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by Bart Arondson

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I have a Canon T3 / 1100D and I just bought a Neewer TT560 Speedlite external flash which connects to my camera's hot shoe. The camera's light meter adjusts appropriately when the internal flash is used, but it seems to completely ignore the external flash, causing my photos to be over exposed.

Is this normal, is it due to my entry-level camera and flash choice, and is there a way to make the light meter somehow know about my flash and adjust accordingly? If I can't get my light meter to recognize my flash, what are some techniques to properly expose my image? Thanks!

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Stan's correct, the flash isn't TTL, it's basically a generic one-size-fits-all flash and so can't really communicate with the camera. –  John Cavan Mar 30 '13 at 1:20

1 Answer 1

up vote 5 down vote accepted

It's not a fault of the camera, it's the nature of the flash.

While we tend to think of a camera's hot shoe as an attachment point for a flash, it's actually an accessory shoe that can accept a flash. (Other typical uses include accessory optical or wire-frame viewfinders, GPS units, video lights and shotgun microphones.) The centre, large connector terminal in a hot shoe and the outer shoe are short-circuited when the first curtain of the shutter is completely open; that's what make the shoe "hot". That circuit is dumb; the contacts are shorted when the front shutter is open regardless of whether the camera is properly set for a flash exposure, or whether or not a flash is present at all.

Manual flashes (or flashes that have their own "auto" mode) are triggered when the centre terminal and the sides of the shoe short out. They normally only have contacts at the top of the foot (the part that fits into the shoe) and at the centre terminal. They have no way of telling the camera, "hey, I'm a flash." They also have no way of knowing what the camera is doing, so your flash will happily trigger when you have the shutter set to 1/4000 even though it will do absolutely no good (only the tiniest sliver of the sensor will be exposed when the flash fires, and that tiny sliver won't be open for as long as the flash is firing if you're working at any sort of distance at all).

Flashes that use through-the-lens (TTL) metering need to be able to communicate with the camera using a more sophisticated language than a "fire right now" signal taken directly from the shutter. That's what the extra contacts on your hot shoe are for. Not only does the camera know that there's a flash attached, it can also tell it how to adjust its power output (for both the TTL metering pre-flash and the "real" exposure flash), but it can also tell it to fire at a time different from when the front curtain opens. (For instance, with high-speed sync, it tells the flash to begin pulsing when the front curtain begins to open, and in rear-curtain sync it tells the flash to fire just before the second curtain begins to close.)

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Specifically, its the nature of the particular brand and model of flash that Chuck bought. –  Pat Farrell Mar 30 '13 at 2:02
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@PatFarrell - or any other manual or auto (thyristor) flash on the market. –  user2719 Mar 30 '13 at 2:06

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