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 Post subject: flash overexposed
PostPosted: Wed Jul 20, 2011 6:35 pm 
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Joined: Sun Nov 25, 2007 9:18 pm
Posts: 103
Location: East Of England UK
Hi all
playing around with the flash tonight and tried an experiment.

Put my eos 40d into manual and way overexposed the scene - then popped up the flash and clicked. I expected the flash to not fire as the scene was already overexposed and the cam / flash are ttl compatible (430exii). The flash does fire tho and not sure why.

First I thought it was just pre-flash (as I understand it used by the cam sensor to work out how much flash needed) but looking at one photo with the flash popped down, and one with it up, there is a difference and the flash is firing and contributing to the exposure.

Any ideas as to why it does this ?
thanks :)

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EOS 40D / Ixus 500 / S95, Canon 24-105 F4L, 50 F1.8, Canon EF 70-300 F4-5.6 IS, Canon 10-22 IS, Speedlite 430EX II, 580 EXII
My flickr http://www.flickr.com/photos/hairyfrog/


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 Post subject:
PostPosted: Wed Aug 03, 2011 1:45 am 
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Joined: Sun Apr 18, 2010 12:33 pm
Posts: 442
Location: St. John's, NL, Canada
When your in manual mode everything is just that - manual. If you set your camera on settings that would over expose the photo, then the photo comes out over exposed. Your camera does zero compensation, i.e. "automatic" work. Also, in manual mode, if your flash is popped up, then it will fire regardless of the scene. Again, in manual mode there is zero feedback. The camera doesn't care what it's taking a photo of or how it looks, it's going to do whatever you set things too.

p.s. don't get discouraged by this, once you learn how to use it, this is the right way to shoot :-)

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Trevor Harris

Nikon D200
SB-600
YN-560 II
YN RF 603 x 4
Tamron 17-50mm f/2.8
Nikon Series E 50mm f/1.8
Nikon AF-S 70-300mm f/4.5-5.6 VR


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 Post subject:
PostPosted: Wed Aug 03, 2011 2:18 pm 
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Joined: Sun Nov 25, 2007 9:18 pm
Posts: 103
Location: East Of England UK
Prob should have mentioned that the flash was not on manual it was on ETTL.

Anyways I think the mistake I made here was thinking of the camera exposure and flash exposure as one - when in fact they are two separate things.

So, the flash exposure would have worked out correct flash for the scene (via ETTL) regardless of what the cam was set to (shutter / aperture) and hence fired to light the scene as it sees fit. All makes sense now :)

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EOS 40D / Ixus 500 / S95, Canon 24-105 F4L, 50 F1.8, Canon EF 70-300 F4-5.6 IS, Canon 10-22 IS, Speedlite 430EX II, 580 EXII
My flickr http://www.flickr.com/photos/hairyfrog/


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 Post subject:
PostPosted: Thu Aug 04, 2011 3:49 am 
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Joined: Sun Apr 18, 2010 12:33 pm
Posts: 442
Location: St. John's, NL, Canada
Quote:
Prob should have mentioned that the flash was not on manual it was on ETTL.


This doesn't really matter in regards to your question. You asked why the flash fired even thou the photo is overexposed. My answer is still true, it fired because it was up and when your camera's exposure mode is in manual (or aperture or shutter speed priority) then the flash will fire. How bright the flash is when it does fire is a function of the flash setting (manual or ETTL). manual flash and manual exposure are two different things, as you said.

Quote:
So, the flash exposure would have worked out correct flash for the scene (via ETTL) regardless of what the cam was set to (shutter / aperture) and hence fired to light the scene as it sees fit. All makes sense now


Essentially yes, but flash works out the correct exposure for the flash exposure - which is dependant on the composition. Flash will generally only effect the foreground - so it tries to get that properly exposed.

You're getting there :-)

_________________
----------------
Trevor Harris

Nikon D200
SB-600
YN-560 II
YN RF 603 x 4
Tamron 17-50mm f/2.8
Nikon Series E 50mm f/1.8
Nikon AF-S 70-300mm f/4.5-5.6 VR


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 Post subject:
PostPosted: Tue Aug 23, 2011 2:45 am 
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Joined: Mon Dec 21, 2009 3:27 am
Posts: 916
Location: UK
If you are photographing in the dark, and/or, your ambient exposure is underexposed, then the image will usually look fine.

If I am using flash, then the ambient exposure is usually too dark most of the time in any case.

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Lenses: EFS 18-55mm IS, EF 50mm F/1.8 II

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