Confused about Speedlights

Hey guys,

This is going to be a really dumb question but I am really confused how exposure occurs when using a speedlight... relative to what the ISO / Aperture / Shutter Speed are set at on the camera.

Let me see if I can explain how I am confused.

Let's assume that I have set my camera on manual with a speedlight attached to it which is set at E- TTL. I am in manual mode on my camera and I set aperture at f/5.6. I set ISO at 200. I set a shutter speed of 1/200 (with 1/250 being the maximum I can shoot at on my Canon 7D with a speedlight). My in camera light meter is in the middle indicating I have proper exposure. I am using the speedlight as a fill flash to get rid of the harsh shadows.

Now for the confusion. If I am metered correctly at this point, per the camera.... what will the flash do? I mean, conceptually I don't need a flash to get proper exposure, correct? Will the fact I have a flash on my camera make it fire "no matter what"... with the flash actually adjusting the shutter speed (from 200) to compensate for flash being introduced, even after my manual camera settings are in place. If that is the case... then I would be limited to 1/250. I would assume that flash being introduced would speed up the shutter speed and not slow it down. Hence, the adjustable range would be from 1/200 to 1/250 only.

Does what I am asking make any sense???

I would really appreciate someone en"light"ening me on this.

Thank you.

I know the answer for the Nikon system. Canon might not be the same (no BBL or FP modes?) but here goes.

As you have set the camera explicitly (shutter speed, aperture, ISO) then the camera will do exactly what you want. It will not try to adjust things.

When you add the flash it will independently meter the exposure according to the aperture and ISO that you have set (probably for the center of the image) and produce a correct exposure for the flash.

So you have a correct exposure from your manual settings + a correct exposure from the flash - uh-oh - that's twice the amount of light you need and the image will be overexposed.

It is better when doing fill-in flash to leave the camera in Program mode with BBL flash mode. The camera understands it has to take both ambient and flash into account and reduces the camera exposure to compensate for the extra light coming in from the flash. As it is in Program mode the camera is free to adjust shutter speed and aperture to suit. (If you allow FP mode you can even go over your theoretical 1/250s limit)

If you are in a situation where there is little ambient light then set the camera to Manual mode and switch the flash to "normal" mode. The camera+flash will behave as though the flash was the only source of light. (Don't forget to switch off BBL mode or the camera will try to balance the flash with the room light bulbs. Took me a while to figure that one out)