Metering with 2 lights

LRussoPhoto

Been shooting with strobes for a while now but usually did it by trial and error. I am learning to use a light meter. If I'm using 2 light to light a subject, say a key camera left the a second to just fill camera right, I know a lot of people say your fill should be about a stop or so lower then the key. When I meter my second light, do I also have the key light fire for the meter reading too? Or do I just fire the fill light and mater it a stop lower then the key? I'm kinda thinking that if I shut the key light off and just fire and meter the fill light, when I take the real image the fill light will be too bright because the light from the key light will be spilling and affecting the fill light side too? Any I correct?
So the question is, when using multiple lights do I fire them all when I take my metering reading for each light?

kdog

You're not quite looking at it right. There's more overall light with both lights turned on, but your ratio will stay constant. So do this. Measure them one at a time. Set them a stop apart. Then take a meter reading with them both on, and set your camera to that.

LRussoPhoto

kdog wrote: »

You're not quite looking at it right. There's more overall light with both lights turned on, but your ratio will stay constant. So do this. Measure them one at a time. Set them a stop apart. Then take a meter reading with them both on, and set your camera to that.

Ok, so say my key meters at f11 and my fill meters at f8, i have my fill one stop under. But when I meter both together obviously when I take this meter reading, I'm pointing the meter at the camera right? Any, what if that meter reading says f16 but I want to shoot at f11? My lights are both set too high for my desired shooting aperture. Would I just lower each light buy the 1 stop to get them down where I need them? I mean I dont know if that meter reading is possible, but what if something like that happens, in either direction really?

ziggy53

The way I set up for a multi-light shoot is to set the key light first. The exposure will mostly depend on the key light alone. Then, set your fill, which is typically 2 to 2-1/2 stops less than fill (Loop and Split lighting).

Next add rim or hair lights, background light(s), etc. Realize that these additional lights may "spill" extra light into the scene, especially if you shoot indoors in a smaller room with light walls and ceiling and if your light modifiers allow a lot of spill. (Simple reflector/diffusor modifiers like an umbrella, for example, have lots of spill, while a soft box may have little if any spill.)

After all lights are in place, make one final light meter test and one final sample shot to both determine lighting suitability and overall exposure. Repeat as needed to change the lights in order to meet your lighting goals. ("Rembrandt" lighting is much different from typical "Loop" lighting, for instance.)

Your light meter type and how you use it will determine, in part, how many samples you need for an accurate determination of the scene illumination.

A very nice lighting primer:

http://www.sekonic.com/whatisyourspecialty/photographer/articles/the-five-basic-portrait-lighting-setups.aspx

Before you depend on a hand-held light meter for exposure, be sure to calibrate the hand-held light meter with your camera's meter. A hand-held Incident Light meter may show somewhat different results compared to the Reflected Light meter of your camera. While both are designed to represent middle gray exposure, it's typical for there to be a discrepancy.

http://www.bhphotovideo.com/find/Product_Resources/lightmeters1.jsp

LRussoPhoto

So your saying fire each light by itself, with out any of the other lights firing right?

ziggy53

LRussoPhoto wrote: »

So your saying fire each light by itself, with out any of the other lights firing right?

Yes, fire only the key light and base the basic exposure off that to start. Set each additional light output individually, using your meter to determine when they are at an appropriate ratio to the key light.

When all lights are set, turn all lights on and meter from the subject position. The resulting exposure should be similar to the original key light exposure, plus the additional light from all sources including indirect light from spill.

Repeat the procedure in order to fine tune any lighting changes in either output or position of any lights.

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Edit: I should add that the above procedure is for manual studio monolights or pack lights. Any lighting which may be controlled from the camera's exposure system should use both the camera manufacturer recommendations and the light manufacturer recommendations.

kdog

LRussoPhoto wrote: »

Ok, so say my key meters at f11 and my fill meters at f8, i have my fill one stop under. But when I meter both together obviously when I take this meter reading, I'm pointing the meter at the camera right? Any, what if that meter reading says f16 but I want to shoot at f11? My lights are both set too high for my desired shooting aperture. Would I just lower each light buy the 1 stop to get them down where I need them? I mean I dont know if that meter reading is possible, but what if something like that happens, in either direction really?

Sure it's possible. Just pre-compute the setting for each light in advance. Remember, doubling the light increases the light by one stop. So if you had two lights set at f/8, you'd have your camera aperture of f/11. Now just increase your key light by a half stop, and decrease your fill light by a half stop, and voila. You've got f/11, with the lights one stop apart.

LRussoPhoto

If my lights are set at f8 and I set my camera at f11 wouldn't I be under exposing the scene by one stop?
And u lost me after that, my lights only go in third stop increments. Plus I don't get your math with going up and down a half stop from f8 gets u f11.

kdog

LRussoPhoto wrote: »

If my lights are set at f8 and I set my camera at f11 wouldn't I be under exposing the scene by one stop?

No, and this is the crucial part. Two lights at f/8 gives you twice the amount of light, which is f/11. Four lights (at f/8) gives you f/16. Any stop of light is double the previous stop.

And u lost me after that, my lights only go in third stop increments. Plus I don't get your math with going up and down a half stop from f8 gets u f11.

Ok, so now you understand that having two lights at f/8 gives you f/11. So if you reduce one light a little, and increase the other light by the same amount, the average power output of each light is f/8. So you're still at f/11.

It's like having 4 quarters in each of your two front pants pockets. You have $2.00 total. So if you take one quarter out of one pocket and put it in the other pocket, you still have $2.00, but you have $1.75 in one pocket and $2.25 in the other.

Don't forget that distance affects light output too. So even if your lights can only be adjusted in third-stop increments, you can tune this by changing the distance of a light to your subject. You could simply move one f/8 light a little closer, and one further away to get your one stop distance. Light falls off with the square of the distance, so doubling the distance of a light to your subject decreases the amount of light one stop.

Also don't forget that the modifier you use also changes the output of the flash. You may be using direct flash, umbrellas, softboxes, etc, and they all have different amounts of light they will pass.

LRussoPhoto

Wow, that is great info. Makes total sense now, thank you.

kdog

LRussoPhoto wrote: »

Wow, that is great info. Makes total sense now, thank you.

Glad to help!