How can I photograph tiny seeds on a glossy white surface inside a wind tunnel with fewer reflections?
Asked 5/23/2023
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I need to photograph very small seeds as they disperse on a white sticky surface inside a long enclosed wind tunnel (about 400 × 100 × 70 cm). The tunnel interior is white and the sticky surface is reflective, so I’m getting glare and poor contrast. I currently use two LED light strips mounted high on both sides, aimed upward for indirect light. I painted the ceiling black to reduce reflections, but that also made the scene darker and less diffused. My camera is a Canon 700D with a 16mm lens, and I’m taking several overlapping shots along the tunnel length for later image analysis. How can I improve image quality so the seeds appear more clearly while minimizing reflections from the glossy surface?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
3y ago
2 Answers
1
What you want is for the ceiling and walls to be white, and the lights to be installed on the floor with a baffle to keep them from shining directly onto the reflective sticky surface.
When photographing reflective surfaces I find it easier to think of it as creating the environment that is going to be reflected, rather than as lighting the subject/object. And the goal of this is to create an evenly illuminated white box (walls/ceiling) for the surface to reflect (to illuminate the surface with diffused/reflected light). Preferably the entire ceiling would be white with only a small opening for the lens, because it is the ceiling that is going to be reflected.
If the lens opening is too much of a distraction (a dark circle reflection) you could resort to using an offset opening and a shift lens; but I do not think the surface is so reflective/critical as to require that.
Example diagram:
To hide the access strip in the top of the tunnel you could insert white posterboard between the sidewalls to create a domed ceiling; which would actually create more even/unified lighting. But that assumes that the inserts would be compatible with the airflow.
Originally by user70370. Source · Licensed CC BY-SA 4.0
user70370
3y ago
0
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Treat this as lighting a reflective surface by controlling what it reflects. A glossy floor will reflect the tunnel interior, so a dark ceiling often reduces glare but also removes the soft, even illumination you need.
Best approach from the answers: make the tunnel act more like an evenly lit white box. Keep walls/ceiling white, and use lighting that does not shine directly onto the sticky surface. Mount lights low or shield them with baffles so the floor mainly reflects large white surfaces, not bright strips. Angling the LED strips more steeply may also help keep direct light off the surface.
Also check focus carefully. The sample image may be slightly out of focus. Mark the floor plane with a laser pointer, then switch to manual focus and verify it stays accurate.
If you can alter the seeds, a strong alternative is fluorescence: dye the seeds, illuminate with blue light, and use a yellow/orange filter on the lens. That can make the seeds appear bright against a much darker background.
If the sticky surface itself can be changed, a more matte material would help the most.
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AI3y ago
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