Sunstars at f/16: RF 14-35mm f/4L IS USM
A sunstar is not a filter effect. It is a diffraction phenomenon produced by the aperture blades of the lens when a point light source — the sun, a street lamp, a bare bulb — is included in the frame. The RF 14-35mm f/4L IS USM produces it cleanly. The technique is to use it intentionally rather than stumble into it.
The mechanics: at wide apertures, light bends minimally around the aperture blades. At f/11 and beyond, diffraction becomes significant, and each blade produces two rays. The RF 14-35mm has nine aperture blades, yielding an 18-pointed star. The shape, sharpness, and length of the rays depend on the blade count, blade curvature, and the aperture value. f/16 on this lens produces a crisp, symmetrical star that reads clearly at web resolution without requiring output at print size to appreciate.
The cost is diffraction softness across the frame. At f/16, the RF 14-35mm is measurably softer than at f/8. You are trading overall resolution for a compositional element. That trade is worth making when the sunstar anchors the frame — when it provides the viewer’s entry point, the sense of scale, or the graphic element that prevents a wide landscape from reading as empty.
The technique is positional. The sun must be partially occluded — by a tree branch, a building edge, a ridge line — so that only a sliver of the disc is visible. A full solar disc will not produce a star; it produces a large bright circle that overwhelms the frame. Partial occlusion controls the brightness and gives the rays room to extend. Shoot a series as the sun drops behind the obstruction, comparing the star character at different levels of coverage.
Expose for the mid-tones in the frame, not the star. The R5’s highlight alert will flash across the sun itself regardless — that is expected. The rest of the image should be correctly exposed. Bracket if the dynamic range of the scene is challenging.
The sunstar is a compositional device, not a special effect. Use it when the frame needs structure.