Tips for creating sunstar images
In photography, sunstars are images of either the sun or a bright light source like a sodium vapour lamp, which appears as pointed star shapes. One such image of a light house at sunset is shown here.
Sunstars can be created by using a small aperture of the lens. The pointed lines are a result of diffraction, which is generally hated in the photography community. However, if diffraction is used correctly, it can create interesting sunstars with very low loss in image sharpness (when viewed 100%). It makes a bright light photograph more interesting. The resulting image has an artistic effect because of the sunstars. Here are some tips to create sunstars in an image.
Equipment: A camera which can easily modify the aperture of the lens (cropped-frame, full-frame DSLRs or medium-format, your choice). The lens should preferably have odd number of diaphragm blades. Most DSLR lenses have 5-9 blades. The odd number of diaphragm blades results in doubling the number of sunstar lines you get. For landscape photographers, the Tokina 11-16 mm f/2.8 is a good choice because of its 9 blades, apart from being a good quality lens. A tripod, to be able to take photos at low speed. Optional: 2- or 3-stop graduated neutral density filter to reduce the intensity of the light source.
Camera settings: Mount your camera on a tripod to provide stability. Set the camera to either Aperture mode or Manual mode. In bright light, the ISO can be set to a low of 100 or 200. Compose the image such that the bright source of the light (like the sun or a bright lamp) is well in the frame of the image. Otherwise the sunstars may get cropped out in the final post-processing. For getting good sunstars, set the aperture to a small value. In cropped-sensor cameras, this is around f/7.1 - f/9. Even f/11 may be fine, but beyond that the effects of diffraction are more obvious. You may need to adjust exposure compensation to darken the surroundings to avoid blowing out of the highlights of the sun. Shoot till your heart's content.
Post-processing: You will have to mostly correct for the exposure, without blowing out the highlights of the light source and re-compose for a better looking image.
Photo credits: Vinay Bavdekar.