Flash Speed. Urgent Help

[Dom_Cabarete]

Hey guys i need some advice... I was at the skate park yesterday using off camera flash for the first time and i can seem to get the flash to fire constantly through the shot. Im using a 420 EX and a 30d. Also how do i turn the power down because peoples faces are too illuminated

Thanks again guys

 

[tdodd]

i can seem to get the flash to fire constantly through the shot

I don't understand what you mean by this phrase. Anyway, to reduce the flash power you simply dial in some -ve FEC (flash exposure compensation). That is exactly the same as dialing in -ve EC for the normal part of the exposure, except it affects the strength of the flash rather than the strength of the ambient light.

You can control FEC from either the camera or the flash itself. If the flash has an FEC set then that will override whatever you dial in from the camera.

Be aware that, your max flash sync speed is 1/250, so if your chosen combination of ISO and aperture requires a shutter speed faster than 1/250 then you will run into trouble as the camer will force the shutter speed to 1/250 and thus cause overexposure to your ambient scene.

I don't know the 420EX (I have a 580EX) but I doubt it has a high speed sync feature. If it does, then enable it and you can run with any shutter speed you like. However, for action that may actually cause more blur, because the flash will flash in minute pulses throughout the duration of the open shutter, rather than in one quick single burst.

Personally, when shooting with flash, I like to use manual exposure for my background. That fixes that side of things into place and then leaves me the creative freedom to adjust my flash power without everything else being all over the place.

 

[Janice]

I don't understand what you mean by this phrase.

I have a feeling he MAY have meant... "I can't seem to get the flash to fire constantly through the shoot

 

[Jayst84]

How are you triggering the flash? There's a good chance it doesn't support TTL, in which case you need to switch the flashgun to manual, and adjust the power either using a lightmeter or trial and error.

If you mean you're stuggling to get even exposure across the frame from the flash, check your shutter speed isn't above the sync speed of your 30D, (1/250th I think).

 

[tdodd]

I have a feeling he MAY have meant... "I can't seem to get the flash to fire constantly through the shoot

Still none the wiser Now, if that was meant to be *consistently* throughout the *shoot* then we may be getting somewhere. The things is, ETTL flash (which I'm sure the 420EX supports) is as prone to getting the exposure wrong as any other metering without flash. Stick a predominantly dark subject in front of a flash and the ETTL metering will think it needs to give a large dose of flash to bring the level up to medium grey. Stick a predominantly pale subject in front of the flash and the flash will quench early, once it has captured the tones as middle grey. I'm afraid you may need to jiggle with FEC for flash just as much as you need to jiggle with EC for non flash photography.

A classic example is the wedding couple. Shoot the groom alone and you'll need to back off the FEC. Shoot thebride alone and you'll need to dial in some +ve FEC. Shoot them both together an it will be somewhere between the two, but as the flash system likes to protect the highlights you'll probably need to go a little +ve in order not to underexpose too much.

If the distance to the subject is consistent from one shot to the next then it may be better to use manual flash so that each subject has the same illumination every time.

It would be helpful to have a complete and accurate descrition of what the problem is, perhaps with some sample images with EXIF. I'm afraid that at the moment I am having to guess at what the real problem is, which makes it pretty hard to offer solid advice..

 

[Lensflare]

You need to understand how flash works and how the shutter works.

On synch speed the shutter is open fully and the flash can fire once to expose properly. If the flah fires once when your shutter speed is too high (you probably will never see this on a new camera because overides are in place to prevent it) part of the image where the shutter curtain is still travelling blocks outthe flash and so you get part image, part blank. THAT is why there is a synch speed, it is the last chance speed where the curtain will be fully open when the flash fires.

Now, with high shutter speeds. Instead of the first curtain travelling across, a pause with it fully open, then the second curtain setting off on its jaunt closing the shutter, the two curtains start off just a little way apart and a slit travells across the frame, the width of this slit alters according to the shutter speed set. To synch with this the flash fires a burst of mini flashes, like a strobe, so that each slice of image gets a bit of flash to illuminate it.

By setting your shutter to synch speed or slower (the curtains stay open but for slightly longer each time you go down in speed a notch) you ensure that one, fast burst of flash will hit the entire image frame - or at least the ambient will.

Then set your flash according to the aperture you need to balance the shutter speed you have chosen. If you want the flash to illuminate the subject properly and the rest to be a little dark, so the "person" stands out from the background then you need to UNDEREXPOSE the ambient a touch (1 sto, 1.5 stops, maybe 2 stops on a bright day) this ensures the background and surrounding light is slightly dark, the flash lit bits of the picture will be "correct" as in they will get the full illumination from the flash provided they are in range.

Your faces being too bright are due to one of two things. Either your flash was too close for the power you had it set to, OR the combination of flash and ambient aggregated together to give overlit areas - shiny areas in an image will burn out before matt areas, because more light is reflected - that is what makes them appear shiny to our eyes.

Faces are generally shiny so they will overexpose easily, especially with direct, bright light like flash. So you simply have to adjust your flash level to suit THE FACES - then let everything else do its thing.

 

[subseasniper]

It would be interesting to see what kind of set-up he has, i.e. what type of triggers, if he has brollies or softboxes etc. We could help him out a bit more.

 

[Dom_Cabarete]

sorry guys this was a friend that signed in as me , thanks for the replies but even i dont know exactly what he meant