Max f/4 Lens + TTL Flash

Started Jul 25, 2008 | Discussions thread
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Peter Kwok
Senior MemberPosts: 2,257Gear list
Pre-flash wide open, shoot after stop down
In reply to Fawad, Jul 26, 2008

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 5D Mark III Canon EOS M Canon EF 17-40mm f/4.0L USM Canon EF 24-105mm f/4L IS USM Canon EF 70-200mm f/4L IS USM +2 more
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