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flash still requires slow shutter in aV mode
In manual mode I set a shutter of 1/200 with f/5.6 using the built in flash and the image was correctly exposed (shot of work desk)..

The same scene when using aperture priority mode set at 5.6 and using the flash, the camera wants to set the shutter speed at 1/15..

I would have thought that by using the flash it would select a higher shutter speed. Can someone explain why this would happen please?.

Camera is 400D using the kit lens...

Comments (7)

The shutter speed is near irrelevant when using flash. It is the duration of the flash that is important. I imagine your cam defaullts to a shutter speed of 1/15th which can be changed..

You can use shutter speed and aperture creatively to light the background while the flash lights the foreground but that was not your question..

Chris Elliott.

*Nikon* D Eighty + Fifty - Other equipment in Profile.

Http://PlacidoD.Zenfolio.com/..

Comment #1

I don't think I can directly change the shutter speed in aperture priority mode, isn't that the point of it?..

Comment #2

I've just responded to what I think it was pretty much the same question, so I'll be short..

(answer here: http://forums.dpreview.com/...forums/read.asp?forum=1002&message=25828592 ).

RichGK wrote:.

In manual mode I set a shutter of 1/200 with f/5.6 using the built inflash and the image was correctly exposed (shot of work desk)..

Yep.

The same scene when using aperture priority mode set at 5.6 and usingthe flash, the camera wants to set the shutter speed at 1/15..

Yep.

I would have thought that by using the flash it would select a highershutter speed. Can someone explain why this would happen please?.

In Av the camera meters for the background and uses the flash to fill the foreground..

For example, if you shoot a subject which is back lit, the Av mode will metter for the background light and the flash will try to lighten your subject accordingly..

That's the way it works..

/d/n.

Camera is 400D using the kit lens...

Comment #3

Devnull wrote:.

I've just responded to what I think it was pretty much the samequestion, so I'll be short.(answer here:http://forums.dpreview.com/...forums/read.asp?forum=1002&message=25828592.

In Av the camera meters for the background and uses the flash to fillthe foreground..

For example, if you shoot a subject which is back lit, the Av modewill metter for the background light and the flash will try tolighten your subject accordingly..

That's the way it works..

Ok thanks. Why is it metering for background light in aV mode?..

Comment #4

RichGK wrote:.

Devnull wrote:.

I've just responded to what I think it was pretty much the samequestion, so I'll be short.(answer here:http://forums.dpreview.com/...forums/read.asp?forum=1002&message=25828592.

In Av the camera meters for the background and uses the flash to fillthe foreground..

For example, if you shoot a subject which is back lit, the Av modewill metter for the background light and the flash will try tolighten your subject accordingly..

That's the way it works..

Ok thanks. Why is it metering for background light in aV mode?.

Well, it's the only way, if you think about it..

You are saying to the camera: I want f5.6 AND flash. What shutter speed should it give? It could metter for the subject, but then, the flash would be pointless, isn't it? Or it could slap some preset value - and it does that in A and P mode...

Comment #5

Thanks for your help. I also just RTFM which maybe I should have done in the first place!..

Comment #6

RichGK wrote:.

Ok thanks. Why is it metering for background light in aV mode?.

In Av mode, the camera tries to correctly expose the scene, which generally means the background. The flash will basically act as a fill flash in this mode (technically, E-TTL II behaves the same in all modes, it's the mode that affects how it exposes the ambient light which determines the power output/flash duration)..

Please note that the camera has no way to tell how much flash will contribute to the exposure until the pre-flash is fired (after the shutter button is fully depressed). It has to meter the scene without regard for flash (other than in P and auto, when the camera will limit the shutter speed to 1/60 or faster when using flash)...

Comment #7

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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