Balancing flash and ambient with speedlight

ChrisHeathcote

ChrisHeathcote

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Hi all another basic question but for some reason I can't get my head round this. I know its me being thick but could someone help me with this.

I understand the principle behind "dragging the shutter" and the amount of time the flash is lit for is actually a fraction of time the shutter is open. I also understand the theory behind, the shutter controls the ambient whilst aperture controls the flash. What I am struggling with is that surely by using the aperture to decrease the strength of the flash, ie make it smaller. You also result in underexposing the background. Can somebody clarify this for please, as I really want to learn to use speedlights effectively.
 
Have a gander at this video:

 
Shutter speed only controls the ambient (except if you go above the sync speed of your camera).
Flash power and distance (between flash and subject) only control the flash exposure.
Aperture and ISO control both.

If you can't reduce the power of your flash and can't move it further away from the subject (or don't want to for creative reasons) then you would make the aperture smaller (or reduce the ISO setting) as you say. You would then balance this out by decreasing the shutter speed by the same amount because the shutter speed change would only affect the ambient.
If you went from f/5.6 to f/8 or from ISO 800 to ISO 400 that's one stop darker so you would adjust your shutter speed one stop brighter to compensate, e.g. from 1/250 to 1/125.
 
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ChrisHeathcote said:
Hi all another basic question but for some reason I can't get my head round this. I know its me being thick but could someone help me with this.

I understand the principle behind "dragging the shutter" and the amount of time the flash is lit for is actually a fraction of time the shutter is open. I also understand the theory behind, the shutter controls the ambient whilst aperture controls the flash. What I am struggling with is that surely by using the aperture to decrease the strength of the flash, ie make it smaller. You also result in underexposing the background. Can somebody clarify this for please, as I really want to learn to use speedlights effectively.
Click to expand...

This may be your problem. While this is often said, it's not true. The only true bit is that shutter speed does not affect flash exposure. See Darren's reply.
 
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Thanks for the comments everyone. I was certain my logic was right but as you rightly point out, so many "experts" quote the line, he even says it in the video.

So to clarify, to balance correctly meter for the background , BOTH shutter and aperture, then adjust flash power, either manual or using FEC (canon) to adjust flash exposure.

If the flash is lighting the background then either move subject further away from the background or the flash closer to subject (inverse square?)
 
ChrisHeathcote said:
Thanks for the comments everyone. I was certain my logic was right but as you rightly point out, so many "experts" quote the line, he even says it in the video.

So to clarify, to balance correctly meter for the background , BOTH shutter and aperture, then adjust flash power, either manual or using FEC (canon) to adjust flash exposure.

If the flash is lighting the background then either move subject further away from the background or the flash closer to subject (inverse square?)
Click to expand...

Everything depends on the ambient light level. Regardless of what you're trying to achieve, that is always the starting point and everything hangs around it.

A good starting set-up is to adjust the camera and flash so there's lee-way up and down on everything, if possible. Basically, mid-range settings. For example, don't set the shutter speed to max x-sync as that means you can only go slower; don't put the flash on full power until you have to; use a mid-ish ISO settings so you can adjust that either way, same with aperture.

Of course that's not always possible, or you might have already decided you need a certain aperture for depth-of-field. But there's usually a bit of give in one or two settings and that will make things easier and more flexible.
 
Generally I describe it like this - shutter speed AND aperture controls ambient, aperture controls flash power. Whoever came up with the 'theory' quoted by the OP was a bit thick IMO. And ironically people still spout it as if it's correct. :banghead:
 
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ryanyboy said:
Generally I describe it like this - shutter speed AND aperture controls ambient, aperture controls flash power. Whoever came up with the 'theory' quoted by the OP was a bit thick IMO. And ironically people still spout it as if it's correct. :banghead:
Click to expand...

And ISO?

The simplest truth is that shutter speed does not affect flash exposure. All controls (shutter speed, aperture, ISO) affect ambient.
 
Most decent flashes can also control their out put in manual. which gives another set of possibilities.
 
ryanyboy said:
Generally I describe it like this - shutter speed controls ambient, aperture controls flash power AND ambient. Whoever came up with the 'theory' quoted by the OP was a bit thick IMO. And ironically people still spout it as if it's correct. :banghead:
Click to expand...
HoppyUK said:
And ISO?

The simplest truth is that shutter speed does not affect flash exposure. All controls (shutter speed, aperture, ISO) affect ambient.
Click to expand...

ISO? Whassat?
 
Thanks everyone, it's good to know I wasn't ring completely clueless :). I will now be practising set ambient using all settings. Possibly under exposing slightly, to allow for the extra from the flash. Flash set to manual and adjust power accordingly.

As always you have all been a great help
 
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