5D3 + flash question

Started May 5, 2012 | Discussions thread
OP Olgierd Regular Member • Posts: 397
Re: 'Reporting lenses' & Speedlite head 'Straight-ahead' orientation.

ScratchDisk wrote:

There are a lot of variables to control:

You could argue that there are four modes under ETTL II:
1) Evaluative for Flash ( not set from cam's top-plate button)
2) Average for Flash
3) FEL ie central 3% spot & lock

4) Acheived-focus-distance Dominated (under 'Evaluative for flash', pre-flash metering is not linked to the focus point in use)

I find that if moving between No 1) and 4) above, it can make up to 2 stops difference, depending on the reflectivity of the dominant surface and the distance ratio between focussed target and the background.

There are several methods of avoiding No 4 (which typically is 'on-cam' & 'straight-ahead' style);
1) Engage 'Master' or 'Wireless'

2) Move the Speedlite head (even slightly) off 'straight ahead' (therefore includes all bounce positions)
3) Use a non-distance reporting lens

Finally remember that different bodies have different numbers of segments used for pre-flash metering.
Cheers, Donald

Thanks for reply. All scenarios were with flash with diffuser mounted on camera

hot shoe. I tried all combination for evaluative and average set for flash then different modes for ambient meter (evaluative, center-weighted average, partial, spot).

Whenever evaluative is set for flash scene is always heavily underexposed. Switching flash to average and changing ambient meter modes makes scene to be lit much brighter (correct exposure).
Slightly tilting head when flash evaluative is selected, list scene properly.

I understand that with diffuser is anyway better to tilt flash head but it is a problem with a small soft box too. I'm also trying to understand why this is different than with 7d and why it seems to differ for focal lengths (used 24-70 L and 100 L for test).

I'll try later with flash off camera with small soft box and head not tilted and if this is still an issue I'll post some samples.

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