Canon 400d Exposure time question

[hepburn]

Hi. As some here may be aware I've been a little concerned my 400d is producing soft images. I've done a bit more testing and it's only in manual mode i seem to get soft images. Preset modes are quite sharp. So tonight I'm playing around with the camera and slap on another lens and focus on the lounge with flash enabled. So, from the same view point, focusing on same spot...

In modes P, TV, M i can get a consistent readout of f/3.5, iso100, 1/60. Fair enough, i would expect that. It's also what full auto mode wanted to shoot at. BUT in AV mode the exposure time leaps to 1.6 seconds for the same aperture and iso settings. So what gives? Does AV mode ignore the flash? Or is something amiss here?

Interestingly, when I repeat the process but with sufficient light to avoid using the flash all manual modes read the same settings, which is what I would expect.

Can anyone enlighten me?

 

[Canon Bob]

Jon,

In AV mode the camera will calculate the correct exposure without flash and then fire the flash as a fill in flash. I believe that this is true for most DSLR's and not just Canon bodies.

Bob

Edit....This is an excellent reference source for all things flash (Canon) http://photonotes.org/articles/eos-flash/

 

[RobertP]

In modes P, TV, M i can get a consistent readout of f/3.5, iso100, 1/60. Fair enough, i would expect that.

Assuming we are talking indoor flash pictures where there is not a lot of available light...

in P mode f3.5 iso100 1/60 is the camera putting the lens wide open and choosing 1/60th so there will be some exposure from available light without too much movement blur but mostly lit by the flash.

In Tv mode you told the camera to use 1/60th and want it to choose an aperture that will give a good available light exposure. The lens only opens to f3.5 so it can't do it and the display should be flashing at you. As the flash is available it uses it for light to get an exposure with the settings.

In M you decide almost everything. I say almost because the camera still works out how much flash power to push out to get a decent exposure with the settings. That means you can set f8 iso100 and 1/200th which will get you a nice sharp picture - and the flash will just punch more to get you the correct exposure.

 

[hepburn]

Guys,

Thanks for your input and especially the photonotes link. It's fascinating reading...