ISO and Flash...

edryn80

edryn80

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Edryn
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I was at a wedding on Saturday as a guest, very hot and very pleasant day.

Getting to grips with my camera now and seeing improvements which is nice. As the sun went down, I took some first dace shots, no flash (didnt want them papped during their special moment) hence upped the ISO to 1000 to get the shutter speed I was after. I then realised I was drunk and put the camera away to get on with some dancing.

If I took some shots with the onboard flash, should I reduce the ISO back to 100? Just wondering what the camera is doing, whether it adjusts the flash strength to suit the ISO etc. and what people do when shooting in low light with flash.
 
Yes, assuming you are using a dedicated or onboard flash, the camera will make all the adjustments for you - the lower the ISO (e.g. ISO 100) the longer the flash will take to recharge as it's working harder to compensate.
 
The flash is limited by it's guide rating which defines how far away it can illuminate a subject where as the upping the ISO will brighten everything including ambient light. It's a matter of trying to balance the ISO with fill in flash.

So say I have a subject in the foreground in a dark room and I light the subject with flash and the background is pitch black I'd up the ISO to include more ambient light and down the flash power to compensate. It depends on the effect of what you want to do but most of the time you'll find ISO 100-200 (400 as a max if you're desperate for light) is the range you'll be shooting in with flash in a dark room.

Hope that helps :)
 
Your max sync speed will be something like 1/250 of a second - at 1000 ISO it is likely that 1/250 is too slow to use with flash so you'll get over exposed pics.

So yes, reduce the ISO (or use auto ISO like most sensible people :D).
 
Nawty said:
Your max sync speed will be something like 1/250 of a second - at 1000 ISO it is likely that 1/250 is too slow to use with flash so you'll get over exposed pics.

So yes, reduce the ISO (or use auto ISO like most sensible people :D).
Click to expand...

When using the on-board flash, the camera won't let the shutter speed rise above 1/250sec.

iTTL will automatically adjust to the situation, as best it can. There is never any problem reducing the flash output to the required level, but pop-up flashes don't have much power and will quickly run out of range in a large room.

In which case, raising the ISO might be necessary, and/or reducing the f/number. It doesn't increase the power of the flash, but it dramatically reduces the amount of light you need for correct exposure.
 
Many thanks for your replies, I shall experiment later. I like the idea of lighting the bits the flash can't reach with an ISO boost while using the flash for fill on close subjects.

Auto-ISO, I shall leave that for another day/do some searches!
 
Thanks Nigel, that does make interesting reading.

I guess evaluative metering is required when using the flash to automatically fill so that the camera knows about the foreground and background, then fine tune with the Flash Exposure Compensation...?
 
When possible I try to shoot and make my changes in manual, if I'm in more of a hurry I tend to shoot in TV and end up getting my aperture automatically set for me. Sometimes the aperture is not as open as I would like so I knock the ISO down a touch to widen the aperture. Leaving my shutter speed in the region of 1/200-250.

Is that a bad practice or a decent way of getting my results?

Should mention thats with a speedlite.
 
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