Av and P mode with 420EX

[offspring]

Hi all

I am doing some test with my 10D and 420EX.

When in P mode, the AF readings are shutterspeed:60, f:2.8
But when I switch over to Av mode, the AF readings becomes shutterspeed: 0.7s, f2.8

Subject is the same.

Why????

[offspring]

anyone??????

[Falcon]

Maybe in P mode, camera sets a faster shutter speed so that user can handheld and the flash can help brighten up the scene. As for Av mode, external flash only acts as fill flash. Just a guess.

[laugh]

i believe the metering is done as if it were without a flash when used in other modes.

[StreetShooter]

Wow. You waited an entire 22 minutes before yelling for a response. Try SMS instead if you want an instant response. Or being patient. Whatever.

OK in P mode, 1/60 s is the slowest sync mode. The flash blasts out as much light as necessary to properly expose the scene (which is probably indoors, quite dim, and low ISO).

In Av and Tv mode, the camera meters for the ambient light, and the flash acts as a fill flash only.

What's the difference?

In P mode using the flash, the background appears very dark, but your subject is properly exposed. This gives you the deer-in-the-headlights appearance (similar to most P&S cameras). To reduce this, you can increase the ambient lighting, or increase the ISO.

In Av mode using the flash, the background is nicely exposed as well, and your subjects face is also nicely exposed. Only problem is that at 0.7 seconds exposure, there will inevitably be some motion blur, resulting in a "ghosting" appearance. To prevent this, either hold camera very still (eg use tripod) and ask subject not to move, or increase the ISO or ambient lighting.

By the way, those are not AF readings but exposure readings.

[offspring]

thanks for answers. anyone else?

[offspring]

Thanks guys for answers, esp streetshooter. That's why i LOVE this forum, quick and helpful answers with unoffensive sarcasm thrown in. I love you guys - now I know why some people wear clubsnap tshirts. Thought they were geeks at first, but now I'm so proud of you guys I wanna wear one too

Anyway, as SS pointed, the answer is as follows (courtesy photonotes):

That’s how EOS cameras are designed to work. P, Av, Tv and M modes all meter for flash in different ways. See the section on “EOS flash confusion” for details. Here’s the short version, which repeats some of the points made in previous FAQ questions.

Keep in mind that the camera meters for ambient (existing) light conditions and flash illumination independently.

P (program) mode keeps the shutter speed between 1/60 sec and the maximum flash sync speed your camera can handle. It does this so that you shouldn’t need a tripod, even if light levels are low. It then tries to illuminate the foreground using flash.

Av (aperture priority) and Tv (shutter speed priority) modes set the shutter speed or aperture to expose for the existing light conditions correctly. They then fill in the foreground using flash. If light levels are low you will need a tripod to avoid blur.

M (manual exposure) mode lets you set both aperture and shutter speed to be whatever you want. The camera then automatically controls the illumination of the foreground subject using flash.

[offspring]

Just read my post above, when I said I love you guys - punt intended ah.. I am not pink ah, straight guy here ok....

Better clarify just in case.....

[offspring]

Found another method in 10D is to use custome function 3.

[pethidine]

Hi there,

Someone in Clubsnap post this URL before.
I found it very useful. I'll re-post it (again):
http://photonotes.org/articles/eos-flash/

To answer ur query directly, go jump to:
http://photonotes.org/articles/eos-f...html#confusion

Hope that you will get what you want to know.

Regards