Hello everyone! I've had my D800E about a year now, and the problem I'll describe has bugged me off and on since the camera was new. I ask forgiveness if this has been addressed already.
Basically, when I use Auto ISO with the baseline ISO = 100, everything works as expected, and the ISO floats as required up to my top limit, which I've set at ISO 6400. When I attach my SB-900 and turn it on, the top limit is immediately capped at ISO 400.
I've researched this a bit and one explanation is that the D800 firmware won't let the ISO exceed +2 f-stops over the baseline ISO when a flash is attached, hence ISO 400.
My two questions for you nikonian gurus are 1) Is this explanation correct? and 2) Is there a workaround or setting to defeat this sad limitation (besides manually setting a higher ISO)?
#1. "RE: D800E Auto ISO capped at 400 w/ SB-900" In response to Reply # 0
Seattle, WA, US
To test the theory of the +2-stops limit, I would bump up the base ISO and see what happens.
As for the reason for the limit, only Nikon can tell you that. However, one of the big complaints about using auto-ISO with flash is that the (previous) cameras would always max out the ISO before firing the flash, which was the opposite of what folks wanted.
---------+---------+---------+---------+---------+ Joseph K Seattle, WA, USA
#4. "RE: D800E Auto ISO capped at 400 w/ SB-900" In response to Reply # 3
Very easy to turn Auto-ISO off temporarily - press the ISO button (its the one at the back on the top-left dial) and rotate the sub-command dial (or the main command dial depending how you have them set). Then, while still holding the ISO button, use the other dial to set the ISO you want.
#5. "RE: D800E Auto ISO capped at 400 w/ SB-900" In response to Reply # 4
LaJolla, CA, US
What kind of flash effect are you looking for? What is the max aperture of your D800 lens? What mode are you shooting in? P,A or M,S? Are you shooting in slow sync, or rear sync? What flash aperture do you want to shoot at? How far from the flash is your subject? Do you just want to shoot iTTL balanced fill flash with available room light? Many different flash questions that have different answers depending on what the user requires. If you are just shooting normal front curtain sync in P mode the maximum aperture of your camera lens will determine the upper limit of your floating ISO. Try experimenting with your D800 built in iTTL flash that has a nearly 1/3 smaller guide number than your SB-900 and your available light iTTL balanced flash results will be easier to see. good luck.
#7. "RE: D800E Auto ISO capped at 400 w/ SB-900" In response to Reply # 5
Cape Coral, US
>If you are just shooting normal front curtain >sync in P mode the maximum aperture of your camera lens will >determine the upper limit of your floating ISO.
I thought the same until I experimented and I see the same thing as the OP. There's a hard, fixed 2 stop auto-ISO increase that only seems to come in with an external flash attached (not the popup). I tried a variety of settings and some cause no increase (e.g. commander mode), but none of them would go more than 2 stops, at least that I could find.
#6. "RE: D800E Auto ISO capped at 400 w/ SB-900" In response to Reply # 0
Cape Coral, US
This is fascinating. I had not noticed that "feature". I have the D800 and SB-800, and just tried it, and see exactly as noted (and it does appear to be a 2 stop limit at least from experimenting). I read the referenced pages in the manual and didn't come away with an understanding of this feature.
It's contrary to what the built in flash does, where the auto-ISO will go up to the maximum, and worse ALWAYS goes up to the maximum before it will increase flash power output. I have always found that ridiculous, and much worse than the older cameras which FIRST increased flash output THEN increased ISO (such as the D300).
One workaround for the built in is to set it to commander mode, which effectively disables auto-ISO (the opposite of the workaround the OP wants, I realize). Since learning this I tend to always keep both flashes in commander mode in case I have auto-ISO on, as I hate suddenly going to ISO 6400 (or higher) to take a flash picture of someone 5 feet from me.
Thank you for posting this question, it's something I had not run across.
#9. "RE: D800E Auto ISO capped at 400 w/ SB-900" In response to Reply # 6
LaJolla, CA, US
Indeed an interesting firmware cap with the current d800, d4, d600 using an sb800 or sb900 - with all cam bodies set to auto iso. My guess is that this is a nikon engineering 'hangover' from the film days where indeed the max aperture of the lens determined the iso the flash would use. Remember the simple algebraic relationship from the days of exploding flash bulbs: guide number is approx equal to aperture multiplied by the flash distance to subject. With floating iso set on current Nikon DSLR's, all the possible nikon lens apertures from f1.4 to f/32 can be covered with an external flash power output floating between iso 100 and iso 400. If you want to experiment and play around with an sb800 or sb900 at a higher than iso 400 iTTL balanced fill flash, just set your camera body iso sensitivity manually to something over 400 iso