Settings on auto v program.

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giw12

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Hi All

I bought a Canon 450D recently having spent years pointing and shooting. So far not bad...read a couple of books and pencilled in a photography course starting in Jan.

Was playing around with the camera today and found an 'anomaly' that I couldn't explain, but bearing in mind my novice status that's maybe no great surprise.

So, to illustrate....I've got the camera now in Auto and I'm focussing on a ring binder in an artificially lit room. The flash pops up, camera focusses on subject and settings are f4, 1/60 and ISO 400.

If I switch to Av, set ISO to 400 and aperture to f4, pop the flash up, then I get a shutter speed of 1/8. All other setting appear to be the same (WB, metering mode etc.)

Logically I suppose I'd expect the shutter speed to be exactly the same as in auto mode but it's a lot slower.

Can anyone explain?

Many thanks

Gary
 
Using flash with little ambient light about, the shutter speed is largely irrelevant since the flash light will dominate. I expect that the camera simply selects the fastest possible synch speed to remove much chance of the ambient light being a factor in the exposure. If in doubt which is the right setting, try both (using a more predictable subject!) and see which looks better to you.
 
Nod said:
Using flash with little ambient light about, the shutter speed is largely irrelevant since the flash light will dominate. I expect that the camera simply selects the fastest possible synch speed to remove much chance of the ambient light being a factor in the exposure. If in doubt which is the right setting, try both (using a more predictable subject!) and see which looks better to you.
Click to expand...

Thanks for the reply Nod. Makes sense..sort of, but I'll figure it out!

Does that mean then when flash isn't required then you would expect settings to be the same?

Thanks.
 
In Auto, the camera has elected to use the flash for the lighting conditions present, and has set the shutter speed appropriate to using flash.

In Av mode, the camera assumes you are trying to capture an image using the ambient light and will set a shutter speed commensurate with that goal. The fact that the flash has popped up puts you in to 'take a picture using ambient light, but use a bit of fill flash' territory. That's why you are getting a slower shutter speed in Av mode compared to Auto.
 
In auto mode its defaulting to the pre programmed flash sync speed
So its exposing for the flash.

In Av mode its exposing for the ambient light, the flash is acting as fill in.
 
This particular issue is because of the way Canon programmes the Auto and P modes, compared to Av.

In Av, the camera will track the ambient light and set as long a shutter speed as necessary to balance with the flash - in this case 1/8sec.

In full auto or P, the camera attempts to do the same thing, but stops at 1/60sec. It makes the decision that it is better to let the background go dark than risk movement blur.

There are a couple of other options for flash in Av, in custom functions.
 
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