[FrumPilot]

I just recieved the Sigma 610 flash today and did some testing. The TTL works nicely only for certain f-stops. Once I get into the f-10 and on, the TTL does a terrible job of outputting the light!
You’re going to comment “but maybe there’s not enough power in the flash?”

After taking a few pics on f-13 and being underexposed, I put it on manual, and behold beautiflul exposure! About 3 stops more! This proves that the flash has plenty available power, but in TTL, it just doesn’t wing it!

For those who have the 610, I would appreciate trying my experiment to see if you have the same issue, or is it my flash.
It could be the camera though.

I then compared the the 610 to the Yongnuo YN560 to see the difference. The YN560 is not as powerful as the 610. If the TTL is not right I’m returning this flash and I might just get another 560 to use in tandem.
I love the power of this flash and for $150 it’s a great buy. Any suggestions in this ballpark price would be appreciated!

[L33tGreg]

I have not confirmed this, but my belief is that TTL eats flash power because of the preflash, given you a lower effective power on ttl mode. I had a Metz 50 and the same issue. Now it doesn't seem to be a problem with my Metz-58, but there is more power to start with. I try to stick with "A" model flashes as much as possible because they are consistent.

[FrumPilot]

Thanks for the response.
Interesting that I just ordered the metz 50.
I should get it today or tomorrow. The one thing I liked about the Sigma besides power, was the Auto assist light which worked beatifully!
I hope the Metz will be just as good.

I agree in theory that TTL eats more, but not in this situation, because I set the body to give +1 compensation to the flash, and it did give more. Also at 1/16th power, I got a better exposures than with some shots with TTL.
So you are correct, but that's not the problem here.
Thanks again!
Jake