Flash Sync Speed

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Revet

Senior Member
Pretty cool Gaff!! I also like that section on freezing things with the flash also. It makes so much sense. Use the flash as your main or only light source will freeze the motion, so turn that ambient down using near max sync speed and we should be good to go with a nice frozen image of something in motion. I too will await Wayne's response on the above pictures because I would have thought the first one should be crisp if you had no ambient lighting the flowers (I think that's what they are). I'm curious about the exposure in pictures 2 and 3, you went down 2 stops (one in shutter speed and one in ISO), but the exposure looks the same. We know that shutter speed doesn't affect the flash exposure but ISO should have. Was the flash still at 1/16 power for the 3rd picture or did it increase to compensate for the one stop reduction in the ISO?? Also note that at that low power, you did get a blue tinge to the photo as mentioned in Wayne's presentation.

OK I just read the bounce section. Great presentation!! It will change how I take photo's. Here is a question I have which may not interest other photographers, but may interest other tecky Geeks like myself. Going back to physics, When light hits an object, some light is absorbed, some reflected, and some might pass through pending the material it is hitting. In any case, the reflected light loses energy (not speed because the speed of light is a constant). You have made it quite clear that we are losing power with bounce which to me would be the amplitude of the light wave. How about frequency? A lower frequency light wave (ie. more red) also has less energy. Does this happen when we bounce or do we mostly just lose amplitude??
 
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thegaffney

Senior Member
The ceiling is probably about 12ft high, so probably lost a lot more than if it was shorter.

The other 2 pictures I did change the flash power so that the exposure matched the first one, the flash was around 1/4 to 1/2 I think. I didn't have to change it from the second to the third though.

I'll try it again at the 1/10 speed, maybe something was funky, I also think it should of been as sharp

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WayneF

Senior Member
Revet said:
Going back to physics, When light hits an object, some light is absorbed, some reflected, and some might pass through pending the material it is hitting. In any case, the reflected light loses energy (not speed because the speed of light is a constant). You have made it quite clear that we are losing power with bounce which to me would be the amplitude of the light wave. How about frequency? A lower frequency light wave (ie. more red) also has less energy. Does this happen when we bounce or do we mostly just lose amplitude??
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I doubt the bounce suffers red shift unless the ceiling is accelerating. :) Joking, but no, I am not aware of anything except it can take on a color tint reflecting from a non-neutrally colored surface ( bounce it on a red wall, and it will become significantly red). Many ceilings are white enough to not be a big problem, but use of a white card to be sure is always helpful to get White Balance exact. Getting white balance and exposure just right is always that last straw that makes so much difference.

We certainly do lose power from bounce. The travel path up and down (and the trig to go forward to the subject too) is a significantly longer path than the direct line, so inverse square law makes a difference. Also the ceiling has a reflection coefficient. A white popcorn ceiling would be higher that a 18% card, but not very near 100%. The best smooth white card is only about 90% reflectance, so I'd guess maybe 65%, but I really have no idea. Dispersal over the wider room is also a major factor, dispersal dilutes the beam, it takes power to fill a wide area to the same brightness as a small concentrated beam. Depends on the situation of course, but overall, common bounce probably often needs about three stops more power than direct, which is 8x power. We can't ever have too much power for bounce. :)

We usually called it two stops more for bounce, back in the old days of film and flash bulbs and no metering and no test shot results. The only reason it worked was because negative film had so much more latitude - it was hard to do much wrong.
 
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WayneF

Senior Member
thegaffney said:
Did it again at 1/10, this time it looks just as good as the other ones, so thats odd. Oh well it was fun now I know I can do that :)
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Well, that's good. :) The numbers do seem suspect, I just cannot imagine bounce on a 12 foot ceiling with ISO 400 and f/11. Possibly f/4? And full power level is NOT fast. Fast needs a lower power level, and needs any continuous ambient to be dim, that won't blur what the flash stopped.

Here is a sample that shows the speedlight speed at various power levels

Capability of flash units for high speed photography

This shutter was open about 1.5 seconds. It was in a dim room, but not dark. There was a regular table lamp on across the room, but at ISO 100 f/16, the frame was dark.
 
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thegaffney

Senior Member
WayneF said:
Well, that's good. :) The numbers do seem suspect, I just cannot imagine bounce on a 12 foot ceiling with ISO 400 and f/11. Possibly f/4? And full power level is NOT fast. Fast needs a lower power level, and needs any continuous ambient to be dim, that won't blur what the flash stopped.

Here is a sample that shows the speedlight speed at various power levels

Capability of flash units for high speed photography

This shutter was open about 1.5 seconds. It was in a dim room, but not dark. There was a regular table lamp on across the room, but at ISO 100 f/16, the frame was dark.
Click to expand...

Yeah you are right, when I re-did the shot I had to set the flash to 1/4 power, I really need to right this stuff down while im testing, I remembered all the other settings though
 
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