Max f/4 Lens + TTL Flash

Started Jul 25, 2008 | Discussions thread
Peter Kwok
Peter Kwok Senior Member • Posts: 2,406
Pre-flash wide open, shoot after stop down

Pre-flash measurement is taken while the lens is wide open, just as you view the scene thru the VF. In fact, you can see the pre-flash in the VF. So, a f2.8 or faster lens should yield better measurement.

The actual flash occurs after the mirror flips up, the lens stops down and the shutter fully opens. Thus, shooting at f5.6 has nothing to do with pre-flash with a f2.8 lens.
Peter Kwok

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Canon EOS M Canon EOS 5DS Canon EF 70-200mm f/4L IS USM Canon EF 16-35mm F4L IS USM Canon EOS M6 +5 more
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