Help! I'm so confused!

[mrshaleyberg]

Ok, so I've been trying to master my off camera flash. I mainly mess with natural light, but I've been wanting to get the flash accomplished. I'm SO confused with how to shoot with my flash on manual. The "Determining the aperture and flash output level in the Manual Mode" is really confusing me. Is there an easier way to calculate the aperture, and to calculate the correct flash output level, and the shooting distance and all that?



This is the equation that is confusing me.

f/stop (aperture) = guide number (GN) x ISO sensitivity factor ÷Shooting distance (m/ft)

and this

Guide number (GN) = Shooting distance (m/ft) x Aperture ÷ISO sensitivity factor


I'm horrible at math, so that can't help me out any. Is there an easier way to calculate all this stuff?


Thanks!

 

[tirediron]

Not really sure why you'd want to do manual flash calculations with an SB600 and a D700, but if you insist, try using this.

 

[pgriz]

To keep things simple, keep ISO out of it, for starters. So select a basic ISO (say, 100) and stick with it.

Secondly, if you’re balancing ambient and flash, you want proper exposures for both. Aperture will be the common denominator. So, take your meter reading for ambient. Let’s say you’ve got 1/60 at f/11. Now plug 11 into the formula to get your distance at which you need to place your flash. The SB-600 has a guide number of 98 at iso 100. So, 98 divided by 11 gives you nine feet. You need to place your flash at 9 feet from your subject to have an equal amount of flash light to ambient light.

There are three gotcha’s. One, this is assuming that you’re shooting the flash at full power. Secondly, the GN of 98 is for 35mm setting on the flash. Thirdly, we are assuming you are using shutter speeds which are equal to or slower than your synch speed.

Now, say you want the flash light to be twice as bright as the ambient. That means ambient will have to be one stop under-exposed. This gives us a f/stop of 16. Divide 98 by 16 and you get 6 ft. So, you’re underexposing the ambient by one stop, and you are positioning the flash to give you a proper exposure at f/16 by moving it up to 6 feet.

If you want the flash to be half as bright as the ambient, as for fill flash, then you start with your exposure for ambient, and because the flash is supposed to half as bright, you use f/8 as the number for calculating the distance, which now is 12ft. 4 inches. That will give you a proper flash exposure at f/8 but since you’re actually using f/11, the flash exposure will appear 1 stop darker, which is what you wanted.

 

[Derrel]

Ok, so I've been trying to master my off camera flash. I mainly mess with natural light, but I've been wanting to get the flash accomplished. I'm SO confused with how to shoot with my flash on manual. The "Determining the aperture and flash output level in the Manual Mode" is really confusing me. Is there an easier way to calculate the aperture, and to calculate the correct flash output level, and the shooting distance and all that?



This is the equation that is confusing me.

f/stop (aperture) = guide number (GN) x ISO sensitivity factor ÷Shooting distance (m/ft)

and this

Guide number (GN) = Shooting distance (m/ft) x Aperture ÷ISO sensitivity factor


I'm horrible at math, so that can't help me out any. Is there an easier way to calculate all this stuff?


Thanks!

401-358 Sekonic L-358 Flash Master, Weatherproof Digital Incident & Reflected Flash and Ambient Light Meter


Flash meter. Seriously.

 

[themedicine]

Why don't you try this. Take the math out of this and try to make it more intuitive. As said, set the iso to like 100-400 somewhere in there. take a photo that makes the ambient exposure proper. if the subject is dark, so what, you're gonna fix that with with off camera flash. once you have the proper ambient exposure (making sure your shutter speed isn't more than 1/250th. if you don't know why right now, it doesn't matter, just don't do it) Now, turn on the flash and dial it in manually to make the person lit. now play!!!!

 

[mrshaleyberg]

Ok, so I've been trying to master my off camera flash. I mainly mess with natural light, but I've been wanting to get the flash accomplished. I'm SO confused with how to shoot with my flash on manual. The "Determining the aperture and flash output level in the Manual Mode" is really confusing me. Is there an easier way to calculate the aperture, and to calculate the correct flash output level, and the shooting distance and all that?



This is the equation that is confusing me.

f/stop (aperture) = guide number (GN) x ISO sensitivity factor ÷Shooting distance (m/ft)

and this

Guide number (GN) = Shooting distance (m/ft) x Aperture ÷ISO sensitivity factor


I'm horrible at math, so that can't help me out any. Is there an easier way to calculate all this stuff?


Thanks!

401-358 Sekonic L-358 Flash Master, Weatherproof Digital Incident & Reflected Flash and Ambient Light Meter


Flash meter. Seriously.

That's actually on my list to buy next! And that's the one I'm going to buy! Now...To save some money.

 

[themedicine]

You really should be able to be your own flash meter, we shoot digital for goodness sake! Can't really mess up!
Start here

 

[KmH]

Yes, you can always do trial and error. But, you may miss the shot and you'll never have that more precise knowledge that pgiz elaborated.

It is elementry school math, and many people destroy any hope of learning, by using self depreciating selfspeak (aka, an excuse) like - "I'm horrible at math", because it's only true if you repeatedly tell yourself "I'm horrible at math".

 

[mrshaleyberg]

No really, I'm horrible at math. I've been doing trial and error though. With time..

 

[KmH]

No really, you are not horrible at math.