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Archive 2016 · Strange phenomenon Auto ISO

  
 
Chris Schlaf
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p.1 #1 · p.1 #1 · Strange phenomenon Auto ISO


Ive being doing this for about 15 years and never came across this. Also never tried it

Both 7D11 and 1Dx when in manual mode and using and a flash (Canon 600rt) the iso is set to auto and for strange reason the iso locks at 400.
Any ideas ?

Thanks

Chris



May 09, 2016 at 07:03 PM
Monito
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p.1 #2 · p.1 #2 · Strange phenomenon Auto ISO


Auto ISO and flash are a logical impossibility. Hence Auto ISO switches off automatically (locks into ISO 400).

The reason is that once the aperture and shutter speed are chosen, then the flash system determines the exposure from the light coming in and quenches the flash when full exposure is reached. Hence the camera can't determine exposure before choosing the ISO.

Flash is metered during exposure and non-flash is metered just before exposure.



May 09, 2016 at 07:09 PM
RSHPhotography
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p.1 #3 · p.1 #3 · Strange phenomenon Auto ISO


Monito wrote:
Auto ISO and flash are a logical impossibility. Hence Auto ISO switches off automatically (locks into ISO 400).

The reason is that once the aperture and shutter speed are chosen, then the flash system determines the exposure from the light coming in and quenches the flash when full exposure is reached. Hence the camera can't determine exposure before choosing the ISO.

Flash is metered during exposure and non-flash is metered just before exposure.


This must be a Canon only thing. On Nikons you can set the Auto iso limit to whatever you want. So if you have it on Auto ISO at say 1600 and want more ambient light, then flash will only compensate when more than 1600 iso is needed to meter accurately.

I remember this drove me nuts on my 5D2. Because there is no auto ISO in manual mode on that camera and auto iso worked weirdly on AV mode.




May 09, 2016 at 11:35 PM
TrojanHorse
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p.1 #4 · p.1 #4 · Strange phenomenon Auto ISO


I haven't had a nikon in a while but it always seemed to me that the fill flash just worked better. I have to manage it a lot more on my canons. Oh well.


May 10, 2016 at 12:58 AM
dhphoto
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p.1 #5 · p.1 #5 · Strange phenomenon Auto ISO


Canons have always done this, the answer is just to set your own ISO. Canon flash works brilliantly but takes some learning.


May 10, 2016 at 01:01 AM
Monito
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p.1 #6 · p.1 #6 · Strange phenomenon Auto ISO


RSHPhotography wrote:
This must be a Canon only thing. On Nikons you can set the Auto iso limit to whatever you want. So if you have it on Auto ISO at say 1600 and want more ambient light, then flash will only compensate when more than 1600 iso is needed to meter accurately.


Hmmm, that could be a useful refinement. Ambient Auto ISO locking at the upper limit with flash kicking in when needed.



May 10, 2016 at 01:06 AM
DaveyD
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p.1 #7 · p.1 #7 · Strange phenomenon Auto ISO


I always prefer to set my own ISO.
I think canon locks it at 400 unless you use bounce, then it will change.



May 10, 2016 at 08:11 AM
diverhank
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p.1 #8 · p.1 #8 · Strange phenomenon Auto ISO


Canon will set it to ISO 400 whenever you have the flash turned on and ISO was set to Auto...but you can set the ISO to anything after that.

I find that for Canon the flash works best if you set the camera to Manual mode (controlling all 3 Av, Tv and ISO) with the flash to ETTL.

I prefer mixing ambient light with flash light so I normally set Av/Tv/ISO to ambient - 1 stop and let the flash ETTL to fill in the rest.

Keep in mind that with flash, changing Av and ISO will affect both flash light and ambient light but changing Tv will only affect ambient light because the flash duration is so short.



May 10, 2016 at 01:42 PM
RSHPhotography
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p.1 #9 · p.1 #9 · Strange phenomenon Auto ISO


Monito wrote:
Hmmm, that could be a useful refinement. Ambient Auto ISO locking at the upper limit with flash kicking in when needed.


Also, on the Pro Nikon bodies (I only own pro bodies) you can set your Fn or DoF button to switch flash off. This is highly useful when you have the camera on Auto ISO but set flash ISO to 1600, snap a few shots with the flash on, and then turn off flash with a button press and let auto ISO work while your flash is still on, but not firing. Comes in handy for events and sudden light change.





May 10, 2016 at 04:15 PM
ShutterbugJ
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p.1 #10 · p.1 #10 · Strange phenomenon Auto ISO


RSHPhotography wrote:
Also, on the Pro Nikon bodies (I only own pro bodies) you can set your Fn or DoF button to switch flash off. This is highly useful when you have the camera on Auto ISO but set flash ISO to 1600, snap a few shots with the flash on, and then turn off flash with a button press and let auto ISO work while your flash is still on, but not firing. Comes in handy for events and sudden light change.



Oh, I'm jealous of that. On my Canons the only option is quickly cycling the flash off and on while trying to shoot.



May 11, 2016 at 12:11 AM





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