Strobe manufacturers typically publish the guide numbers of their strobes in air, but we wanted to test them in controlled conditions to see how they stacked up against one another. We especially wanted to see how they would perform with diffusers, as this is how we always shoot with our strobes when photographing wide angle scenes. Strobe,Sea & Sea YS-250,YS-D1,Z-240,comparison

Underwater Strobe Testing

Testing Methodology

Strobe manufacturers typically publish the guide numbers of their strobes in air, but we wanted to test them in controlled conditions to see how they stacked up against one another. We especially wanted to see how they would perform with diffusers, as this is how we always shoot with our strobes when photographing wide angle scenes. We also wanted to see how the strobes would perform across an entire frame; the evenness of the light is just as important as the intensity when lighting a wide angle reef scene.



For these tests, we used the same Sekonic Flash Meter in a room with the lights off. All strobes were tested at full power, ISO 100, at a distance of one meter, the same standard at which manufacturers also test their strobes.We wanted to test all manufacturers in the same conditions, measuring the relative differences in brightness between strobes.



While manufacturers quote the guide number at center, we calculated Guide Numbers across what would be a typical wide angle frame; at center, 12 inches out, and 18 inches out.



Interpreting These Results

The important thing to look at is the relative difference between the strobes, not the numerical value of the guide numbers. The guide numbers on the graph are f stop numbers, which are a ratio between lens length and opening, and are not an absolute measure of light. Each "stop" is double the amount of light. F32 to F22 is 1 stop of light, as is F22 to F16, and F16 to F11, etc. down the side of the graph. As the guide numbers decrease, the lens allows more light in, and the strobe does not need to emit as much light. As the number increases the lens opening is smaller and therefore the strobe needs to be brighter. All of our testing was with the strobe at full power.



This latest round of testing was prompted by the introduction of the Sea & Sea YS-D1 strobe which had a guide number specified from the manufacturer at F32, the same rating as Sea & Sea YS-250. We were surprised by the results in how close the guide numbers were comparing the Sea & Sea YS-D1 and Sea & Sea YS-250. When shot with diffusers, these strobes are about 1/4 stop difference in brightness. Since most cameras exposure adjustments are in increments of 1/3 stop, you would most likely not adjust the exposure between these strobes.



Out of all the strobes tested, Ikelite came closest to their published guide numbers.



Without Diffusers



Guide Numbers (1 meter in Air) - © Backscatter Underwater Video & Photo











With Diffusers



Guide Numbers (1 meter in Air) - © Backscatter Underwater Video & Photo



Strobes Tested in This Article









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