For example, if you want to shoot at 5′ with an ISO of 400, the dial lines up f/5.6 and 1/16 power. The flash has an Auto Mode, too, that defaults to f/2.8 at ISO 100. In S1 the flash will fire in response to another manual or TTL flash, while in S2 the Retro Flash will respond similarly, but ignore the initial flash.
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