Ask the Expert: Sweet Spot of a Lens
This story was originally published in Septemeber 2011.
What is the meaning of sweet spot? How does one determine the sweet spot of a lens and use it to improve photographs?
Ritesh Sadarangani, Shillong
A lens does not have the same sharpness throughout the complete aperture range. The sweet spot of a lens is simply the aperture value at which the lens is at its sharpest. For instance, most lenses are slightly soft at wide apertures like f/3.5. These lenses become sharper by stopping down to an aperture like f/8. However, the lens starts becoming soft again at narrower apertures like f/16 due to diffraction.
Usually, the sweet stop of a lens is somewhere in the middle of its aperture range. To actually determine the sweet spot of your lens, you will need to shoot a resolution chart at various aperture values. Select the Aperture Priority mode and set your camera on a tripod, use a remote trigger or cable release to eliminate camera shake. Start shooting at the widest aperture and keep increasing the value by one stop such as f/2.8, f/4, f/5.6 and so on. View the images on the computer and determine which image looks the sharpest.
Identifying the sweet spot does not mean that you must shoot only at that particular aperture value. Some scenes might require the use of shallow depth-of-field and hence, a wide aperture, while other situations might need a narrow aperture value due to bright lighting conditions. However, when you do not need to use an extreme aperture like f/2.8 or f/22, and want the best possible sharpness, you can simply set the lens to its sweet spot and shoot.