Help with flash exposure needed...

Started Aug 6, 2012 | Discussions thread
Zec_
Forum MemberPosts: 51
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Re: You need to set the 380EX for High Speed Sync.
In reply to AnthonyL, Aug 7, 2012

I am not an expert (obviously :)) but in the beginning of part II of the article it says (I'm not usually using M anyway):

Unlike certain other camera systems (particularly Nikon), Canon EOS cameras always default to fill flash mode when the camera is in Tv, Av and M modes. They also perform fill flash in P mode if ambient light levels are high enough. There’s no separate switch or pushbutton to engage fill flash. For details have a look at the section on EOS flash photography confusion below...

followed by sections on fill flash ratios, and auto fill reduction:

Also called “automatic reduction of flash output” in some Canon documentation. EOS cameras automatically use regular flash exposure with no compensation when ambient light levels are low - 10 EV or lower. However, when ambient light levels are brighter - 13 EV or higher - the camera will switch to fill flash mode and reduce the flash unit’s output level. It does so in TTL mode by dropping flash output by 1.5 stops. Between 10 and 13 EV the camera will smoothly lower the flash unit’s output by half a stop for each EV.

E-TTL flash works in a similar fashion, though apparently flash output will be lowered by as many as 2 stops when ambient lighting is bright. Canon have not, however, divulged their E-TTL fill reduction algorithm. Apparently the algorithm compares the brightness level of each zone both before and after the preflash, in part to compensate for highly reflective areas.

if the camera is doing flash reduction automacically, why is it so far off?! why would my manual flash exposure comp. be needed?

ufff, this seems hard

thanks for your imput!

AnthonyL wrote:

Not fill-flash in M mode. In M mode (ETTL) the flash will consider itself to be the prime light source with ambient being provided by your settings. But correct for Tv and Av. Try taking the same sort of photo at the same settings with and without flash. You may also need to dial in some flash compensation but you may also need to consider what your camera and your flash is metering off.

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