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Finding Your Lens’ Sweet Spot

by Steph Doran (follow)
Blog (395)      Articles (166)     

You may have heard some photographers refer lovingly to the ‘sweet spot’ of their lens – that elusive combination of settings that provides users with an image that is somehow superior to all other images taken by that camera. But what exactly is a ‘sweet spot,’ and what does it do?

What Is A ‘Sweet Spot?’

The ‘sweet spot’ refers to the aperture setting at which your lens can produce the sharpest possible image. No matter what type of lens you have, not all apertures are created equally. Your lens will not produce the same level of sharpness across its entire range of apertures, and usually drops off at the extreme ends of the scale. For example, when you shoot with your highest (eg: f.1.2) or lowest aperture setting (eg: f.22), you may notice that your images just aren’t as sharp as when you shoot with a mid-range aperture (eg: f.8), even when you have nailed the focus. This is because the lens is not working within its prime range. Usually, a lens’ sweet spot will sit within the mid-range apertures (usually f.8-f.11.)

When discussing the ‘sweet spot’, it’s important not to confuse sharpness with depth of field. Depth of field refers to the range of distance that appears in focus, from the foreground to the background. We know that depth of field can be controlled by adjusting our aperture, to make the background of our images more or less focused.

But sharpness refers to the overall clarity of detail in an image, and not ‘how much’ of the shot is in focus. It may help to think of ‘sharpness’ in terms of quality, and ‘depth of field’ in terms of quantity. When finding your ‘sweet spot’, you are looking for the aperture that provides the greatest sharpness to the focal point of the image.

How To Find Your Sweet Spot

Thanks to the internet, a simple Google search will let you find your lens’ sweet spot within minutes. Just type in your lens model and “sweet spot.” Many online reviews detail the sweet spot of a lens, which the authors have usually discovered by testing it themselves. But why take their word for it? Conducting your own ‘sweet spot test’ is really easy, and it will make you much more familiar and confident with your own gear. The sweet spot of your lens may also vary slightly from the online reviews, depending on the sensor your camera contains.

Here’s a simple test to determine your lens’ sweet spot:

1) Set up your camera on a tripod to take multiple pictures of the same scene. A tripod will give you the stability you need to do this and it will much more difficult to compare images without this consistency.

2) Set up a piece of paper with printed text on it, and point the camera at it. A page from a newspaper works quite well. Text makes for a good subject, as we are more readily able to recognise differences in text sharpness, compared to more organic subjects. Also, it won’t move, but just make sure it’s flat.

3) Point your lens directly at the paper, and focus on it.

4) Take a series of images of the paper – one at each full aperture stop (eg: f4, f5.6, f8, f11, etc.). It helps to use a remote trigger or self-timer, to avoid camera shake.

5) Load the images onto your computer and compare the shots. Make sure to look at the images at 100% resolution (ie: zoom in to 100%).

What are you looking for exactly? You’re trying to find the images in which you can see the best overall sharpness, from the entire range of images you’ve taken. Once again, don’t confuse ‘sharpness’ with ‘depth of field’. Don’t only look at the centre of the image, but also pay attention to the edges and the corners of the shot. The sweet spot is the aperture where the detail in all three areas is best.

You may notice that there’s no single aperture that has the ‘best’ sharpness, but rather, a range of them. This is normal. Usually, it will be the apertures in the middle of the range that will be ‘sweet’, with sharpness falling off as the aperture becomes wide open, or very closed down. In this case, you may find that your sweet spot is, for example, ‘f.8-f.11’ rather than just ‘f.8’ only.

If you have a zoom lens, the test becomes a little more complicated, because a zoom lens is capable of working at different focal lengths. Zoom lenses will have different sweet spots, depending on the chosen focal length. To determine the sweet spot for this type of lens, conduct the same test as above for each major focal length. It will be more time consuming, but be methodical in your approach.

When To Use The Sweet Spot

Now that you know where your lens’ sweet spot lies, don’t feel like you can only shoot within the ‘sweet’ range of apertures. Exposure, image composition and emotion should all come before ‘using the sweet spot’, in terms of importance. It’s completely acceptable to push your lens to its minimum or maximum aperture – but the ‘sweet spot’ is a great point to be aware of, especially if you require particularly sharp imagery. Just don’t let it restrict your shooting style or your enjoyment of photography.

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