flash question

Flying giraffe

Flying giraffe

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Neil
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probably a silly question, and a mate at work who is on here too was also wondering, why is it if i take a photo with the flash off does the camera take a quick pic with a high iso, but if i flip the on board flash up does it expose for longer, ive just tried it, and without it was 1/20 with 64000, with it was 0.5" iso400, just seems strange
go on, make me look silly :lol:
 
full auto mode works fine, although it struggle to focus, something it didnt do on av, wierd
 
but i would of thought if it was doing that, the exposure would be quicker, because it knows the flash is coming
 
I'm going to guess that in Av/Tv mode, the flash is only used to "fill in" therefore it'll try and allow as much ambient light in and use the flash to top it up.

In full auto it will try and use the flash as the primary light source.

As for the ISO.... again, at a guess it will try and use the lowest ISO possible in any given situation
 
I think this will also apply to your 550D.. there's a menu option for flash in Av mode that you can set. Out-of-the-box the camera is set for vary the shutter speed as it sees fit to match the selected aperture. If you change the option you can set the shutter speed for flash using Av to the max synch speed (1/250). Doing this will make the cameras behaviour much easier to predict and make it easier to take control of the end result.

The various auto modes work in different ways (e.g. auto ISO may or may not use the full available ISO range of the camera depending on the model). To use auto modes effectively you really need to read the manual and learn how they work and what they are trying to achieve (in general they are looking for a hand-holdable shutter speed and will sacrifice whatever other settings are available to do this). Sometimes it's just easier to learn to use Av, Tv and Manual - the result of using auto modes can be far too difficult to predict!
 
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