Confused by camera behaviour

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Hi, I am new here and not sure if this is the correct place to post this question....

I have a Canon EOS 550D. I have been learning photography since about last October and so far really enjoying it! My main area of photography I enjoy is motorsport, capturing the movement etc.

Although I normally shoot in TV I was experimenting with the camera last night and noticed there seems to be a difference between auto and AV (keep reading, not quite the silly statement it might first sound!)

Basically, in full auto when focusing on a set position (inside with stable lighting) the camera will default to....
ISO 400
5.6
shutter 1/60sec
flash fired

When I switch to AV and set everything the same I get the following settings...
ISO 400
5.6
1/4sec
flash fired

The question is, why when all variables are the same (ISO, flash, focus point, lighting and aperture) does the shutter speed selected by the camera vary between full auto and TV. Surely the overal output should be the shouldnt it or am I missing something?? The full auto image comes out looking good. The AV is a touch over exposed. Also when I change to full manual and select the full auto settings the image comes out the same as full manual but the incamera light meter is at the bottom of the scale! Is this normal for the 550d?

Thanks in advance for any reply to explain why the camera behaves this way.
 
First of all which method dose the camera use to meter in Auto ie spot, center waighted, average. Depending on method it could be picking up a particularly bright or dark spot in the scine.
 
Thanks for the replies. The metering is the same. I checked that one as I wanted to keep the "experiement" controlled.

The explanation about the ambient light and fill in could explain it.

I`m not used to flash photography, normally I do motorsport work with lower shutter speeds, panning and natural light. Its only due to meeting an automotive photographer the other day that uses flashlights and static shots it got me thinking about trying to understand more about flash photography.
 
Mark is are absolutely right.

In auto, the camera relies upon the flash to expose the image correctly. Hence 1/60th regardless of the ambient light levels.

in AV the camera sets the exposure for the ambient light, then fires the flash for fill flash only.
 
That's odd, I have never had the flash auto fire when using AV mode, maybe the op has set a custom setting without realising, I pretty certain the flash should not auto trigger in any semi-manual mode??
 
I manually set the flash to fire in AV mode. I was trying to recreate the image the camera took in full auto. Like for like. All part of learning the camera and how it functions for us newbies :)

Thedodo said:
That's odd, I have never had the flash auto fire when using AV mode, maybe the op has set a custom setting without realising, I pretty certain the flash should not auto trigger in any semi-manual mode??
Click to expand...
 
RichardtheSane said:
Mark is are absolutely right.

In auto, the camera relies upon the flash to expose the image correctly. Hence 1/60th regardless of the ambient light levels.

in AV the camera sets the exposure for the ambient light, then fires the flash for fill flash only.
Click to expand...

This is exactly what's going on.
 
See handbook. There are three shutter speed options when using flash in Av mode.

Default, camera will match shutter speed to ambient and can run anywhere between max x-sync 1/200sec and 30 seconds. It will also run above x-sync with a gun that has high speed sync enabled. Or you can set it so shutter speed is locked at max x-sync speed, ie 1/200sec. Or there's a third option where the shutter speed will drop to 1/60sec to match ambient, but no longer, to prevent movement blur (but the background may go dark). This last option is also automatically selected in some other exposure modes, like P.
 
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