Topic: Guide Numbers and Manual Flash

[ChristopherCoy]

I posted this elsewhere, but wanted to ask here as well...

For rolls 5 and 6 of my 52 roll project I decided to try manual flash work with my Hasselblad. I've never really done it to the point that I'm fluent in its formula, so this is a perfect time to learn.

I understand that F = GN •/• Distance. So if I set my flash to manual ISO400, with a guide number of 25, then my aperture on my camera should be about f8 right? (f4 for ISO100, f5.6 for ISO200, f11 for ISO800 etc etc)

And if I am thinking correctly, this would only be for stop motion lighting right. Shutter speed would increase or decrease the ambient background lighting indoors right?

In addition, in manual mode on this flash GN 25 is the lowest setting, if I wanted to shoot at f4 instead of f8 according to the formula, my image would be two stops over exposed right? Is there a way to decrease the power further or is this where a ND filter comes into play?

This is what my flash looks like... I plan on bouncing the main head and using the sub flash for fill.

[Francois]

Actually, you shouldn't need to go through complex calculations as the computer on the back automatically indicates the proper exposure.

Be aware that in order to do fill flash, you must be careful not to exceed the camera's maximum sync speed (if the camera is a focal plane shutter only).

Flash will always freeze the action as it's faster than your shutter (that is unless the ambient light is much greater than the flash power)

The lower you set the flash's power, the faster the burst of light and recycle times will be.

When bouncing flash, you can't rely on the guide number as it will be affected by the flash to reflector distance and the surface reflectivity. Safest bet would be to use the flash in automatic mode as the device will take care of the exposure by itself.

[ChristopherCoy]

So if I set it to automatic, ISO400, and 5.6 the power will be automatically generated for the exposure? The settings show 5.0-60 feet, wouldn't my exposure be brighter if I was shooting at 5.0 feet vs say 15 feet?

[Francois]

It is, but the flash will adapt the duration to compensate for that. Your eyes won't notice it but the flash's magic eye will. I use automatic flash all the time when I use toy cameras and it's flawless. On my Nikon, I have a dedicated flash with the TTL cable so the exposure is even more precise.

[ChristopherCoy]

My dedicated flash on my Nikon is what has screwed me up. I'm used to the D7000 using TTL with my SB700's and I don't have to do any of the thinking.

Now that I'm trying to use manual flash, its a severe disadvantage because I don't have that TTL advantage.

[Francois]

Automatic flash will bring back a large part of this

[Late Developer]

As a slight "aside" when using my SB600 flash with my F5 (or D3), if I dial in -0.7 to -1.0 exposure compensation, it takes away the harshness of the flash and gives a much better "fill-in" effect. I tend to use bounce flash courtesy of a "Stofen" diffuser pointing at about 45 degrees rather than vertically at the ceiling as the ceiling may be coloured whereas the Stofen diffuser is neutral.