In TTL the flash still can only use it's given power settings right?

What I mean is if you shoot in TTL the flash and camera figure out what power to shot at. Even if you shot in manual you should be able to recreate the same exposure unless it was HSS right?

TTL has no way to shoot below or above its power settings?

A flash has only its full power output, and it has the output fractional power levels...regarless if the flash is in Manual or ETTL or HSS.

• In Manual, you can 'command' the flash to a set fractional power (e.g. M/4 or quarter power) via camera controls or via flash controls.
  
• In ETTL/HSS the camera flash meter reads the light from the preflash, and the camera then commands the flash to output a suitable amount of light to render 'proper' exposure.
  

Wilt wrote in post #17919212
A flash has only its full power output, and it has the output fractional power levels...regarless if the flash is in Manual or ETTL or HSS.

• In Manual, you can 'command' the flash to a set fractional power (e.g. M/4 or quarter power) via camera controls or via flash controls.
  
• In ETTL/HSS the camera flash meter reads the light from the preflash, and the camera then commands the flash to output a suitable amount of light to render 'proper' exposure.
  

Any exposure available in ETTL/HSS is also available in Manual with one exception...flashes sometimes have a wider range of control thru ETTL/HSS than it has under M... for example, with the Canon 580EX you can get to 1/128 in Manual, but ETTL can control to 1/256.

And, likely the TTL metering will be more granulated. i.e. tighter power control than 1/3 EV.

Wilt wrote in post #17919212
Any exposure available in ETTL/HSS is also available in Manual with one exception...flashes sometimes have a wider range of control thru ETTL/HSS than it has under M... for example, with the Canon 580EX you can get to 1/128 in Manual, but ETTL can control to 1/256.

My testing showed that 1/512 was provided with the 580EX II. It is only the human control interface which is limited to 1/128.

That is the beauty of ETTL. Because there is a pre flash the system can determine the correct output before the actual flash exposure exposure. Unlike Auto where the flash fires at full power and the flash sensor determines the correct output. It has to shut down the flash tubes and account for drainage as well. I purchased a Metz 58 AF for it's legendary auto exposure which did not disappoint. I did realize later that it did not work well with high ISO and wide open apertures. It always gave me an overexposure warning so I had to revert to ETTL.

I guess going the other way would be limited. If ETTL decided to use full power and you decided it needed more, adjusting FEC to a + value would not give you more power.

digital paradise wrote in post #17926096
That is the beauty of ETTL. Because there is a pre flash the system can determine the correct output before the actual flash exposure exposure. Unlike Auto where the flash fires at full power and the flash sensor determines the correct output. It has to shut down the flash tubes and account for drainage as well. I purchased a Metz 58 AF for it's legendary auto exposure which did not disappoint. I did realize later that it did not work well with high ISO and wide open apertures. It always gave me an overexposure warning so I had to revert to ETTL.

I guess going the other way would be limited. If ETTL decided to use full power and you decided it needed more, adjusting FEC to a + value would not give you more power.

I would not say the benefit of ETTL is 'no overexposure'...if it needed 1/1024 power, it would indeed overexpose and not give you a warning until the flash confirmation light failed to attain 'proper' exposure. TTL and ETTL are both governed by the limits of the smallest fractional level it can achieve, and so is photosensor flash. Yes, 1/512 is far less than 1/128. But that is flash design, just as some studio flash have 5 stops of control while others have 7 stops of control, and the Canon 580EX has 10 stops of control under ETTL but not under Manual setting.

Wilt wrote in post #17926244
I would not say the benefit of ETTL is 'no overexposure'...if it needed 1/1024 power, it would indeed overexpose and not give you a warning until the flash confirmation light failed to attain 'proper' exposure. TTL and ETTL are both governed by the limits of the smallest fractional level it can achieve, and so is photosensor flash. Yes, 1/512 is far less than 1/128. But that is flash design, just as some studio flash have 5 stops of control while others have 7 stops of control, and the Canon 580EX has 10 stops of control under ETTL but not under Manual setting.

Good points.