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Message: <blockquote data-quote="voxmagna" data-source="post: 563685" data-attributes="member: 38477">After using Auto ISO with a minimum shutter speed set I got good results for outdoor shots in A mode. I am now careful to watch what ISO is doing and modify its setting with the back wheel if I can reduce it for a slower shutter. The reason I started the thread was to explore the trade off between high ISO and more noise, and a slower shutter speed hand held with VR on. Auto ISO was working well for me once I set the minimum shutter speed and the max ISO limit. Recently it all went wrong using a Speedlight MK910 shoe flash first time. Despite trying to tell AUTO ISO what to do, once the flash fired the shot and all subsequent shots were taken at my upper ISO limit. I was using 'A' mode set for f8 or f11 and the flash had enough guide number to put the power out. The camera and TTL flash seemed to be fighting each other for supremacy with AUTO ISO shifting up to 2000+ (my limit) and flash power dropping to claim the prize! Fed up with this uncertain behaviour I fixed the ISO at 500 using the same aperture settings for more 'round the table' group shots. The camera and flash gave a decent exposure, but needed better technique on my part using bounce and diffusers to reduce foreground burnout. However, there was a tendency to under expose as I guess the flash power ran out when there was no upwards ISO compensation and aperture was fixed for the DOF I needed. However, in post I had more control over the high level foreground highlights and distant shadows using curve compensation provided I started with an  under exposed shot. This is where I think AUTO ISO wasn't working for my flash shots. AUTO ISO and flash power are linear exposure 'gain controls' affecting overall exposure according to average metering although my D750 seemed to make its own mind up to use maximum ISO after the first couple of flash shots.  Which has priority, the flash or the camera? I think the camera made the high ISO decision and the flash followed with reduced power. Without bounce or diffused flash, the near subjects faces were burned out, although the middle distance exposure was correct. Turning off AUTO ISO for shoe flash gave me results I could correct in post and still get low noise. I've been using highlight-weighted metering outdoors which works well if I do more work in post, but it seems ineffective when using shoe flash.There is an excellent thread here about using AUTO ISO with shoe flash, although I think that Nikon have changed the way AUTO ISO works with flash on newer cameras like the D750. I'm still puzzled by it for shoe flash. To avoid getting bad pictures again, I'll turn it off until I figure out what is or isn't happening.</blockquote>

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