Do smaller grid cells make a speedlite grid dimmer, or just narrower?
Asked 5/16/2013
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If I make a DIY speedlite grid from black straws, changing either the straw length or the straw diameter will narrow the beam. But does reducing the cell diameter also reduce the brightness of the main illuminated spot, not just the spread?
My thought is that each straw only lets part of the flash tube be seen from the wall. If the straw opening gets smaller, each cell passes light from a smaller portion of the source, so it seems like the centre of the projected spot should get dimmer as well. I’m only asking about the main evenly lit area, not the falloff at the edges.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
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Yes, with the black straws, it is going to absorb most of the light that does not go directly through the straws. The smaller in diameter the straws, the more direct the light has to be traveling to get through and the more light will be absorbed.
If the straws were white, it would actually get brighter as the reflected light would be more focused, but it would also have more light reflecting from the edges, so it would be less co-linear and thus softer.
Also, be careful about getting the straws too close to the speedlite. At close distances, speedlites can get very hot and could actually melt the plastic.
Update: Ok, going back and seeing that the question was actually about not only diameter but depth as well. The closer to co-linear the light needs to be, the less light will get through. This will happen with length or diameter. Smaller diameter is going to mean slightly more material blocking light from entering at the entrance, though it's a fairly small amount of additional light being blocked.
Originally by user11392. Source · Licensed CC BY-SA 4.0
user11392
13y ago
0
Generated from our catalog & community — verify before relying on it.
Yes—generally, a tighter grid becomes dimmer as well as narrower, especially with black straws or other non-reflective cells.
Why: smaller-diameter cells and/or longer cells require the light to travel more nearly straight through. More off-axis light hits the cell walls and is absorbed instead of reaching the subject. So a black grid wastes more light as it gets tighter.
For a small source like a speedlite, making the individual cells smaller does not necessarily reduce the centre brightness by very much on its own, because more cells fit into the same area and can contribute to the central spot. But in practice, wall thickness and absorption still cause light loss, and increasing depth makes that loss more noticeable.
If the cell interiors were reflective (for example white), more light could be redirected forward, but the beam would also become less clean and a bit softer/less collimated.
So the short answer is: tighter grids usually mean both a narrower beam and less output, with black grids showing the most loss.
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