This is a question we get asked all the time. “I’m looking to buy my first speedlite and I don’t know whether to get TTL or Manual. What’s the difference?” If you want a full technical breakdown on TTL check out Wikipedia. I’m going to keep this in terms everyone will understand.
TTL means Through The Lens metering. When you focus your camera with that half push of the shutter, your camera is not only focusing, but its taking a reading (metering) of the scene. It is taking a measurement of how much ambient light is being returned Through The Lens to the sensor.
TTL flash uses a series or infrared flash bursts before the flash actually fires. This flash information is returned back to the camera which then adjusts the flash power accordingly to set what it thinks is a well-balanced shot.
In practice this works fairly well, but what you end up with is often less than desirable. You get flat, dull looking images with flat underexposed backgrounds. TTL doesn't really care a whole lot about the background. Its main concern is exposing the subject evenly. This is where TTL really becomes somewhat useless for most photographers.
Don’t get me wrong, some professional photographers like Joe McNally swear by TTL and have mastered every nuance of its inner workings; but is it necessary for most of us? I would argue your money is much can be better spent on other equipment.
Why? I don’t want TTL telling me what my photos should look like. I want control. I don’t think I've ever shot a portrait thinking, I want this to be as neutral and flat as possible. No, I want dramatic lighting with a shadow here and a highlight there. The problem with TTL is that it is often difficult to produce repeatable results. Every time that TTL flash sends its signal back the camera, it opens the possibility for the settings to change. Ambient light, clouds, shadows, anything can change the metering. With manual I can set the power to ¼ power and it stays on ¼ power no matter what.
TTL Flash Pros
TLL Flash Cons
Manual Flash Pros
Manual Flash Cons
Yes, occasionally. If I’m at a party taking random shots in low light, TTL is great. In that situation I don’t have time to set a manual flash every shot. I need to run and gun candid shots all night. Granted I hate these type of photos because they’re on camera, but TTL gets the job done.
If you need HSS (high speed sync) then you want TTL. Manual flash is limited by your camera’s shutter speed. Typically 1/200s or 1/250s. TTL and a compatible camera allow a way around this to shoot at speeds up to 1/8000s. If you’re just starting out HSS is not really something to worry about.
Is there really a need to stay with a Canon or Nikon flash? To be honest, no not really. The current sale price of a TTL Nikon SB-910 flash is $499. The current price of a directly comparable TTL Yongnuo YN568EX II is $235 from Strobepro. Less than half the price. Now if you don’t need TTL the Yongnuo YN 560 III with a built in radio transmitter is only $100! To put that in perspective you can by 5 flashes for the price of one. What do you think is going to be more beneficial? Why don’t you start with two Yongnuo 560III’s, and a Strobepro Speedlite Flash Umbrella Kit that includes, stands, umbrellas, adapters and the bag? You’re still only at $320 for all that.
You see where I’m going with this. We sell hundreds of Yongnuo products and they've got all the features and power that you’d expect from Nikon or Canon. Plus they’re just as reliable. This is not just for beginner photographers. Our pro customers know they rarely use TTL, so why continue to invest in it? We have lots of customers that have sold their TTL flashes, gone to Yongnuo manuals, put $2000 in their pocket and ended up with more flash’s then they started with.
Only you can decide what your needs are, but think hard about what you REALLY need.