Auto iso: why does my speedlight choose ISO400 ?

If i set iso to auto and use a speedlight, it then always wants iso 400. Why is this? I assume it will allow the batteries to be saved, but when trying to ballance a subject with ambient, does it make any difference seeing that i have to stop down in order to expose for a sunny environment. In my particular case i had to choose f14 in order to expose a portrait of someone standing in direct sunlight and my flash was set to full power through an umbrella. The next shot was dialed to f10 but iso 100 and the flash still on full power, the exposure was exactly the same and seemed even better due to less noise.
Is this ISO thing for speedlights only intended for shady areas or something. Because if thats the case i can understand why is because you can use a lower flash power, but when going against the mid day sun does it make any difference?
Thanks for taking your time to read this. Any enlightment will be apreciated.

The in camera meter is for ambient light exposure. It doesn't know how much flash is going to be in the picture. With ettl, when you press the shutter button, the flash fires a preflash, which then tells your camera how much flash to add.

Like Mr. B. said, the varying the ISO adds to many variables for the camera to handle.

The real answer is that if you want to take control of the situation, such as when balancing with ambient, you really should just take control and skip the automated BS. If you want ISO 100 then set the camera to ISO 100.

Valid points, well-taken.

Still, wouldn't it be cool if the camera would adjust the ISO in the same manner as it adjusts the shutter speed in Av mode or adjusts the aperture in Tv mode?

Is that really too much to ask?

Curtis N wrote in post #13091221
Valid points, well-taken.

Still, wouldn't it be cool if the camera would adjust the ISO in the same manner as it adjusts the shutter speed in Av mode or adjusts the aperture in Tv mode?

Is that really too much to ask?

The 5D Mark II has auto ISO, and I think some of the newer Rebels, as do some Nikon bodies... though I couldn't imagine ever using it.

BrandonSi wrote in post #13091257
The 5D Mark II has auto ISO, and I think some of the newer Rebels, as do some Nikon bodies... though I couldn't imagine ever using it.

If you read the rest of the thread, you'll see that we are discussing how that auto ISO works...

krb wrote in post #13091268
If you read the rest of the thread, you'll see that we are discussing how that auto ISO works...

This entire thread is just confusing, and hurts my head..

Curtis N wrote in post #13091221
Valid points, well-taken.

Still, wouldn't it be cool if the camera would adjust the ISO in the same manner as it adjusts the shutter speed in Av mode or adjusts the aperture in Tv mode?

Is that really too much to ask?

If you think it's bad as is, you should have tried it on the 40D. It basically just used ISO 400 no matter what.

When learning flash, one needs to keep it simple. Adding Aut ISO to the equation is the last auto function I'd be adding.

Thanks. I thought as much. Seems like im going full manual everything for todays shoot

krb wrote in post #13090972
Like Mr. B. said, the varying the ISO adds to many variables for the camera to handle.

The real answer is that if you want to take control of the situation, such as when balancing with ambient, you really should just take control and skip the automated BS. If you want ISO 100 then set the camera to ISO 100.

Best advice on offer..

boerewors wrote in post #13092515
Thanks. I thought as much. Seems like im going full manual everything for todays shoot

ETTL can work wonders as long as you know it's limits.

just curious what shutter speed were you seeing as a result?
and were you using m, tv or av modi am not surprised it was holding iso400, but also what sync speed to the flash were you using?

unless i misread... full daylight with a full speedlight blast seems pretty excessive.

but iso 400 should produce zero noise that is visible in any normal prints unless you are printing lifesize

v_lestat wrote in post #13094196
full daylight with a full speedlight blast seems pretty excessive.

Not at all. In full daylight, a full power blast from the Speedlite is often necessary to compete with the sun and lift the shadow areas (depending on the distance). Since you're limited to X-sync shutter speed, you control exposure by using ISO 100 and stopping down the aperture.

Auto ISO does some very bizarre things without flash. https://photography-on-the.net …p?p=13029993&po​stcount=21 It is quite consistent in doing some oddball things with flash, too.


Even the newer models continue to do bizarre things with Auto ISO, even though they are better than the earlier, more flawed Auto ISO models.