Auto ISO on or off when using flash?


May 24, 2005
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Woodlands
#1
May i know if there is any hard rules about ISO settings when using flash. I was at AFA in Suntec exhibition hall yesterday and realised that when i set ISO to Auto, picture tends to over exposed. I tried turning off auto iso and set iso to 200... the flash unit adjust -3 env for every shot i took and caused my pic to underexpose. in the end i have to resort to manually adjust my ISO and set the flash to -1 env.
 

Irvine

Senior Member
Jan 1, 2010
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#2
May i know if there is any hard rules about ISO settings when using flash. I was at AFA in Suntec exhibition hall yesterday and realised that when i set ISO to Auto, picture tends to over exposed. I tried turning off auto iso and set iso to 200... the flash unit adjust -3 env for every shot i took and caused my pic to underexpose. in the end i have to resort to manually adjust my ISO and set the flash to -1 env.
it largely depends on how much ambient light u want to capture. if u want to capture more of ambient light, u can choose to lower ur shutter speed, or open up ur aperture, or increase ur ISO or even a combination of all 3. ur flash isnt powerful enough to light up the entire area.

in the case of flash being too bright or too dim, dial in flash compensation to adjust manually. tat's wad i'll do.

i wouldnt touch auto iso either, since the results tend to be inconsistent
 

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May 24, 2005
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Woodlands
#4
Thank you for the reply. I knew how aperture, shutter and ISO worked. Im just puzzled about the -3 env that my flash unit auto compensate and made my pic underexposed
 

May 5, 2009
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#5
Thank you for the reply. I knew how aperture, shutter and ISO worked. Im just puzzled about the -3 env that my flash unit auto compensate and made my pic underexposed
how did you know the flash "auto compensate" for -3EV? was it the value that flashed for a while on the SB600 LED (i assume this flash unit from your signature) after you took the photo? if that's the one, that is a warning from flash (or camera) that your photo is underexposed for 3 stops even with flash firing at full power, meaning you need to adjust your ISO, aperture or shutter speed accordingly.
 

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Irvine

Senior Member
Jan 1, 2010
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#6
Thank you for the reply. I knew how aperture, shutter and ISO worked. Im just puzzled about the -3 env that my flash unit auto compensate and made my pic underexposed
my strongest suspicion is that the flash had already fired at its maximum output and the -3 EV it showed was the amount of underexposure caused despite firing at full output.

(reference: page 29 of sb-600 manual)
 

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Jan 5, 2009
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#7
Hi

This is the problem

Auto-ISO with Flash sometimes gives weired results that can over-expose the pictures.

You have also forgotten about Metering. If you meter a dark spot (esp spot metering), then the system assumes you require a higher ISO or stronger Flash.

I have always wanted a button where you can switch quickly between High-ISO, No Flash mode to Low ISO, Flash Mode. It is the C1, C2 preset buttons that are missing in the D700. I hate to fumble with the camera when the action is happening.
 

May 24, 2005
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Woodlands
#8
how did you know the flash "auto compensate" for -3EV? was it the value that flashed for a while on the SB600 LED (i assume this flash unit from your signature) after you took the photo? if that's the one, that is a warning from flash (or camera) that your photo is underexposed for 3 stops even with flash firing at full power, meaning you need to adjust your ISO, aperture or shutter speed accordingly.
Hi i think you had ans my doubt. Thank you many much.
 

May 24, 2005
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Woodlands
#9
Hi

You have also forgotten about Metering. If you meter a dark spot (esp spot metering), then the system assumes you require a higher ISO or stronger Flash.
I didnt really test it on Bright and dark area, i just tested on white and black surfaces, they gave me the same result.
 

sjackal

Senior Member
Jul 9, 2008
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#10
Nikon's Auto ISO behaves differently with different cameras and speedlight combination, and I suspect different firmware too.

Whats the camera you using and what speedlight? Was the speedlight angled up or firing straight?
 

Oct 1, 2011
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#11
personally for me.. i set iso and let flash auto adjust compensation with aperture fixed...

May i know if there is any hard rules about ISO settings when using flash. I was at AFA in Suntec exhibition hall yesterday and realised that when i set ISO to Auto, picture tends to over exposed. I tried turning off auto iso and set iso to 200... the flash unit adjust -3 env for every shot i took and caused my pic to underexpose. in the end i have to resort to manually adjust my ISO and set the flash to -1 env.
 

sf_kang

New Member
Nov 3, 2004
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Singapore
#12
Hi,
Flash photography is not difficult at all if you just want a " normal " shot. Set ISO to 800, f5.6, aperture priority, first curtain flash sync, TTL-BL on yr SB-XXX Speedlight, metering pattern set to matrix, and you WILL get most of yr shots of acceptable standard (except yr own composition).
But if u want shots that are more creative, natural looking, etc. then some fine adjustments may be needed.
For me, when shooting indoors w reasonable ambient light intensity, I first meter the indoor light in MANUAL mode. I set the aperture to f5.6. I set shutter speed to 1/60 sec. I then adjust the ISO manually until I get a properly exposed picture.
Then I set the Mode on my SB900 to TTL-BL (Thru The Lens Balanced Fill Flash). And because I want the flash to provide only fill light n not to overpower the ambient light, I set -0.7EV or -1.0EV on the Speedlight.
This setup has given me the HIGHEST percentage of good shots when working indoors n w flash.
Hope this helps. Fred
 

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