Documentation on undocumented Canon flash feature (NEVEC)

Started Jan 4, 2013 | Discussions thread
Zeee Forum Pro • Posts: 24,275
Re: Documentation on undocumented Canon flash feature (NEVEC)

WilbaW wrote:

Zee Char wrote:

Foot Notes states this about AFR. It is not camera mode dependant. It is strictly baed on ambient and EV. I wish that I could disable both. I know you can disable AFR with the 1DX. Not sure about the other 1D lines. Can't with my 5D3.

NEVEC only happens with Evaluative ambient metering and AFR only with Evaluative flash metering (AFAIK), so you can avoid them both by staying away from Evaluative metering (another instance of the general principle to avoid modes in the Creative Zone which are compulsory in the Basic Zone).

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.

If you don't let things like NEVEC and AFR and the P-mode fudge mess with what you're doing, "fill flash mode" is identical to and indistinguishable from "not-fill flash mode" and "no flash mode", therefore, there is no such thing as fill flash mode, there's just independent ambient and flash metering.

Agreed. We have had these conversations before. I just posted this several days ago. First paragraph.

This kinda reminds me of diffusion. Before I took lighting courses, learning about the physics of light I thought it was something magical. Somehow some of these on flash diffusers found a way around physics and solved all shadow problems.

No insult to anyone but sometimes I think reading threads here that AFR only fills in as required for the correct exposure. However if you read Canon foot notes it just reduces flash power in ½ stops based on EV. AFR does not do anything beyond that.

Canon Foot Notes calls it Auto Fill Reduction. I would have called it Auto Flash Reduction because it does not determine correct exposure, ETTL does and AFR just reduces power in preset 1/2 stops based on a formula.

Here is a chart I posted at the link based on Canon Foot Notes and what NEVEC does that shows flash ratios based on ISO 400. AFR ad NEVEC both kick in and have a ratio of 1:1 at EV 10. AFR continues to drop ½ stop as the EV climbs. NEVEC stays at - 1 bellow an EV of 10 and under.

In conclusion I wish I could disable both.

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