Why isn't my camera's internal light meter adjusting for my external flash?

Question

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!

Answer 1

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.)

Answer 2

Your camera can only meter the light in the scene. The flash hasn't flashed yet, so there's no flash for the camera's meter to measure and account for.

Your camera can adjust the built-in flash automatically because it can "speak" to the flash to perform TTL (through the lens) metering. The camera tells the flash to fire a "preburst" of light at a known brightness/power level, meters the preburst, and based on the reading it gets, can adjust the power level of the flash to where it thinks a good exposure level is.

The key here is how the camera speaks to the flash. On the flash hotshoe, there are a number of contacts for the pins on the flash's foot. The one in the center of the square is the "fire" signal. The other four pins below that are how the camera communicates the preflash firing signal, different types of sync timing, and power level cutoffs, as well as adjusting settings on the flash. The Neewer TT560 only has the center sync pin on its foot. So it can't communicate anything but to fire in sync: no 2nd curtain, no TTL, no HSS, no remote control from the camera's menu. So, it can't do the TTL metering thing in concert with your camera. For that you'd need a TTL-capable flash that has all five pins on the foot.

To properly expose with this flash, you have to manually set the power level yourself on the flash's back. You can always adjust and chimp (i.e., see what you got, adjust and reshoot until you're where you want to be), do mental calculations with your flash's guide number (I.e., the guide number, divided by your aperture setting's f-number is the distance that's appropriate for your flash at a given ISO), or use an external flash meter that can measure the light from your flash and tell you what aperture setting you should use for a given ISO.

Alternatively, there are now some relatively low-cost TTL 3rd-party flashes, from makers like Neewer and Yongnuo. They're not as cheap as the manual-only models, but they're 1/2 to 1/3 the price of the OEM flashes. Just don't expect the same reliability, component quality, copy consistency, warranty service, or resale values as with the OEM units.