Question on D7100 Auto ISO behavior for flash photography

Started Mar 30, 2013 | Questions thread
Roman Fishtein
Forum MemberPosts: 55
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Re: Here are your options (Possible new solution?)
In reply to Roman Fishtein, Apr 1, 2013

Here is the second series. By lowering the shade on window I was able to cut the light level approximately by 1 stop.

Here again the first picture (no flash) comes out underexposed (at ISO 1100), so I added exposure with +1 EV (picture #7), which caused ISO to go up to 1600 and shutter speed to drop to 1/80. As you can see, build in flash (image #8) boosts ISO but not all the way, just to 720. SB400 and SB 900 keep ISO at 400 (images #9 and #10).

From these tests my conclusion is that

1) When using built in flash, D7100 raises both ISO and flash output when light level drops.

2) With SB 400 and SB 900, D7100 tries to keep ISO at 400 and raises flash output to cope with the dropping light level.

I did a quick additional test, cutting the light level by another stop, and with SB 400 and SB 900 the ISO continues to stay at 400.

#6. No flash. 1/125, F4, ISO 1100

#7. No flash. 1/80, F4, ISO 1600, +1 EV

#8. Built-in flash. 1/125. F4, ISO 720

#9. SB 400. 1/125, F4, ISO400

#10. SB 900. 1/125, F4, ISO 400

Hope this helps,

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RF

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