Metering for off-camera flash question.

[TiCoyote]

Hi folks,

I just picked up a manual flash (YN-560), a stand, and a pair of eBay triggers.

I shoot with a 50D. Is there a way to get the internal light meter in the camera to compensate for the flash? Can I fire a pre-flash and then adjust? Is there a formula to adjust the meter? Or do I just take a test shot, and then adjust based on the histogram?

Thank you.

 

[gsgary]

You can do it by trial and error but it is much easier with a handheld meter that will read flash and ambient. Just remember shutter speed controls your ambient exposure and aperture controls flash exposure

 

[TiCoyote]

This is new territory for me. How does the aperture control the flash exposure?

 

[Destin]

Because the aperature controls the amount of light let in, not how long it is let in for. How long the flash's light is let in doesn't matter because it is determined by the flash's duration which is shorter than the shutter speed as long as you stay at or under your sync speed.

 

[TiCoyote]

I see, that makes sense.

 

[Robin Usagani]

But I think you rather want to change the flash power lower than making your aperture smaller (unless you are trying to achieve dark background or something).

 

[table1349]

Something like this would make you life much easier when dealing with manual strobes.
Sekonic L-308S FLASHMATE

 

[Village Idiot]

This is new territory for me. How does the aperture control the flash exposure?

Read this when you get a chance:
Strobist: Lighting 101

Manual flashes are better used off camera rather than a TTL enabled flash, since the camera will probably be constantly moving in relation to the subject. I'm not saying you can't use a manual flash on camera, but it's not as convenient.

When using a flash, you're getting two exposures, ambient and flash. If you want to use the ambient without totally killing it, adjust your ISO, apeture and shutter speed to get the ambient exposure you want, then adjust the power on your flash to add the amount of flash exposure you want.

So if you want and underexposed ambient, get your meter to read about 2 stopd underexposed and then set your flash to properly expose your subject to make the photo more dramatic.

If you want to use your flash for fill? Expose the ambient correctly then add enough flash to balance out the flash exposure to the ambient.

 

[Big Mike]

You've got it easy...this is the digital age. You can take as many test shots as you want, and see the results right away. Try learning to do this with a film camera...

As mentioned, flash exposure is controlled by the aperture, ISO, the flash's power setting and the distance from the flash to the subject...but not the shutter speed. The reason is that the flash fires for a very short time, maybe something like 1/1000 of a second. So it doesn't matter if your shutter speed is 1/30 or 1/200...as long as the shutter is open with the flash fires.

So when figuring out your flash exposure, just put the camera in manual mode and adjust the variable until you get what you want.

Of course, just looking at the image on the LCD...or even the histogram, isn't going to be perfect. That's where a flash meter comes in.

 

[TiCoyote]

Nice, thanks guys!

 

[sam_justice]

If you're new to flash photography this is INVALUABLE and I mean INVALUABLE. It's just incredible the amount of depth it covers and you'll be shootin' like a pro after watching it.
Order The OneLight Workshop DVD - I know it's pricey but you're getting 10 years of experience in one package, to me it's worth a lot more.

 

[Destin]

Also, check out strobist.blogspot.com, he has basically an entire class on off camera flash archived on his site. It is how I learned everything I know about off camera flash.
His blog updates are always pretty good too