When aperture does NOT control flash exposure

Interesting read about Manual vs. TTL flash

Makes some really nice points.

Good points when using TTL. I like his blog as he answers lot of questions unlike other folks where it is only one way street.

Aperture always controls the flash exposure. He says himself that the flash had to pump out a lot more light to get the same effect.

Just because it is TTL doing it instead of the photographer changing the settings himself does not change the fact that the flash output had to change in order to maintain the same exposure when the aperture changed.

If aperture didn't control the flash exposure, then the flash wouldn't have needed to work so much harder.

^ true! I can tell when you stop down the aperture with the flash on ETTL, the flash bumps up the power to compensate. If the flash was in manual, then changing the aperture would change the overall exposure of the the photograph by controlling the flash exposure.

Dave

When you have an integrated flash metering system that accounts for aperture and ISO and adjusts flash output automatically, then things can get complicated.

A lot of old-school generalizations get thrown around these forums, and it can be confusing for novices trying to learn. If you are told that aperture controls flash exposure, then you go and take two shots at different apertures and they come out the same, it's not going to make sense unless someone gives you the rest of the story. That's what Neil is doing in his blog.

I think Neil is providing useful information for those learning flash, and Tiberius and Dave are either missing the point, or just being argumentative.

Tiberius47 wrote in post #9000057
Aperture always controls the flash exposure.

No, it does not: aperture affects the amount of light entering the camera; other technologies may exert priority control of the exposure, which is not simply the amount of light hitting the sensor.

Tiberius47 wrote in post #9000057
Aperture always controls the flash exposure. He says himself that the flash had to pump out a lot more light to get the same effect.

Just because it is TTL doing it instead of the photographer changing the settings himself does not change the fact that the flash output had to change in order to maintain the same exposure when the aperture changed.

If aperture didn't control the flash exposure, then the flash wouldn't have needed to work so much harder.

Replace the word "exposure" with "power" and I think this post would be much more easily digestable.

Aperture controls flash power? Set the flash at a particular power and the flash will give a certain exposure on the subject. Change the aperture and the flash will still be outputting the same amount of light, but the effect of that flash output will be changed. If you open the aperture, the effect is increased, if you close it the effect is decreased.

Tiberius47 wrote in post #9003770
Aperture controls flash power? Set the flash at a particular power and the flash will give a certain exposure on the subject. Change the aperture and the flash will still be outputting the same amount of light, but the effect of that flash output will be changed. If you open the aperture, the effect is increased, if you close it the effect is decreased.

Huh?!

If the lens was set to f/4 and the flash output 2 units of light to make for 'proper exposure', then when you set the lens to f/8, the flash has to output 8 units of light to make for the same 'proper exposure'. The camera on eTTL tells the flash to output 2 units vs 8 units, based upon how bright the light was thru the lens when the camera commanded the preflash to occur.

Only if the flash itself is on Manual and set to a specific power level, such as 1:4, would it output a constant amount of light regardless of the lens aperture setting.

That's my point. If it was on manual, you would need to correct the flash output for a change in aperture. In TTL, the same thing must happen. The only difference is that the camera/flash does it instead of the photographer.

If the aperture changes, flash output MUST change as well in order to compensate. Whether everything is in manual or TTL makes no difference. Aperture is still affecting flash exposure in TTL. Just because you don't need to correct for it doesn't mean it isn't happening.