On camera flash restricts shutter speed

[Ricky21]

So, I guess I had never noted this until lately, but when the built in flash is up the shutter speed is restricted to 1/250. (60d). Does this have to do with recycling time of flash, or sync sipped or something? I use my speedlite 430 often, and have not noticed this before. Is this the same as well?

 

[TCampbell]

This is due to the fact that the focal plane shutter is mechanical. Some time is required to completely open. If the flash fires too soon, then only the part of the sensor which is exposed will receive the benefit of the flash.

The shutter has two halves called "curtains." In order to have a shutter speed faster than 1/250th, the camera has to start closing a second "curtain" before the first "curtain" has completely opened. Effectively it is sweeping a slit across the sensor. If the flash fired with the slit sweeping across, it would result in a narrow band of proper exposure in the frame and some dark underexposed areas.

The fact that you have a builtin flash doesn't matter. This mechanical restriction applies to all flashes because of the mechanical motion of the focal plane shutter. Continuous lights would not be affected by this (but they need to be pretty bright) since they're on all the time as the shutter curtains sweep across to expose the image. Flashes which support "high speed sync" pulse rapidly so that they expose the sensor evenly, but the catch is that they can't fire at full power.

(Edit: Had to fix a typo. I mean to say "continuous lights would NOT be affected" but I left out the word "not". <sigh> #drinkMoreCoffee)

 

[2WheelPhoto]

If you're willing to take your flash off camera and trigger with pocketwizards, 1/250th limitations don't apply and your flash will sync at full power at speeds of up to 1/8000th.

Google "pocketwizard hypersync" if you're interested.

That will work for your flash or studio type monolights.

 

[Big Mike]

Yes, this has to do with the camera's maximum flash sync speed (1/250) which is a limitation of the type of shutter that is in the camera.

HERE is a good example of what typically happens when you exceed the flash sync speed.

When you have your 430EX on camera, you have the option for something called High Speed Sync (HSS). This is a mode that causes the flash to use multiple pulses of light, rather than one blast. This allows you to shoot with flash at any shutter speed, but it also greatly reduces your output (working range). So in order for it to be effective, you have to be fairly close to your subject.