Why f/2.8 is great, mate…

For those of you with lenses that enable you to shoot at f/2.8, here’s a question (two actually) we’d like to ask you, writes Andrew James and Jon Adams.
Why do you shoot at f/2.8 and how often?

In preparing for this feature, AJ used Lightroom’s search by metadata to isolate any image in his current catalogue that was taken at f/2.8, regardless of lens type. The result was over 9000 frames at f/2.8.

Before digital came along, opening up the aperture to the widest a lens could offer was the only way to gain extra light, because the ISO of the film was fixed when in the camera. These days we can change ISO from shot to shot, so other than not wanting to increase ISO in case it results in excessive image noise, upping the ISO rather than changing aperture is frequently the better option.

It’s pretty clear that improvements in high ISO performance mean the main reason to shoot any subject at f/2.8 is – 99 times out of 100 – purely a creative one. There are exceptions, though. For example, astrophotography uses fast apertures to capture star details in the night sky because even at a high ISO, a wide aperture is still needed to suck in every little morsel of starlight! But extremes aside, the role of f/2.8 (and wider apertures if you have them available) is now almost exclusively a creative one.

But before we get to the creative, here’s a quick refresher on how aperture works…

What’s going on under the bonnet?
Inside every lens is a diaphragm that can be opened or closed to change the size of the hole in the middle. This hole lets more or less light through, depending on how large it is, so whether the scene is bright or dim, you can control the amount of light to make a good exposure. The aperture value itself is labelled in f/numbers (like f/2.8, f/4, f/5.6, etc), and these slightly weird numbers express the ratio between the focal length of the lens and size of the opening.

Wide open at maximum aperture with the diaphragm blades out of the way, a 300mm lens would have a ‘hole’ with a diameter of 107mm, and a 24mm lens would have a ‘hole’ measuring around 8.6mm. So, although the two lenses and the physical apertures are completely different sizes, what’s common is the ratio of the focal length divided by the ‘hole’ diameter, and this commonality means that the f-stop on one camera with one lens will give us the same exposure as the same f-stop on another camera with any other lens, provided the shutter speed and ISO settings are consistent.

The aperture value choices on a lens are always limited by the lens’s size and construction, so on most lenses you’ll see a range of about 6 or 7 ‘stops’, from f/2.8 to f/22. The difference between each ‘stop’ is a halving of the light that’s allowed through, so f/4, for example, lets half as much light through as f/2.8, and f/5.6 lets half that of f/4. Cameras allow you to break each stop down even more though, to either 1/2 or 1/3 stop amounts, so you get loads of control over the quantity of light that gets through.

Getting creative with f/2.8
What does f/2.8 give you? Used wisely, it gives you an image that just looks good in a cinematic way. It’s the contrast between a shallow area of sharp focus and a large area of blur that makes the image visually interesting. It’s a way to direct the viewer’s eye quickly to a specific point because our eyes seek out the area that is acceptably sharp, even if it’s only a small part within the frame. It gives you visual control over how you want the viewer to see the scene you are capturing.

But it also has some downsides. Get the focus wrong, and your f/2.8 shot can look a mess. On other occasions f/2.8 simply won’t give you enough detail to make an image work. For example, it’s not totally unheard of to shoot a wide-angle landscape image at f/2.8, but it would very much be the exception because often, that kind of subject and scene stands or falls on the depth of its detail, from front to back.

At f/2.8 there is also a drop off in image quality because you’re not shooting at the sweetspot of the lens, which is typically two or three stops up from its maximum apertures – that’s f/5.6 or f/8 on a f/2.8 lens.

Portraits are the most obvious subject for the f/2.8 treatment. You know the drill here Foto-Buzzers, focus on the eyes (or lead eye) at f/2.8 using a short telephoto lens and you get a gorgeous drop off in focus behind. The front of the nose can blur, softening it slightly, while even the ear is soft, leaving this nice small zone of sharpness that makes the subject’s look even more intense and engaging. The viewer can’t help but look them the right in the eye! You can see how it works on this portrait of an Indian man. Don’t forget to scroll between the two images.

But f/2.8 really isn’t limited to portrait photography; it can have its moment in almost any genre you can think of. In this reportage shot, it’s been used to isolate the two men running out of the rain. Fine detail isn’t important here, it’s about capturing the moment quickly and with a fast enough shutter speed.

It can work for wildlife too, but you need to be careful, as often you’ll need deeper sharpness to capture all the detail you want. But f/2.8 was the right aperture choice for this King Penguin chick. The main bird needed isolating from the group behind to make the most of its shape, further accentuated by the backlighting. The wide aperture did this perfectly, while at the same time retaining enough textural detail in its feathers. The beak is sharp, but only because AJ waited until it looked to one side.

The same isolation technique is used for this telephoto landscape shot. By focusing on the lead tree, it’s separated from those in the background and the image becomes more about pattern than depth of detail.

You’re less likely to use f/2.8 when shooting a building, but it works here by reducing the fine detail and accentuating the shapes and patterns.

Finally, with more detail created by a smaller aperture, this shot would be very boring indeed. But f/2.8 draws the eye to the flower, and the vase becomes nothing more than an interesting blue circle set against the flat grey of the concrete it’s sitting on. This is where f/2.8 excels because it can almost create something arty from nothing.

There’s no doubt that f/2.8 isn’t always the obvious choice and you need to avoid the pitfalls we mentioned earlier, but it can lead to some really creative images.

Here’s a suggestion… Grab a lens that has a wide aperture – obviously f/2.8 is ideal but if your lens isn’t that fast then f/4 is a good compromise – and head off for a walk somewhere. Shoot everything at the maximum aperture, thinking carefully about your focus and its relationship to the rest of the image. Your results might surprise you.

Published in Camera Skills
  1. One for the money, oofa the show ….

  2. Good one. I’m going to give this a go when I next get out with the camera.

  3. I’ve given up the habit but we still have some packs floating around. The risk to eyesight warning seemed appropriate for a photo with an aperture of f/1.2

  4. Thank you for some great tips!

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