Subject Isolation and Bokeh
Portrait photographers are obsessed with subject isolation and bokeh and the many different ways to achieve smoother, less distracting backgrounds. Most well-versed photographers would know that the aperture of a lens affects the out of focus areas. Use a larger aperture, such as f/1.8 or f/1.4 and the backgrounds will be lush and smooth. In fact, most non-portrait photographers will probably already be very impressed with the bokeh they get at f/2.8.
But it's not that simple, whilst using a larger aperture allows for smoother, more out of focus backgrounds, it doesn't necessarily help with subject isolation to the degree most people would think it does. Let's take a look at three examples, shot with the following settings. I won't tell you which one is which, but of course, try to take a guess!
But it's not that simple, whilst using a larger aperture allows for smoother, more out of focus backgrounds, it doesn't necessarily help with subject isolation to the degree most people would think it does. Let's take a look at three examples, shot with the following settings. I won't tell you which one is which, but of course, try to take a guess!
- D750 + Sigma 50mm f/1.4 ART at f/1.4
- D750 + Nikon 85mm f/1.8G at f/1.8
- D750 + Nikon 70-200mm f/4 VR at 200mm f/4
The first image is the 70-200mm, the second is the 50mm and the third is the 85mm. We could tell this from compression, i.e. the ratio of the size of the foreground elements to the background elements. Here, it's quite clear that with the 50mm lens, we could see the most background, in that the background is less blown out. At 85mm, we're quite blown out and by 200mm, we're completely blown out, the background is so huge that we can't quite distinguish what it is anymore.
Of these three images, the 85mm f/1.8 definitely exhibits the smoothest bokeh (out of focus areas). This is, somewhat, to be expected. Even though the 50mm lens was shot at f/1.4, the slight increase in aperture makes less of a difference compared to the substantial increase in focal length. Note that both the 50mm and 85mm lenses produce very smooth out of focus areas, but the effect is very different. With the 50mm, we have a much greater sense of placement and space, whereas with the 85mm, we see much less of the environment.
This leads me to the first point, that subject isolation isn't all about depth of field. With shorter lenses, such as 50mm, you have to use extremely large apertures in order to create lush backgrounds. When you increase your aperture, you simply shorten your depth of field, meaning that you make less and less things in focus. The counter-effect of this, of course, is that the lines between your subject and your background also become blurred. This gives images the creamy, smudged look, which is nice, but is definitely overdone. Take a look at the second image and look at where the subject blends into the background, the gradations are very smooth and lush, not hard. This gives an impression of blending in, rather than of stark separation.
With the 85mm f/1.8G, since we use a slightly smaller aperture, we see this effect to a lesser degree. The backgrounds are more lush, but the gradations between foreground and background are much more pronounced. Physicists call this specular highlights - they're much more prominent on the 85mm f/1.8G compared to the 50mm f/1.4 ART. Whilst most people get their first dip into bokeh with these lenses, portrait pros are all out on the field with huge 200mm f/2, 300mm f/2.8 and 400mm f/2.8 lenses. Why are they so obsessed with length? Take a look at this image.
Of these three images, the 85mm f/1.8 definitely exhibits the smoothest bokeh (out of focus areas). This is, somewhat, to be expected. Even though the 50mm lens was shot at f/1.4, the slight increase in aperture makes less of a difference compared to the substantial increase in focal length. Note that both the 50mm and 85mm lenses produce very smooth out of focus areas, but the effect is very different. With the 50mm, we have a much greater sense of placement and space, whereas with the 85mm, we see much less of the environment.
This leads me to the first point, that subject isolation isn't all about depth of field. With shorter lenses, such as 50mm, you have to use extremely large apertures in order to create lush backgrounds. When you increase your aperture, you simply shorten your depth of field, meaning that you make less and less things in focus. The counter-effect of this, of course, is that the lines between your subject and your background also become blurred. This gives images the creamy, smudged look, which is nice, but is definitely overdone. Take a look at the second image and look at where the subject blends into the background, the gradations are very smooth and lush, not hard. This gives an impression of blending in, rather than of stark separation.
With the 85mm f/1.8G, since we use a slightly smaller aperture, we see this effect to a lesser degree. The backgrounds are more lush, but the gradations between foreground and background are much more pronounced. Physicists call this specular highlights - they're much more prominent on the 85mm f/1.8G compared to the 50mm f/1.4 ART. Whilst most people get their first dip into bokeh with these lenses, portrait pros are all out on the field with huge 200mm f/2, 300mm f/2.8 and 400mm f/2.8 lenses. Why are they so obsessed with length? Take a look at this image.
This image was taken at 200mm f/22. That's right, not f/2, but f/22. Yet, the backgrounds look more than acceptable. It actually looks less distracting than the 50mm f/1.4 ART and the transition between subject and background is very, very pronounced. Of course, we're diffraction limited here, but if shot at f/8 or f/11, we'd get extremely sharp foregrounds.
Longer telephoto lenses have compression properties, they make people look more flattering because you're standing further away. That's a topic for another article, but they also have the very unique property of being able to separate the subject and background very decisively because they make the background so large and blown up. On top of that, unlike with shorter lenses where you have to use large apertures to give yourself that separation, telephoto lenses can do it with much larger apertures. Take a look at that shot above at f/22, look at how sharp and in focus the subject is and look at how that background is completely undistracting.
The takeaway point from all of this is that for bokeh and depth of field, it's all about the aperture, but bokeh and depth of field have very little to do with subject isolation. Shorter focal lengths put your subject in a scene. If you use a 35mm lens, then your subject will have a place in a scene, you'll see the surroundings. Using a larger aperture blurs out the surroundings, but you'll still see the same amount. Using a large aperture also gives you less depth of field to work with, the transitions between subject and surrounding becomes blurred and you lose specular highlights. This might be the effect you're going for, however.
If you want to isolate your subject, i.e. to take them away from their surroundings, use a telephoto. The telephoto lens I used here was a Nikon 70-200mm f/4 VR, which is a mid-range priced 'prosumer' grade lens. This works just as well with a cheaper telephoto such as the Nikon (or Tamron) 70-300mm VR. If you want to do portraits and low light is not a concern for you, maybe take a look at one of those for isolation rather than something like a Nikon 85mm f/1.8G, which is more expensive.
Longer telephoto lenses have compression properties, they make people look more flattering because you're standing further away. That's a topic for another article, but they also have the very unique property of being able to separate the subject and background very decisively because they make the background so large and blown up. On top of that, unlike with shorter lenses where you have to use large apertures to give yourself that separation, telephoto lenses can do it with much larger apertures. Take a look at that shot above at f/22, look at how sharp and in focus the subject is and look at how that background is completely undistracting.
The takeaway point from all of this is that for bokeh and depth of field, it's all about the aperture, but bokeh and depth of field have very little to do with subject isolation. Shorter focal lengths put your subject in a scene. If you use a 35mm lens, then your subject will have a place in a scene, you'll see the surroundings. Using a larger aperture blurs out the surroundings, but you'll still see the same amount. Using a large aperture also gives you less depth of field to work with, the transitions between subject and surrounding becomes blurred and you lose specular highlights. This might be the effect you're going for, however.
If you want to isolate your subject, i.e. to take them away from their surroundings, use a telephoto. The telephoto lens I used here was a Nikon 70-200mm f/4 VR, which is a mid-range priced 'prosumer' grade lens. This works just as well with a cheaper telephoto such as the Nikon (or Tamron) 70-300mm VR. If you want to do portraits and low light is not a concern for you, maybe take a look at one of those for isolation rather than something like a Nikon 85mm f/1.8G, which is more expensive.