Fill Flash with the 300D

[dphoto]

Hey there folks!

Is is possible to use fill flash with the 300D? If I pop the flash up when I have proper exposure, how much flash is going to be fired? Also, would I use manual mode so that my aperature and exposure time values are not changed?

Thanks,
-Deva

[slin100]

The amount of fill flash depends on the exposure value (EV) and the exposure mode. Read this section (http://photonotes.org/articles/eos-flash/index2.html#fillflash) on fill flash and auto fill reduction.

[dphoto]

Wow, thanks for the link! I think I'm beginning to get this. When using the flash, Av and Tv modes expose for the background. So if I'm using Av mode and my background is bright and my subject is dim, the camera will use a short exposure time (for the background) and fire enough flash to illuminate the subject. Is this right?

But what about the situation of a dim background and bright subject? In Av mode, this time I will get a long exposure time (for the background) and the flash will... do what? Fire a lot of flash so as to freeze the subject when the background is being exposed? But then won't the subject be overexposed? I don't understand how, in the case of a dim background, while using the flash on the camera, the background can be exposed properly without overexposing the subject. Any ideas?

Thanks,
-Deva

[Tom W]

Wow, thanks for the link! I think I'm beginning to get this. When using the flash, Av and Tv modes expose for the background. So if I'm using Av mode and my background is bright and my subject is dim, the camera will use a short exposure time (for the background) and fire enough flash to illuminate the subject. Is this right?

Very close - actually, in Av and Tv modes, the camera meters the entire scene and exposes accordingly if you are in evaluative metering mode. This includes the background and foreground. The flash then meters the main subject based on focus point and E-TTL magic. Bright background/dim subject is an ideal situation for fill flash.

But what about the situation of a dim background and bright subject? In Av mode, this time I will get a long exposure time (for the background) and the flash will... do what? Fire a lot of flash so as to freeze the subject when the background is being exposed? But then won't the subject be overexposed? I don't understand how, in the case of a dim background, while using the flash on the camera, the background can be exposed properly without overexposing the subject. Any ideas?

Thanks,
-Deva

The second part is a little harder to answer - the flash certainly won't overpower the picture (or at least it isn't supposed to), but I'm not sure how well flash duration can be relied upon to freeze action. I would think that in this case, one option would be to sync your flash at a higher speed in Tv and use it merely to fill in the shadows, while relying on fast shutter to stop action. Of course, the trade-off is a dark background.

I'm interested in hearing some input from those more experienced in this type of situation as well.

[drisley]

Interesting...

How does the flash (say 420ex) behave when you point it at the ceiling for bounce flash? Does it realize this is what is happening and adjust the output accordingly?

[maderito]

But what about the situation of a dim background and bright subject? In Av mode, this time I will get a long exposure time (for the background) and the flash will... do what? Fire a lot of flash so as to freeze the subject when the background is being exposed? But then won't the subject be overexposed? I don't understand how, in the case of a dim background, while using the flash on the camera, the background can be exposed properly without overexposing the subject. Any ideas?

Thanks,
-Deva

The second part is a little harder to answer - the flash certainly won't overpower the picture (or at least it isn't supposed to), but I'm not sure how well flash duration can be relied upon to freeze action. I would think that in this case, one option would be to sync your flash at a higher speed in Tv and use it merely to fill in the shadows, while relying on fast shutter to stop action. Of course, the trade-off is a dark background.

I'm interested in hearing some input from those more experienced in this type of situation as well.

On the 10D, you can disable automatic fill-in flash (via one of the custom functions). Then you would be able to stop action with the flash as long as you minimized captured ambient light from the subject. One way to do this would be to use manual camera exposure (not manual flash). The objective would be to expose the subject via the flash while setting aperture & shutter speed for an underexposed background. If you let in too much ambient light, you just get ghosting - a composite flash+ambient light image.

In more typical flash situations (when flash is the primary light source), I often set the 10D custom function which forces the shutter speed to 1/200 while in Av mode. With the shutter speed fixed at 1/200, I set the aperture for the desired depth of field. That's good enough to stop action for most shots, but often at the expense of dark backgrounds. The action is stopped by the shutter speed, not the flash.

Stopping action with a flash is a lot harder than you think (or I have a lot more to learn). :)

[robertwgross]

How does the flash (say 420ex) behave when you point it at the ceiling for bounce flash? Does it realize this is what is happening and adjust the output accordingly?

Each flash puts out its brief pre-flash, the camera meters on that reflection, and then sets up the final exposure settings for the main flash. So, if the flash unit is tipped upward, some of its light will be bounced onto the subject, but with somewhat reduced intensity as compared to a straight-on flash. The camera doesn't know whether the reflected intensity was a result of distance or a result of dark subject, but it doesn't care, so it just sets up the final exposure settings for the main flash.

Of course, with some cameras you can compensate that up or down.

The 300D is not one that is easily compensated.

---Bob Gross---

[drisley]

Thanks Robert. That makes sense.
I just tried a few shots and that is exactly what happens.

[dphoto]

Thanks guys!

-Deva