is why portrait photographers buy specialist lenses that have much wider apertures.
For example typical portrait lenses could start at f2.8 or even f1.8, and may also be 'prime' lenses, which means they are a fixed focal length and don't zoom. This means you can get an even shallower depth of field, and so it is easier to blur the background on portrait shots where you have to stand further away.
These lenses are sometimes referred to as ‘fast’ lenses, which is a bit of an odd term - but basically means that if you have a very wide aperture you can let in lots of light, which means you can shoot at faster shutter speeds.
If you are using a wide aperture lens, you will notice that when you shoot a head and shoulders portrait at the widest setting, you might focus on the eyes but find that the end of the nose and the ears are out of focus, as the ‘slice’ of focus is so narrow! Which means that using the widest possible aperture is not always the right answer.
The same applies for things like flowers or fungi, where you focus on the middle but the front and back edges are out of focus.
Another point to mention is that standard zoom lenses lose aperture at the wide end when you zoom in, due to the mechanical construction of the lens. So for example an 18-55mm kit lens for an APS-C sensor camera will have a possible aperture of f3.5 when zoomed out, but go down to a maximum of f5.6 by the time you are on full zoom.
There are some specialist lenses which don’t do this, and they are known as ‘constant aperture lenses’ but they are bigger, heavier and more expensive! These lenses are mainly used by wedding and event photographers, who need to create shallow depth of field at a distance, and also shoot successfully in low light.
Sensor size also affects depth of field - the larger your sensor, the more easily you can create shallow depth of field. So for example it is much easier to blur the background on a full length portrait when using a full frame camera (especially when paired with a wide aperture lens) than it is to do the same when using a camera with a smaller sensor.
If you are struggling to create blur in the background of a portrait, and you don’t have access to any other camera or lenses, one trick is to step back and then zoom in. You will lose aperture at the wide end as mentioned above, but you gain something called ‘telephoto compression’ which can enhance blur in the background.
The best way to learn is to experiment with different settings, crops and distances from the subject, to see what works best.
​
Return to the PTiYP app to continue.
For information on my 1-2-1 tuition services - which are available in person, or online via Zoom - please visit my photography tuition page.
I can help with anything from off-auto level tuition and learning how operate your specific camera, through to advanced skills, image editing and portfolio reviews.