TTL? E-TTL? Confused!!

[Yzerwing]

I need to get a speed light for my Canon T3 but every time I try to read up on the topic my eyes glaze over and I begin to drool. Can anyone explain this stuff in english? Do I need TTL? I don't know enough about speedlights to make an informed decision.

Thank you in advance to anyone who can help subdue my confusion.

 

[lambertpix]

TTL is generic (Through The Lens), but in the context of flash control, it just means that the camera can "talk" to the flash and use its metering capabilities to set flash power, zoom, etc. E-TTL, btw, is Canon's implementation of TTL flash control, and i-TTL is Nikon's.

Whether you need it or not, you certainly don't *need* it, but with the precipitous drop in prices of third-party flash units that are capable of TTL, I'd sure recommend it. You can always turn it off when you don't need it (controlling the flash manually), but I find it really handy in settings where lighting conditions are changing rapidly and you might not have time to set flash control for each shot. TTL isn't always right, but it's usually pretty close, and it can mean the difference between getting a shot or not if you (or your subject) are in a hurry.

 

[Rick50]

Canon Flash
Canon EOS flash system - Wikipedia, the free encyclopedia

My opinion is you need it. There is a time and place for full manual flash and TTL. Take your time and do some searching before you just jump in.

Unless you have deep pockets then buy the latest from Canon - 600EX speedlites like I did. I have 2 but I also have a 5D3 camera which makes the most of that speedlite. By looking you can find cheaper alternatives.

 

[Yzerwing]

Thank you lambernpix and Rick50. I guess I was over-complicating the issue. I knew TTL stood for Through the Lens but didn't realize exactly what the benefit is from it. I guess the technical mumbo-jumbo that follows is best worked out through personal experience and experimentation..... and yes I found a less expensive 3rd party flash to go along with my inexpensive camera.

Thanks

 

[jkzo]

Try Yongnuo

 

[TCampbell]

Camera companies have gone through a variety of techniques to try to automate flash lighting.

So if you go back in time, you had a basic flash "bulb" (I'm ignoring the days of trays full of exciting explosive powders and smoke). That put out one amount of light.

After electronic speedlights were invited, one of the earlier automated systems involved a sensor on the flash that measured the return light reflected off the subject. The problem with that is that some subjects are more or less reflective than others so it was easy to get a bad exposure anyway.

TTL flash systems fired a "pre-flash" and the camera metered this low-power pre-flash to detect light. Based on the light return, it determined how much power to use for the "real flash" when the shutter is actually open.

The Canon E-TTL system meters twice and fires a pre-flash before setting the power. Here's roughly how it works...

1) It meters the scene with no flash at all. In evaluative metering mode the camera breaks up the frame into a series of tiles (zones). It meters the light for each zone.

2) It fires the flash on pre-flash power (by default this is just 1/32nd of the flash's power capability). But... (continue to next step)

3) As it fires the pre-flash... it meters the scene AGAIN.

4) It compares each zone from the no-flash metered scene to the pre-flash metered scene. It's looking for zones where the flash made little to know difference (possibly a light source in the scene... such as a lamp) and also looking for zones where the flash made an enormous difference (e.g. a reflective surface... possibly a mirror.) Either of those two would be problems because they would throw the accuracy of the flash.

5) It then takes all the remaining zones and determines how much of a light return it actually got. It uses this to decide how much power to use when it fires the while the shutter is open.

6) If the flash is mounted on the camera AND the flash is pointed directly ahead (the camera knows... there are sensors for this) THEN it takes the camera's reported lens focusing distance into account as well. The camera knows how much power should be needed to illuminate a subject at any given distance based on the f-stop value being used.

7) Finally the shutter opens, the flash fires, and the camera gets the shot.

All this happens so fast, most people only think the flash fired once. It does do an amazing out of work to try to eliminate false-readings and increase the number of "good" exposures.

Even with all of that... it's still not foolproof. It helps to learn a bit about how flash photography works and learn to control the flash manually. Learning what influences flash (position, distance, lighting modifiers, etc.) will really help ratchet up your skill. But E-TTL sure is convenient.

Also... Canon also has E-TTL II. That's just a rev'd version of E-TTL. The camera and/or flash will still typically display the words "E-TTL" even if it's really using E-TTL II.

 

[Actinia]

A nice explanation, I found it very useful. You could have mentioned that DSLRs offer a 'flash compensation' which allows you to reduce the flash power if you find it is over-exposing (and vice versa). I often need this when photographing fungi against a dark (or distant) background.

 

[Rick50]

A nice explanation, I found it very useful. You could have mentioned that DSLRs offer a 'flash compensation' which allows you to reduce the flash power if you find it is over-exposing (and vice versa). I often need this when photographing fungi against a dark (or distant) background.

I agree. I often use the flash exposure compensation to adjust after the 1st exposure. This allows me to usually get a good exposure in just 2 shots. When I use full manual flash it takes much longer (for me). I usually only use manual when on a tripod and I can use a separate light meter.