Been watching Zack Arias and have a question...

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April 2008
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...admittedly, I've only watched the first hour or so at the minute, so apologies if it's answered later, but I want to make sure I understand things before my brain gets overloaded with more info.

I get that aperture controls flash exposure... that bit is obvious when you are told. Bigger hole, more flash gets in! :D

And as far as I understand it, you'd only want to move the ISO off 100 if you couldn't get enough power from your flash, or you wanted to knock down the flash power a stop or so to save battery/recharge time.

The bit I don't get is that shutterspeed controls ambient light. Surely it is a combination of aperture, ISO, *and* shutterspeed that controls the amount of ambient?

For example... if you get your chosen exposure sorted, but your flash is at full power and you want to knock it down to quarter power you will increase the ISO two stops. However, in doing this, surely you would increase the sensitivity to ambient light too and need to put the shutterspeed up two stops faster too?

If not, then why not?

All this is confusing me a little after everything I have already learnt to expose correctly without flash.

:bang:
 
yes, it is a mix of all of those three things...

however, since you have correctly set iso and aperture for adjusting the flash 'power', the only control for ambient light is the shutter speed.

Basically, think of it this way: a flash is over in 1/10,000th of a second (or so, varies...), and the aperture and iso of your camera control what effect that has in the image. you can then choose how much ambient you want to "burn in" after that flash exposure.

Hence, on a really sunny day, to correctly expose the background etc, you might want 1/250th of a second, with the settings that you've set for correctly exposing what is lit by the flash. A dark street, and you might want 1/10th of a second.

Adjusting the aperture controls the level of both the ambient and flash, shutter speed just the ambient. It takes a while to get the hang of... sometimes you want to expose correctly for flash lit things and then adjust to get the ambient right, sometimes the other way round.

HTH...I'm pants at explaining things...
 
itsdavedotnet said:
HTH...I'm pants at explaining things...
Click to expand...

That's one better than me... I'm just pants full stop! :lol:

So I was right in my thinking?

Ambient is affected by all three usual variables of ISO, shutter and aperture. Flash is affected by ISO, Aperture, flash power, and distance.
 
yep. and also things in between the flash and the subject (brollies etc all eat some light)
 
The thing to remember is that the flash speed is far faster than your shutter speed so (leaving your flash power unchanged) the only way to control how much of the flash light gets onto the sensor is to change the aperture.
So you change this until you get the flash exposed the way you want it...

...now your aperture is set and the only thing you can change is the shutter speed to control how much of the ambient light reaches the sensor.
 
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