How do i "preflash" if I use the * to focus?

[WildWolf]

How do I get the flash to fire before I take a picture if I am using the * to focus? Thanks in advance

[PacAce]

Unfortunately, you lose the ability to use FEL when you assign the "*" button to focusing.

[WildWolf]

what about on my 430?

[PacAce]

what about on my 430?

The EX flashes do not have an FEL button built on to it. FEL is only possible via the camera.

[canonphotog]

You shouldn't worry about this. The flash will still fire a pre-flash immediately before the main flash. You just won't be able to tell that's what it is doing.

Now that I've told you not to worry about it I should at least ask; Do you have particular reason you want FEL that would make it worthwhile going back to C.fn 4-0?

Ken

[WildWolf]

I would like a more accurate focus on some of the darker scenes I shoot, thats all.

[Jim G]

The 430EX comes with built-in focus assist beams... the red thing at the bottom on the front. If it's like the 580EX you can turn them on or off via the flash's custom functions.

Preflash is not used to assist focusing - it's for metering.

[WildWolf]

how do I get it to fire? I will have to reread the manual tonight. Thanks for the help!

[SkipD]

how do I get it to fire? I will have to reread the manual tonight. Thanks for the help!What exactly are you trying to make happen?

It sounds to me like you may not understand the functionality of the flash unit. The pre-flash is not something you can control. It is purely a function for the camera/flash unit to measure how much light is needed from the flash for an exposure.

Are you possibly referring to the focus aid instead of the pre-flash?

[WildWolf]

I am still a newbie.....that being said, I would like to be able to "prefire" the flash to get accurate focus. Sometimes, my lens hunts too much in the dark and doesn't "lock in".

[Maeglin]

Between the 20D and the 430EX, only the 20D's built-in flash "prefires" to assist auto-focus. That's because it doesn't have the autofocus assist beam that the 430 has... the red light near the base of the front of the flash.

[WildWolf]

and there is no way to use the one on the 430?

[René Damkot]

And focus assist will only work with the cameras AF set to One Shot (or AIfocus IIRC). It won't emit when on AIServo.

[SkipD]

I am still a newbie.....that being said, I would like to be able to "prefire" the flash to get accurate focus. Sometimes, my lens hunts too much in the dark and doesn't "lock in".I have the 420EX, but cannot find an on-line manual for the 430EX to compare functionality.

With my 420EX, all I have to do is turn on the flash unit and activate autofocus on my camera in the dark. What happens then is a pattern of red lines is emitted from the flash unit (from the red lens, not the flash itself) and the camera uses that pattern as an autofocus target.

I use the (Custom Function 4 = 1) setting, and have to press the * button to activate autofocus. The 420EX still works just as advertised for the focus assist pattern.

All of my EOS lenses have a max aperture of f/2.8, thus my testing might be a little biased. I can imagine that lenses with much smaller max apertures might have a little trouble seeing the focus assist pattern at a distance.

After reading the above post, I realize that I have my camera set in one-shot mode and AI servo is not turned on. That's the way I use my camera all the time, and I didn't think that different settings could disable the focus assist feature.

edit: I'd bet that if you read the manuals for your camera and for your flash unit you could find a full description of how to use the focus assist. You need to find "focus assist", though, not "pre-flash".

[canonphotog]

Now I'm glad I asked what you're reason was. The AF assist beam, unless turned off on the flash(C.fn if it has it.) or turned off on the camera (20D C.fn 5-1), will emit when the camera body thinks it needs it.

With your built-in flash, AF-assist is a short strobe of flash designed to give enough contrast on your subject for the AF sensors to function. With an EX series flash mounted, AF-assist is red light emitted in vertical and horizontal lines briefly to give the camera body something to quickly focus on.

The AF-assist on the flash will not emit if you are in AI Servo.

I don't know if C.fn 4-1,2,3 and single shot will allow the AF-assist beam to emit. If it will, it will still only emit "when necessary".

Ken

[canonphotog]

Looks like I don't type fast enough...

[PacAce]

What exactly are you trying to make happen?

It sounds to me like you may not understand the functionality of the flash unit. The pre-flash is not something you can control. It is purely a function for the camera/flash unit to measure how much light is needed from the flash for an exposure.

Are you possibly referring to the focus aid instead of the pre-flash?
It just dawned on me after reading more of the OP's post that he wasn't talking about using FEL which is fired by the "*" button when C.Fn-04 = 0, so this is a little O.T. but I'm going to mention it anyway. You can control the firing of the pre-flash, by using FEL, assuming it hasn't been disabled or one has a 10D or one of the 1D-series cameras. :)

[datchi]

With your built-in flash, AF-assist is a short strobe of flash designed to give enough contrast on your subject for the AF sensors to function. With an EX series flash mounted, AF-assist is red light emitted in vertical and horizontal lines briefly to give the camera body something to quickly focus on.

The AF-assist on the flash will not emit if you are in AI Servo.

I don't know if C.fn 4-1,2,3 and single shot will allow the AF-assist beam to emit. If it will, it will still only emit "when necessary".

Ken[/quote]

Last night I was using my 350D in low light, manual, AI Servo, and my AF-Assist was going off from time to time. I had custom function #5 set to "0-Emit". Changed it to "1 Does not emit" and it still fired occasionally. Can't get it to repeat the problem today. Weird?

[datchi]

Excuse my ignorance. I was confusing the red light emitted from the 430 EX with the actual flash itself. My AI Servo will not allow the red light to be emitted. My problem is with the actual flash itself strobing.
Atch

[René Damkot]

My problem is with the actual flash itself strobing.
Atch

Sounds like you are hitting the DoF preview button, which causes the flash to emit a 'modelling light': Strobes for about a second at 70Hz...

[bwolford]

And focus assist will only work with the cameras AF set to One Shot (or AIfocus IIRC). It won't emit when on AIServo.

I wish I had seen this Saturday night!!! Argh!!!!

[r.morales]

Thanks everyone .

[LightUser]

I have the 580ex II and even though it does a short pre-flash when firing, the * preflash for some reason gives me a more accurate reading and more pleasing results than the preflash from the flash itself when firing it to take an image.

[r.morales]

Sorry , was in Mexico last 3 weeks . So , are you saying the 580 II pre-flash makes better pic's than the built in one ?
I have the 380 and only took about 6 shots with it and don't even remember the pre-flash from it but wasn't really watching for it either .

[Reefbone]

Pretty much the only way to see the pre flash is to set a long shutter speed and use second curtain sync. The preflash and the red focus assist are different animals. I think the preflash is to assist with determining the need the flash output while the red focus assist is to obviously help focus.