Forcing the flash in Av Mode with a T2i

[Happy_Mummy]

So I posted in photographing people about the trouble of trying to get candid shots of kids with their hat on a sunny day. Here is the link to the post if you want to read more. I put up 2 threads, one of which includes a photo example. Kid Hat photos

I know to get the child's face out of shadow my best bet would be a different hat, or adjusting the hat, or even better, shooting in shade, however with a 3 year old the moment can get completely lost by doing this! The only other option I can think of is forcing the flash. If someone could share with me how to do that with a T2i that would be appreciated, but it is something I can look up. What I really want to know is how do I compensate the aperture when using a flash? I normally shoot in Av mode as I'm finding those are the best pics, but as I haven't figured out how to force the flash, I haven't played with aperture and I'm just looking for a rough guideline or rule of thumb. Would a big number work best or smaller number? I realize that I may lose or gain depth of focus when I do this, and I'm not even sure that I need to make much adjustment to this. My logic says that I should open it up by going with a lower f-stop since that freezes action faster? But I have no idea!!! Help! Thank you in advance!

[alphavalues]

When you add light from the flash, you'll want to narrow the aperature, ie use a larger F number.

You might try setting the aperture where the AV mode puts it, then changing to manual and reducing the shutter time.

[Doug Pardee]

Don't try to carry your "Av mode" preference over to flash photography. It's a different world. With flash turned on, Av mode tells the camera "Take the picture as if it didn't have flash, and use the flash for fill." In dim light, this gives long exposures with lots of motion blur and camera shake. In bright light, the limited shutter-speed range gives overexposed photos.

The simplest thing is to use P mode with flash. The second-simplest is to use M mode with the shutter set at maybe 1/125. Remember, in a non-fill flash photo, it's the flash that determines the exposure, not the shutter speed, and the flash is always automatic (for your setup).

[inkista]

Exposure compensation in Av has nothing to do with the flash. Just use it as you normally would. If you need to adjust the flash output you do so with FEC (flash exposure compensation), which is a different, independent setting.

If you're in Av, and using the flash in eTTL II, rather than Manual mode, the camera will just basically do what you want: set the general exposure, and then pop off a little flash light as fill.

It's when you want to use the flash as your main source of illumination that you're going to run into trouble in low light situations for the reasons Doug describes above. In that situation, switch to P mode, or mess about in your custom functions if you absolutely have to stay in Av mode, and tell the flash to jack up your shutter speed to 1/200s in Av for flash.

To "force" the flash, iirc, all you have to do is pop it up. Just hit the lightning button next to the lens (p.64 of the manual), and the flash wlll pop-up and the camera will fire the flash.