Flash problems

On my old Canon 300 SLR got very good results when using my 75-300mm EF lensand old flash (compatible with canon).
Now have the 300d and 550ex flash. Very variable results when using my 300EF lens - is this because the correct info is not getting to the camera when using it on auto or P. Will I have to use it on manual only (or get a new lens ?). May be a very silly question, but I have read the manual & its no help (probably didn't understand the explanation!)

The 300D uses ETTL which doesn't use distance information from the lens. That occurs in ETTLII. The lense should not be a factor in erratic flash output. In ETTL, the flash output is biased by the active AF point which can result in widely vaying flash output if you change active AF points in an environment with lots of contrast (blacks and whites). You can get around this by switching to Manual Focus on the lens. That causes the camera to average all the focus points.
Scott

I agree, it is probably E-TTL.
Try one of the following.
1. Use Flash Exposure Lock (FEL, the * button). Before firing any shot point your camera so that the central dot on display points to something grey on your scene (not to dark and not too light). Then press * button. The flash will fire and exposure will be remembered by your camera. Recompose and make the shot right away. Don't forget to repeat this procedure before each shot. I know, it's very annoying, thanks to Canon's E-TTL
2. I remember reading somewhere, that 550EX actually allows disabling E-TTL. Read the manual for your flash and disable E-TTL. It might help.

The only way to use a 550EX and a Canon digital camera without using ETTL or ETTLII is to put the flash into Manual.
Scott

SCOTT... does the 550ex & 20d use distance?


I know the 20d does but does the 550 cripple it that much?>

550EX sets its flash zoom to the focal length of the lens, not the (x1.6) effective focal length. Therefore, its flash spread is somewhat wider than it needs to be. 580EX did that differently.

---Bob Gross---

problems with flash

Manyb thanks - replies very useful - means I can't be as lazy as I was before

The 580EX will compensate for the 1.6x magnification factor in the 10D,Digital Rebel, and 20D. Ifu use the 550EX with the before mentioned cameras you need to use it in manual to adjust for the true effective focal length of the lens.

That isn't correct. You can remain in ETTL and manually adjust the zoom of the 550EX flash by pressing the zoom button.
Scott

Actually, the first sentence is correct, but the second sentence is not.

---Bob Gross---