D700 freakish ISO jump for no reason - any explanation?

Started Dec 24, 2010 | Discussions thread
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CoolHandLu
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D700 freakish ISO jump for no reason - any explanation?
Dec 24, 2010

I'm sure this is some sort of user error, but dern if I can figure it out. I was at a friend's house tonight and he asked me to snap some pics of him and his girl friend. I didn't have my flash with me and the overhead incandescent ceiling lighting was pretty much all I had. I had my fixed 50 1.8 on, and my settings were Auto ISO (min shutter 125, max ISO 3200) in Aperture mode. I was shooting pretty wide open at F2, and I had +1 EC that I had inadvertently left on from earlier that day.

Here's my first shot - the camera selected ISO 2200:

A split second later, I take the following shot - note the ISO has inexplicably dropped to 1800 (obviously, no other settings have changed - I didn't touch the rear dial to change the F stop; the only thing I did differently from the first shot is remove my thumb from the AF-On button (which is how I exclusively focus):

Again, a second or less later I take the third shot - ISO has now dropped to 1000:

Finally, my last shot - ISO is now down to 800:

These four shots were all taken in less than 3 seconds (note the time on the pics and the seconds - 56 to 58) - 4 quick clicks. I didn't change any setting, or even move much in those 3 seconds. Now that I'm home and reviewing these shots in Lightroom, I can't account for the ISO change - it's almost like I had ISO bracketing on or something.

Again, I'm sure there's an explanation here, and likely something I did. But I can't seem to "recreate" this phenomena now that I'm home - lord knows I've tried! Is this just one of those "hmmmm, never had that happen before . . . oh well" and I leave it at that? Say it ain't so Joe!
Brian

PS Could it have something to do with how the Tungsten lights were "cycling" or something?

PPS I know these shots are sucky - I was trying out various lighting in the house. So forgive the "poopy snapshot" aspect. For this post, I'm just trying to figure out how the ISO changed all by itself. Thanks!
--

I don't want to achieve immortality through my work. I want to achieve immortality
through not dying. (Woody Allen)

 CoolHandLu's gear list:CoolHandLu's gear list
Nikon D700 Nikon D300S Nikon D5100 Nikon AF-S DX Nikkor 18-55mm f/3.5-5.6G II Nikon AF-S DX Nikkor 35mm f/1.8G +18 more
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