430EX and EOS300D

[Bunglin]

Hi

I have just bought a 430EX flash unit for my Canon EOS 300D and have a question regarding the flash power when using ETTL.

If I put the camera in AV mode and set the aperture value to 8.0 (using an 18-55mm zoom lens - camera at ISO 100). I fired a few handheld test shots in doors with the lights on and am getting sutter speeds around 0.5 seconds - which result in blury photos - exposure looks ok though.

Now if I set the flash into manual mode 1/1 - the camera goes striaght to a shutter speed of 1/200th second and a shot of the same area of the room is massively over exposed.

The ETTL metering seems to be massively underusing the available power that the flash is capable of generating - instead forcing longer exposure times. I can up the exposure compensation of the flash +3 stops, however this still doesnt seem to be anywhere near full power.

Is there a way to force the flash to use a more powerful flash when in ETTL mode?

Thanks

[PacAce]

The very slow shutter speed selected by the camera has nothing to do with the flash. The reason you are getting a very slow shutter speed is because you have the camera in Av mode and the camera has determined that a very slow shutter speed is what is needed to properly expose the scene using the aperture you have specified. The camera does NOT take into account that you have a flash mounted.

If you do not want a very low shutter speed to be selected when in a dimly lit room, you can either shoot with the camera in P mode in which case the slowest shutter speed selected will be 1/60. Or, you can set the camera to Manual mode and select whatever shutter speed you want to use up to the max sync speed. If you turn on high speed sync on the flash, you'll be able to select shutter speeds faster than the max sync speed of the camera.

With the flash in ETTL mode, the camera will determine the right amount of flash to emit so that the scene is what the camera thinks is properly lit. You can use FEC (flash exposure compensation) (not to be confused with EC) to increase or decrease the amount of flash light selected by the camera.

[Bunglin]

The camera does NOT take into account that you have a flash mounted.

Not sure I understand this. I have just run a couple of test shots.

Camera 18-55mm lens set to 18mm, AV = 8.0, Iso = 100, Low light conditions, target ~3ft from lens. Flash set to ETTL mode.

Shot 1 - Metered the camera with the flash mounted but switched off - exposure time displayed in viewfinder = 6" (i.e. 6 seconds) - flash icon was not displayed.

Shot2 - Metered the camera with the flash mounted and switched on - exposure time displayed in viewfinder = 2.5" (i.e. 2.5 seconds) and the flash icon was on.

The camera does appear to know that there is a flash mounted and does adjust the exposure time to compensate for the flash - however the flash is only using a very small proportion of its maximum available power when in ETTL mode because if I set the flash to manual 1/1 - it massively over exposes.

Is the camera assuming that the flash unit attached is the inbuilt flash - because if I detach the 430EX and use the inbuilt flash - the exposure time displayed when I meter is about the same (i.e. ~2.5")

[PacAce]

Yes, you are correct in that the camera does know about the flash being mounted and that it does, in fact, account for the flash when it is turned on (my first post was a little too generalized and not properly worded). However, the exposure that is determined by the camera when setting the shutter speed is for the ambient lighting and not the flash lighting. When the camera senses that the flash has been turned on, it does decrease the ambient exposure by a stop, give or take (depending on the level of ambient lighting), as you noted, (this is known as NEVEC--negative evaluative exposure compensation) and this is being done to ensure that the picture does not come out overexposed when the picture is exposed for both the ambient lighting and the flash lighting. But the shutter speed setting, never-the-less, is set for the ambient lighting and not the flash lighting.

The camera determines the flash exposure independently of the ambient lighting and adjusts the flash power output level for the proper flash exposure for the ISO and aperture selected. The shutter speed does not come into play here unless the flash has been set to HSS mode and the shutter speed is above the max sync speed.

I hope I was able to clarify things a little better for you this time and sorry for the confusion from the previous post.

[Bunglin]

Brilliant thanks for clarifying, makes a lot more sense now. Sorry - i'm a noob to flash photography :D