@Lesnums) Posted on 13/01/18 at 09:30 Share:
When a light source appears in the frame of a photo, its appearance can take on the appearance – depending on the shooting conditions and settings – of a simple luminous spot or of a more complex shape resembling a a star with multiple rays. Far from being the result of chance, this radiation called star burst effect can be easily reproduced. Here are some tips to help you practice. We obviously invite you to post your results in the comments of this article on the Focus Numérique Facebook page.
The principle
Although it is sometimes best to avoid it, the starburst effect is an interesting graphic element. Applied to a daytime scene, it gives the sun an aspect close to its drawn representations and can constitute a point of attachment for the spectator's gaze when the texture of the sky is not very interesting. When applied to a night scene, it then touches street lamps and other night lights, and then lightens the dark mood somewhat to give a more dreamlike atmosphere.
Photo : Scott Webb.
The starburst effect is intimately linked to the optical phenomenon called diffraction. As explained in more detail in our article dedicated to this subject, light sometimes behaves like a wave and can therefore interfere with surrounding elements. The edge of an object or a small hole – such as the diaphragm of a lens – can thus alter the direction of the light. Undesirable in most photographic cases, because it causes a loss of sharpness, diffraction however creates what is called the starburst effect when certain conditions are met, namely the use of a low diaphragm opening and the presence from a relatively distant light source.
Practical details
The more the lens diaphragm is closed and polygonal in shape (rather than spherical when open), the stronger the intensity of the light rays that characterize the starburst effect. To let these appear in the image, it is therefore advisable to choose a low diaphragm opening. To obtain a starburst effect while limiting the loss of sharpness due to diffraction, we advise you to opt for an aperture of diaphragm between f/11 and f/22.
Although your impact on this factor at the time of shooting is nil, note that the number of rays of light that make up the starburst effect depends on the number of blades that make up the diaphragm of the lens you are using. If the number of lamellae is even, the number of rays y will be equal. If the number of slats is odd, the number of rays will be twice as many. The optical formula and the treatment of the lenses of an optics influencing the sharpness of the rays, we invite you to carry out tests to determine which of your lenses is best suited to the desired effect.
Photo: Muhd Asyraaf.
If you try the starburst effect in broad daylight and incorporate the sun into your composition, be aware that the effect will be more pronounced when the light source is partially obscured by an element of the environment. Also keep in mind that you should protect your eyes as well as your device (sensor and shutter) from the very strong light intensity. Just as in the case of a solar eclipse, the use of a screen or an electronic viewfinder is essential for observing the star through your device, while the use of filters specialized optics can be paramount to its capture.
In the middle of the night, the technical constraints are different: the low luminosity and the adoption of a small diaphragm opening entailing – to obtain a good exposure – the use of a long exposure time, you often need to bring a tripod to create a starburst effect while avoiding any risk of camera shake.
Conclusion
Photo : Xuqing Jia.
If your lenses do not allow you to obtain a sufficiently pronounced starburst effect for your taste, or if you are somewhat nostalgic for the photo aesthetic of the 1970s, be aware that optical filters bearing the name Star are specialized in this effect. . However, their use is accompanied by a loss of sharpness due to the diffraction phenomenon they cause.
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