File :-(, x, )
flash and freezing motion Anonymous
does flash let you have a slower shutter speed and freeze motion than without?

as in, you need 1/500 but that gives you a super underexposed picture

but if you had a flash, you could take it at 1/125 and be okay with everything ice cold frozen (no trailing blur)
>> ac !!VPzQAxYPAMA
     File :-(, x)
...kind of.

Basically, when you're shooting with flash, it's as if you're exposing the picture twice. Once for the bit the flash hits, once for everything else in the frame. The flash part of the exposure is dictated by the flash power, the aperture, and the ISO--shutter speed doesn't really enter into it as long as you're slower than the flash sync speed for your camera.

So there are two possibilities:
1. You take the picture with a fast shutter speed. The flash lights up as much as it can, but you get that standard "Brightly lit person in a tunnel" look common to P&S cameras and onboard flash
2. You take the picture with a slow shutter speed. The main subject gets burned in significantly, by the flash, but there's still a little bit of exposure after the flash that blurs the edges a bit, especially if they move at all. Background burns in more slowly thanks to available light.

Attached is a pic taken with a fairly slow 1/13th shutter and crappy on-camera flash to show you what it looks like when you do that.

Camera-Specific Properties:Equipment MakeCanonCamera ModelCanon EOS DIGITAL REBEL XTiFirmware VersionFirmware 1.0.5Owner NameunknownSerial Number0420104373Image-Specific Properties:Image OrientationTop, Left-HandHorizontal Resolution72 dpiVertical Resolution72 dpiImage Created2007:07:20 22:09:54Exposure Time1/13 secF-Numberf/2.0Exposure ProgramAperture PriorityISO Speed Rating1600Lens Aperturef/2.0Exposure Bias0 EVFlashFlash, CompulsoryFocal Length35.00 mmColor Space InformationsRGBImage Width3888Image Height2592RenderingNormalExposure ModeAutoScene Capture TypeStandardExposure ModeAv-PriorityFocus TypeAutoMetering ModeEvaluativeSharpnessUnknownSaturationUnknownContrastUnknownShooting ModeManualImage SizeLargeFocus ModeOne-ShotDrive ModeSingleFlash ModeOnCompression SettingFineMacro ModeNormalWhite BalanceAutoExposure Compensation3Sensor ISO Speed288Camera Actuations-328335248Color Matrix34
>> Anonymous
- The flash strobe itself is so short that it's *guaranteed* to freeze any motion it illuminates.
- When using a flash, the shutter speed must not be faster than some value determined by the shutter construction, in order for the shutter to be fully open at the time the flash fires.
- Flash strobe, obviously, adds to the ambient light and not replaces it. So if blurry object trails are already visible at your 1/125s shutter speed without flash, you'll also get them with it.
>> Anonymous
That is technically impossible. Although the flash might freeze an actual sequence of the picture, this will result in motion blur.

The flash will light the sequence for that particular time (e.g 1/125th), but the motion blur is exactly the same as with 1/125th without flash.

The flash does not affect the light coming through the lens (e.g will not change the motion of water during that time)
>> ac !!VPzQAxYPAMA
>>172475
>The flash will light the sequence for that particular time (e.g 1/125th), but the motion blur is exactly the same as with 1/125th without flash.
The flash actually lights the sequence for however long the flash takes to fire, which is going to be significantly less than 1/125th of a second. So if the surroundings are dim enough that the remainder of the 1/125th doesn't impinge on the exposure, it will freeze the motion.

That's how they take pictures of things like bullets hitting apples--they actually leave the thing open in bulb mode and have a flash set up to fire as soon as the bullet hits.
>> Anonymous
>>172475
>The flash will light the sequence for that particular time (e.g 1/125th)

No. A regular flash strobe lasts around a dozen microseconds. (although some new flashes have a mode that allows them to work with focal plane shutters at fast shutter speeds by emitting strobes at high frequency, which actually gives an effect of constant illumination)
>> Anonymous
but on my flash, even the manual setting, i can only dictate it's power output like 1:1 down to 1:128 i think

there's no way for me to change the flash duration

is that why people say that even manual flash is still automatic because the flash chooses the duration itself?
>> ac !!VPzQAxYPAMA
>>172484
I think the duration is mostly fixed. And very, very fast.
>> Serenar !m827jEgWi.
>>172484
Duration doesn't change, only power.
>> Anonymous
>>172485
>>172698
Flash duration is not fixed. That's how power output is controlled. The actual luminance per unit time is constant, to get lower powers the flash fires for a shorter duration.
>> Anonymous
>>172718
this man speaks truth
>> Anonymous
>>172718

so tell me if i get it right... the manual setting in the flash dictates the DURATION of the flash emitted, NOT the POWER of the flash?

ps: where does flash compensation work, when does it come in?
>> Anonymous
>>172718
then why is it possible to see a difference in the brightness of the flash if its just changing the duration?
>> Anonymous
     File :-(, x)
I just took two pictures with my A520. One with flash at full and one with flash at minimum. Both at 1/200 seconds (and I forgot to set the aperture).

Here is the one with min flash.

Camera-Specific Properties:Equipment MakeCanonCamera ModelCanon PowerShot A520Maximum Lens Aperturef/2.6Sensing MethodOne-Chip Color AreaImage-Specific Properties:Image OrientationTop, Left-HandHorizontal Resolution180 dpiVertical Resolution180 dpiImage Created2008:04:30 21:18:20RenderingNormalExposure ModeManualWhite BalanceAutoScene Capture TypeStandardExposure Time1/200 secF-Numberf/5.0Lens Aperturef/5.0Exposure Bias0 EVMetering ModePatternFlashFlash, Compulsory, Red-Eye ReduceFocal Length5.81 mmColor Space InformationsRGBImage Width1600Image Height1200Image Number153-5322
>> Anonymous
     File :-(, x)
>>172787
And here is with max flash output.

I'm not sure what this proves, but it looks as if the room wasn't even lit with min flash. This may be just due to the flash being too short for the camera to capture at this ISO, or else it is actually less bright. At full flash, it certainly seemed much /brighter/, but that may be a trick on the eyes.

Camera-Specific Properties:Equipment MakeCanonCamera ModelCanon PowerShot A520Maximum Lens Aperturef/2.6Sensing MethodOne-Chip Color AreaImage-Specific Properties:Image OrientationTop, Left-HandHorizontal Resolution180 dpiVertical Resolution180 dpiImage Created2008:04:30 21:18:32RenderingNormalExposure ModeManualWhite BalanceAutoScene Capture TypeStandardExposure Time1/200 secF-Numberf/5.0Lens Aperturef/5.0Exposure Bias0 EVMetering ModePatternFlashFlash, Compulsory, Red-Eye ReduceFocal Length5.81 mmColor Space InformationsRGBImage Width1600Image Height1200Image Number153-5323
>> Anonymous
>>172789
By short, I meant in time. However, I always thought that a stronger flash actually made the distance increase. This would be due to a brighter flash, not a longer one (I assume).
>> Anonymous
>>172790
The flash strobe varies both in duration and brightness. But since the duration is in microsecond range, nobody ever measures them separately, they measure total light output during the strobe and recalculate it into guide numbers (GN).