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1

We use the Guide Number as an aid to gauge the f-number setting. Accept, as an example, your ISO setting is 200. You consult a table of guide numbers and discover it’s 180. Your principal subject is 10 feet downstream of the flash. What would be the appropriate f-number setting? To compute, we divide guide number by distance -- thus 150 ÷ 10 = 15.5. Now ...


1

Both of the other answers are correct, but I think there might be an easier way to understand it: Consider being in a completely black room with no light... the shutter can be open indefinitely because there is no light available. The only thing that matters is that the shutter is fully open when the flash fires so that all of the sensor can see it. The ...


5

The simple equation assumes that the flash is effectively the only source of light in your image. This is a reasonable assumption in many cases, because since exposure works on an exponential scale, the amount of light from typical indoor room lighting is a drop in a bucket compared to that provided by the flash. See Do flash guide numbers assume some ...


11

Flash duration is typically much shorter than most cameras' flash sync speed. If the flash only has a duration of, say, 1/1000 second (or 1 millisecond), it matters not if the shutter is open 1/250 second (4 milliseconds) or 1/25 second (40 milliseconds), the energy from the flash that is captured by the photo will be the same in either case. What shutter ...


22

It's hard to really tell from the small versions here — which is a lesson in itself, because at 1280x850, which is a perfectly fine online viewing size, the differences really don't matter that much. However, in this case, I think Auto probably did make some better choices. Shutter Speed You picked ¹⁄₆₀th of a second. This is fine, but probably slightly ...


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