D4 Auto ISO with flash - SB-900, SB-700 and SB-400

Started Nov 21, 2012 | Discussions thread
jeminijoseph
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Re: D4 Auto ISO with flash - SB-900, SB-700 and SB-400
In reply to Pradipta Dutta, Dec 10, 2012

Pradipta Dutta wrote:

olyflyer wrote:

Pradipta Dutta wrote:

RickD wrote:

I could not make ISO go below or above the user-specified minimum and maximum values.

Same for me too. But it seems others were able to.

Which camera, flash and lens did you try? The D800, SB-900 and 24-120/4 definitely works, and lowers the ISO if necessary.

I tried D800 and D4 with SB900 and 24-70/2.8 Nikkor. I am not saying it does not work because both you and Jemini got the results. It is likely that the light and camera setting with which I tried, I could never get the ISO go below that set in the camera. Both cameras behaved similarly.

I set the ISO to 1000 and auto ISO on with max ISO of 6400. All the images were shot in Aperture priority at F/4. I shot our decorated Christmas Tree (the background wall is beige) from a distance of about 6 ft. I reversed the flash-head and bounced it against a fairly close wall and ceiling behind me. Net-net, there was enough potential light in the flash to make a very nice exposure at about 500 to 800 ISO. But the camera, on auto ISO, chose to shoot the scene at 2000 ISO. I repeated the test for both TTL and TTL-BL and got the exact same automatic ISO selection by the cameras.

I could have set the base ISO on the camera to a very high level (like, say 3200 or 4000 or even 5600) and proven the point. But that was not the purpose of my testing. I was trying for a more realistic situation.

Actually setting the in-camera ISO to the maximum value that you want to go (usually what ever the max ISO you set in auto ISO) is another way of using auto-ISO. The only difference is that camera works from top to bottom instead of bottom to top. This way we are allowing more ambient light in before the camera uses the flash. From my test that's what I found and that's exactly what I want. I like the natural looking photo compared to flat flash picture. The biggest disadvantage will be the white balance. Since bulb light will be much warmer than flash, you will always have mixed colors depends on which light illuminate the subject. One side of the person can be yellow and the front can be perfect color

My conclusion was that in auto ISO with flash, the cameras are bumping up the ISO to arrive at the exposure value without considering the flash and then using the flash for further illuminating the subject and balancing the overall exposure. That is not what I really want.

So you are doing it right. You should set the in camera ISO low. The difference is that camera will use more flash compared to the other way around.

When I use flash, I want auto ISO to intelligently select a low enough ISO that can be properly illuminated by the flash. In my tests, only a fraction of the overall flash power was being used.

I think we've learned some stuff...

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