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E-TTl 2 Exposure Compensation
  
 
mrwxyz
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p.1 #1 · p.1 #1 · E-TTl 2 Exposure Compensation


Basic question from one who is new to flash photography.

If shutter speed is 1/60 sec for a lighting condition , will it improve if we use E-TTL 2 capable flash.

What I am seeing is adding a flash does not improve the shutter speed(I am using Canon 5D classic).



Jun 04, 2014 at 05:51 PM
BrianO
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p.1 #2 · p.1 #2 · E-TTl 2 Exposure Compensation


First of all, what do you mean by "improve the shutter speed"? Do you mean allow a faster shutter speed?

Flash essentially has no effect on shutter speed in and of itself, and shutter speed has no effect on flash. Flash adds a vey fast burst of light, much faster than any standard shutter. What the extra light allows is lower ISO settings and/or smaller apertures.

If you were in a totally dark room and lit a subject with only flash, if wouldn't matter if the shutter was open for 1/250 second or for one hour: the subject would be lit with the same 1/1000-second (or whatever) burst of flash.

In reality, we rarely shoot in total darkness, so the shutter speed does matter because slower shutters will allow more of the ambient light to record in addition to the flash.

Going in the other direction, too fast of a shutter speed can cause problems if it is faster than the camera's maximum "flash sync speed," because at higher speeds the shutter is never fully open. Instead a moving slit of partially-open shutter curtain moves across the sensor or film, exposing only part of it to the ambient light at any moment. The flash pulse will only light up part of the scene in that case, the part under the slit at the moment the flash fires. Everything else will be lit only by the ambient, and so will be under exposed.

Now, back to the question: let's say you're shooting a wedding reception, and you want a picture of the bridal couple dancing. The room is fairly dark, and if you shoot at ISO 800 and f/5.6 the ambient light requires 1/60 shutter speed. If you add flash, there's enough light to shoot at 1/125, which reduces motion blur a bit better than 1/60.

When you say "What I am seeing is adding a flash does not improve the shutter speed" can you give more detail on what you mean? What are you shooting, under what conditions are you shooting, and what settings are you using?



Jun 05, 2014 at 09:06 AM
mrwxyz
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p.1 #3 · p.1 #3 · E-TTl 2 Exposure Compensation


Thank for the explanation.

I thought Exposure Compensation takes flash also in to consideration.
I was expecting higher shutter speed using flash , which was a wrong assumption.



Jun 05, 2014 at 01:53 PM
BrianO
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p.1 #4 · p.1 #4 · E-TTl 2 Exposure Compensation


mrwxyz wrote:
I thought Exposure Compensation takes flash also in to consideration. I was expecting higher shutter speed using flash , which was a wrong assumption.


You may get higher shutter speeds, depending on the selected exposure mode, for the reasons stated above. What exposure modes are you using? I usually use Manual Exposure with Automatic flash (ETTL). Some Autoexposure modes lock the shutter at one speed when a flash unit is detected in the hot shoe. I prefer the control over shutter speed and aperture that Manual mode gives me, combined with the flexibility that ETTL autoflash gives over varying flash-to-subject distances.

As for Exposure Compensation, on Canon cameras there is a separate Flash Exposure Compensation (FEC) that is set independently from Exposure Compensation (EC). The system will calculate the ambient exposure based on your EC setting, then fire a pre-flash to meter the flash exposure and then calculate the flash output based on the reflected flash reading plus or minus your FEC setting. Using FEC gives me control over the amount of flash, even in ETTL mode.



Jun 05, 2014 at 05:04 PM
wilt
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p.1 #5 · p.1 #5 · E-TTl 2 Exposure Compensation


What Flash Exposure Compensation does is simply 'offset' the meter results of reading the preflash. Flash Exposure Compensation simply tells the flash "give me more/less light than you would ordinarily give"...so it affects flash output, and has zero effect on shutter speed or aperture.

INDEPENDENTLY, ordinary Exposure Compensation affects only AMBIENT light gathering, with ZERO effect on flash output. The neter reads and sets exposure parameters (shutter, aperture, or both) first, before the preflash happens. And while one might think the camera 'knows' that 'flash is turned on' and changes things to suit, about the only thing that is automatic about knowing 'flash is turned on' is that the camera (when in P or Av or Tv mode) is that it alters the shutter speed to X-sync speed (and might or might not alter aperture).



Jun 06, 2014 at 02:03 PM





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