Is auto ISO fixed with fill flash?

Started 3 months ago | Questions thread
Kev The Doc Senior Member • Posts: 2,216
Re: Is auto ISO fixed with fill flash?

sybersitizen wrote:

Kev The Doc wrote:

dbm61 wrote:

Auto ISO and TTL are counter-intuitive. Auto ISO will try and boost the exposure before the flash even fires. Then TTL tries to sense the needed flash to fill in the rest. And bouncing a flash loses power. So you're using the worse possible scenario for the flash ...

I’m not sure how you’ve come to the conclusion that auto iso and TTL are counter intuitive? I’d say they work together to yield the correct exposure, but until you’re experienced and knowledgeable with flash shooting you might not always get the desired results.

If the discussion is about auto ISO in combination with TTL autoflash, Sony cameras have a pretty long history of generating some less than ideal results that way. (Maybe other brands as well, but my experience with those is limited.) I wouldn't use the term counter-intuitive, but I'd call it a less than ideal approach.

I had exactly the same problems as the OP when starting off, but now I realize I didn’t know what I was doing 😀.

Now that you know what you're doing, how do you make auto ISO with TTL autoflash produce ideal results every time? What do you do differently now?

This is a bit of a repeat of what I've already posted tbh, but the key learnings for me are:

1) Set the auto iso range wide enough so that ambient light plays a role in the exposure, understanding the camera will only go to half of the upper value. In the early days when I set this too tight and expected too much from the single flash unit I'd get inconsistent results i.e. lots of underexposed shots.

2) My bounce technique has improved to give better directional soft fill light, I think this also helps accomplish a more pleasing and consistent exposure.

3) Accept that ambient light will play a role and set your SS accordingly regarding motion.

4) Set a custom button to show "Shot Preview" to visualize ambient exposure through the EVF.

5) Use center zone exposure to ensure my subject is correctly exposed as the priority.

6) Know when to switch to manually setting iso for an additional level of control.

7) Don't be scared of using HSS when the circumstances require it, but understand it's limits in terms of flash power output degradation.

8) I have the TT350, the V860II, and the V1. Since getting the V1 I use that all the time and some people have commented that they think it gives more consistent TTL performance so could be an additional factor, but I wasn't having problems with the TT350 or V860II anyway.

Some people have reported problems when below f4 with the Sony / Godox combo, I personally haven't experienced any problems related to what F stop I'm using.

As for the original question ... One possible reason for the auto ISO algorithm to choose a lower value than the designated maximum is that the camera knows a flash will be fired during the exposure, and there will be more light than is provided by the ambient source, so the ISO won't really need to be set as high as it would without it. But a potential sticking point is that the camera can't accurately predict how much light the flash will be able to contribute until the metering flash is fired and analyzed, when the ISO has probably already been set.

The iso selected by the camera under auto iso shouldn't be based on being no more than half of the auto iso range as that auto iso range is just an arbitrary selection from the photographer based on their tolerance for things like noise and dynamic range. The camera should select the most appropriate iso within the range for the particular lighting condition. For example if I set max iso to 3200 and it uses 1600, why for the same shot should it use 3200 iso just because I change the max iso to 6400? Anyway, it is what it is and we just have to live with it, no big deal.

 Kev The Doc's gear list:Kev The Doc's gear list
DxO One Sony a7R II Sony a6500 Zeiss Loxia 21mm F2.8 Sony 1.4x Teleconverter (2016) +4 more
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