 Scott McCord |
Faster shutter speed with flash? I have the canon 70-200mm and am now needing to use it frequently in situations where I need to use flash as well. I know that when this lens is zoomed up that I need at least 1/200 shutter speed, but I'm finding that I actually need to go even faster to keep sharp images. However, the flash keeps my shutter speed at 1/200 because of the sync speed. Is there a trick to allow you to increse your shutter speed over 1/200 while still using your hot-shoe mounted flash? And FYI, I can't always use a tripod because I'm constantly moving around.
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Jon Close |
You need a hot-shoe mounted flash that is capable of FP High Speed Sync, such as any of the Canon EX-series speedlites, or similar from Sigma (EF 500 DG Super) or other makers.
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Alan N. Marcus |
Hi Scott, I looked up the specifications for your Canon and you are correct, X-sync is 1/200 and the guide number at 100 ISO is 43. That means you can’t take flash pictures when set to faster shutter speeds. To use the guide number see below. Now the in-camera flash sports a guide number of 43 at 100 ISO. We use this value to calculate the aperture needed at different distances. Now your 70-200mm zoom is generous, when mounted on your camera its equivalent to a 105 – 300 if mounted on a 35mm. I am telling you this because most times, with this lens, you’re subject to camera distance will be lengthy. I think that in most instances you will likely exceed the reach of the on-camera flash. Stated in a different way, if the subject is more than 25 feet away, the flash effect will be zilch. There are no tricks available except when shooing in dim light, whereby the flash will be the principle light source, you don’t need to worry much about shutter speed. You see, the flash duration is very very short and if this is the only light, the subject will be frozen. Try shooting an electric fan in a darkened room, the motion of the fan blades will be arrested. Lick to you, Alan Marcus
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Scott McCord |
Thanks guys - good info. Alan, just to let you know, my external flash is a canon 550EX. I normally have the flash on ETTL mode, and I always have the shutter speed at 200 when using the 70-200 f/2.8 - that is if there's enough light. After reading your explanation, I think the reason I was getting soft shots even at 200 with the flash is that the ETTL was not allowing the flash to put out enough light. So, if I switch to manual output, at say 1/2 power, on my flash to increase the range of power, I should remedy the soft shots. Am I correct in assuming this? I knew I should have shelled out the extra for the IS. Oh - and just noticed your funny typo in your salutation, Alan. That's a very friendly greeting!
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Alan N. Marcus |
I want to assure everyone it was a typo! Alan Marcus
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Alan N. Marcus |
I think you are right on target. Consider that each time you double the distance, subject to lamp, the fall-off is 4x. Stated another way: All point sources follow the law of the inverse square. Change lamp to subject distant, say 8 feet to 16 feet – light arrives at subject 16 feet away at only 25% of the intensity that it did at 8 feet. That’s 2 f/stops less each time subject to lamp distance is doubled meaning you must open up 2 f/stops Luck to you, Alan Marcus
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Samuel Smith |
i was wondering about the...typo?
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