I don't know exactly how your particular flash works, but I'm guessing it has a built in optical slave which is picking up the camera's pre-flash and firing on that. Since you can't disable the pre-flash, that is no good.
Still think you're better off using the E-TTL cord and let the camera sort all the exposure problems.
There's a thread in the macro section with all sorts of diffuser options. One of the best is to stick a plastic milk bottle over the flash head - seriously, it works extremely well.

I have 4 different diffusers alreadybut thanks
the reason I cant use the cord is I was trying for the effect of front (built in) and side (external) lighting, to create a more natural effect rather than the side casting shadows (although I have solved that issue with a different placement).
I am using manual mode which does not produce the pre flash, the camera only fires the flash during the picture, I have tried this from 1/8 up to 1/200 on the shutter speed with it on full power (so I can see if it is registering) and still nothing.
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You cannot disable the pre-flash on a 450D's on-board unit, there is no manual control as such - only 'manual' control is to use the +/- compensation with E-TTL. The pre-flash goes out before the shutter opens so using different speeds makes no difference.
Setting the camera to manual exposure control does not set the flash to manual - you still get a pre-flash. Only way to 'effectively' disable the pre-flash is to fire it first with the * button (Flash Exposure Lock) then it will not fire again with the main exposure.

I don't know exactly how your particular flash works, but I'm guessing it has a built in optical slave which is picking up the camera's pre-flash and firing on that. Since you can't disable the pre-flash, that is no good.
hmmm now confused lol so the built in will always do a pre flash to judge the exposure level just before it will take the pic?
:bonk: I though it only done a pre flash while trying to focus in darker environments?
hmmm now confused lol so the built in will always do a pre flash to judge the exposure level just before it will take the pic?
Haha! Yes, the pre-flash confuses the heck out of everybody, but every modern camera uses the same basic auto-exposure flash system. It happens so fast you can't see it happening, hence the confusion I think. The focus-assist flash that some cameras use is different.
E-TTL works by firing a pre-measured flash pulse the moment you press the shutter release, before the mirror even starts to rise. The reflection is measured by the camera's meter, balanced against the ambient light reading, and the exposure set. Then the mirror rises, the shutter opens, the main flash fires and that's that.
With remote E-TTL flash, there's even another stage after the pre-flash when the gun sends out stream of mose-code like flashes to instruct individual remote units what power to output. It happens at incredible speed. You need a master flash controller to do that though, eg 580EXII gun.
thanks for all the advice,
I use this gun in manual 99% of the time for my macro, i've just got the bar in the pictures above to save me hand holding the light and camera together, so the triger from FITP works perfect for what I use.
thanks for all the advice much appreciated!