Paul C. Buff, Inc. Technical Forum

Don't really understand the relationship between the power settings on the back of the 1600 and the "stops" on a camera, if there is one. :(
Does the slider on the 1600 just measure the strength 1/32 to full power( output of the flash ) and has nothing to do with the f- stops on the camera, or am I missing the bigger picture.
Thanks.

A "stop" is a doubling or halving the amount of light. This could be doubling or halving flash power, doubling or halving ISO, doubling or halving shutter speed, or doubling or halving the area of the aperture (this last one is not linear, as you are working in two dimensions).

SO, if at full power, your flash gives you f/8 at ISO 100, then at half power, you get f/8 at ISO 200, or f/5.6 at ISO 100. So a one stop change in flash power will result in the need of one stop change in ISO or aperture to maintain the same exposure. Note, however, when using flash, the relation ship between shutter speed and flash does not apply. Except toward the extremes, the shutter speed has no bearing on flash exposure.

There is not a direct relation ship between any given aperture and any given flash power (i.e. half power does not always equal, say, f/8). Modifier, distance, ISO and other factors will all impact this relationship. However, once established, a full stop change in one will equal a full stop change in the other.

*Also note, high ambient light will throw a monkey wrench into this equation. The above is assuming low to no ambient light.

Thanks for replying, I to a point understand about doubling, i just dont understand all you are saying.
let me give you a hypothetical shot.
I have my 1600 at half power wanting to do a waist high portrait shot with the PB large soft box. i meter the light with the light meter and it says F11, i have my camera at ISO 100 in manual, shutter is set to 100.
Since i have determined the light is to bright and i want to shoot at F8, I either pull the soft box back, or cut the power down on the 1600 and meter till i get F8 or change the aperture or shutter speed.
So what am i doing wrong?

thanks,
.............M

First, for this explanation, I am assuming you are indoors. If you are outdoors (i.e. noon sun),
then there is some alteration that need to be made.

Second, you ask what you are doing wrong. However, you only say what your problem is (f/11 but you want f/8) and what you do to correct (make a change), but you do not say what your results are, so I cannot say what went wrong.

But, if you meter f/11 at half power, and you want to use f/8, then you can

A-lower the light to 1/4 power (1/2 to 1/4 power is 1 stop less light. F/11 to f/8 is one stop difference)

B-back your lights off 40%. If it is 10 feet, 14 feet would be 1 stop less light.

C-lower your ISO, if possible. Changing from ISO 100 to ISO 50 is one change.

A change in shutter speed will not affect your flash exposure, so leave it alone.

Also, most meters offer a 1/10 stop scale. This can be expressed as a digit after an apostrophe (f/11' 2) or simply a smaller number beside the aperture reading (which I cannot duplicate) or a series of tick marks on the meter somewhere (similar to the meter in your camera). These tenth stops are very important, as it can be a big shift from the whole f stop shown.

For example, f/11' 9 is only 1/10 of a stop below f/16, or two stop more than your target of f/8.

Also, make sure you are in M mode, and set your own shutter speed, aperture and ISO. Make especially sure you are in a specific ISO (the same as your meter), as some Nikons have a tendency to be confusing in some cases by appearing in manual ISO, but actually being in auto ISO. (I do not what is being seen so that this is confusing, but I have had several questions regarding this).

Thanks for the input and your time, that helped a lot, it's just going to take a while for it all to sink in.
regards,
..................M

Try not to overthink it. You can't put your camera on a certain f-stop and then correspond it to a setting on the back of the strobe....well, you can after lots of experience knowing your strobes paired with certain modifiers, but that'll come with time. Here's where they're handy....lets say you've metered f/8 and you've been shooting some shots at f/8. Now you want a little less depth of field and you open the aperture up to 5.6. Since going from f/8 to f/5.6 is one stop, you power down the sliders on all your lights one stop to maintain proper exposure. They allow you to quickly adjust the lights as you make changes in camera to either the aperture or ISO, and give you a visual reference of how much you need to move it to match that change.

f/2.8 to 8 is three stops. If you've been shooting at 2.8 and jump to 8, you can increase the power three stops on the light and be REAL close to proper exposure. In fact, I've found it to be accurate enough for me that I quit busting out my meter to double check my exposure.

Changing the ISO from 100 to 200 is 1 stop. Decrease the power by on the light by moving the slider one f-stop.

Does that help?

It may also be worth mentioning the whole stop values. Most cameras have either 1/2 stop or 1/3 stop settings (usually you can select which one).

ISO whole stops are: (darker image)...50 100 200 400 800 1600 3200 6400.....(brighter image)
Aperture whole stops are: (brighter)... 1 1.4 2 2.8 4 5.6 8 11 16 22 32 45 64...(darker)
Shutter speed whole stops:(brighter) ... 1/30 1/60 1/125 1/250 1/500 1/1000...(darker)

So if you are at f/8, it may take 2 or 3 clicks to make the one stop change to f/11, as each click would make a 1/2 or 1/3 stop change.