metering when you have multiple lights

drvnbysound wrote in post #14712472
I think I am following this correctly, but I'm either missing something, or I dunno...

If you want a 2-stop difference between your fill and key lights, you want your fill to be at f/4, and you want to shoot at f/8. You start by metering your fill light until you get it at f/4. Next, you add your main light, and adjust until your meter reads f/8. Am I correct in saying that you actually don't have a 2-stop difference? Because, what you have metered is the combination of your fill and your key to get to f/8, so the key light is actually less than f/8... right?

The fill hits where the key doesn't. That's f/2.8. Where the key and fill hit, it's F/8. When individually metered they're not two f stops apart. When the light hits the same surface, it is.

A lot of it depends on where the light is and how you meter, but this gets you good exposure the first time, but I consider it to be rather safe.

windpig wrote in post #14712540
go here
http://super.nova.org/​DPR/Ratios/

Great article.

What I don't understand is the last portion (Step 3 - Make the Exposure Reading) of the example on metering... "Make a mental note of what a 3:1 ratio looks like by eye. " I don't really follow the purpose for this... just because?

The exposure reading is exactly as described - the combination of the key and fill falling on the subject. At this point, if you want your shooting aperture to be different than what the meter reads for a correct exposure, you can adjust the lights [By the same amount - keeping the ratio the same] to the aperture you would like to shoot at.

bdillon wrote in post #14712096
I always start with my fill light. If I know I want my fill light to be three f stops under my key and I know I want my key to be f/8, then I meter my fill for 2.8. If I wan't two f stops, I start at f/4 with my fill, and so on.

Hair and background are to taste, however, if you want repeatable results that looks good for things like directories and yearbooks, then I meter to the hair light to match my key, measured from the crown of the head, and my background light to match my key at shoulder height.

After all that I kick my key on and meter f/8. If I had started with the key at f/8 then added a 2.8 fill, I wouldn't have f/8 anymore. More like f/10. The light is additive.

bdillon wrote in post #14712549
The fill hits where the key doesn't. That's f/2.8. Where the key and fill hit, it's F/8. When individually metered they're not two f stops apart. When the light hits the same surface, it is.

A lot of it depends on where the light is and how you meter, but this gets you good exposure the first time, but I consider it to be rather safe.

This was pretty much my point... If you want a known stop difference between your key and fill, you don't actually get that with the method you described... you would probably get close to that difference and a proper exposure reading.

drvnbysound wrote in post #14712689
This was pretty much my point... If you want a known stop difference between your key and fill, you don't actually get that with the method you described... you would probably get close to that difference and a proper exposure reading.

Right. In cases where I want a known ratio between lights I meter fill and key separately, then meter them both together to get my exposure on the camera. If I ended up with f/11, I'd then meter my hair light to f/11 on the crown of the head and my background light f/11 at waist height. I believe I said shoulder height first time.....I had a brain fart. I measure at the waist for typical portaits.

drvnbysound wrote in post #14712472
I think I am following this correctly, but I'm either missing something, or I dunno...

If you want a 2-stop difference between your fill and key lights, you want your fill to be at f/4, and you want to shoot at f/8. You start by metering your fill light until you get it at f/4. Next, you add your main light, and adjust until your meter reads f/8. Am I correct in saying that you actually don't have a 2-stop difference? Because, what you have metered is the combination of your fill and your key to get to f/8, so the key light is actually less than f/8... right?

You got it.

To get a two stop difference between fill and key, you set one at f/8 and one at f/4 metered separately.

When you meter both, you'll get something like f/8.1 and that would be your exposure.

bdillon wrote in post #14712549
The fill hits where the key doesn't. That's f/2.8. Where the key and fill hit, it's F/8. When individually metered they're not two f stops apart. When the light hits the same surface, it is.

A lot of it depends on where the light is and how you meter, but this gets you good exposure the first time, but I consider it to be rather safe.

If the Fill is set up properly to illuminate the entire face, even though 'source intensity' ratio is 4:1, the highlight side of the face gets light from both Fill and Main, so 'subject contrast' is 5:1

As drvnbysound has said, "The exposure reading is exactly as described - the combination of the key and fill falling on the subject..."

Well I finally had a chance to post some pics of my setup today. See below.

Following the advice in this thread I metered my fill light (on my left looking at the subject) to f/4 and then added my key light until I metered f/8 for both combined. I then added my background light at the lowest setting, and my hair light (using a snoot) at max power.

In the quick-and-dirty test shots of my subject below, the first shot is with no background light, the second shot is with with a basic reflector, and the third is with a 40 degree grid that I just acquired the other day. Its obvious the grid makes a huge difference in control the light spill. (It also helped a little when I steamed the wrinkles out of the backdrop).

Any suggestions for improvement given my limited space issue?

Should I consider using a grid for my hair light? If so, I'll have to buy another grid reflector.

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bdillon,
Your Main and Fill light placement is entirely too far from the subject, so that you are losing the value of using a softbox modifier to soften the light source...a softbox should be used within about 2-3x its largest dimension, in order for it to be a 'soft' source.

Wilt wrote in post #14745929
bdillon,
Your Main and Fill light placement is entirely too far from the subject, so that you are losing the value of using a softbox modifier to soften the light source...a softbox should be used within about 2-3x its largest dimension, in order for it to be a 'soft' source.

The tape-measured distance is 10 feet. I think the pics of my setup are deceiving. I shot them with my 24-70L. Is 10 feet too much?
If I moved them in closer (which would require moving my couch), how do you anticipate my shots will change in appearance?

coeng wrote in post #14745956
The tape-measured distance is 10 feet. I think the pics of my setup are deceiving. I shot them with my 24-70L. Is 10 feet too much?
If I moved them in closer (which would require moving my couch), how do you anticipate my shots will change in appearance?

Using the proportional size vs. doorway in the background, I'd estimate the softboxes to be no more than about 16 x 22" softboxes, so in order for that source to be 'soft' they should be no more than 4-5' away from the subject. The change...much softer shadow edges, if any. You can see the shadow cast on Mickey's right cheek, and the right thumb shadow on his hand that the shadow penumbra (edge) is fairly well defined.

I'm with Wilt.

Wilt wrote in post #14745929
coeng,
Your Main and Fill light placement is entirely too far from the subject, so that you are losing the value of using a softbox modifier to soften the light source...a softbox should be used within about 2-3x its largest dimension, in order for it to be a 'soft' source.

Fixed that for you.

You to bdillon...............​not

Also, get your hair light in as close as you can, and control the spill more with a tight grid or snoot.
Inverse square law stuff. The closer that light is, the faster it will fall off and not be as detectable in the expsoure. This is why I love a boomed, gridded softbox as a hair light. You can get it in super close and if it does leave a shadow line, it's soft.

Having fixed the distance, the other thing I would suggest is that Fill is more along the camera axis, not 30-45 degrees off axis. The shadowing it creates by being off axis cannot be totally eliminated by the Main...there will always be a remnant of shadowing cast by the Fill.