metering the fill and main lights

[chocchip]

This is my first post so be gentle. I'm a bit confused when it comes to metering the fill and the main light. I understand that the fill light is the source that fills in the shadows and is typically the light that the camera is right next to or underneath. I may have misunderstood, but I thought my instructor said that you base your camera aperture setting on the fill exposure. For example, if my fill reads at f/8 and my main reads at f/11, (a 3:1 ratio), do I want to set my aperture to f/8? Isn't the light additive? Need some advice, help!

[BobbyG]

Originally Posted by chocchip

This is my first post so be gentle. I'm a bit confused when it comes to metering the fill and the main light. I understand that the fill light is the source that fills in the shadows and is typically the light that the camera is right next to or underneath. I may have misunderstood, but I thought my instructor said that you base your camera aperture setting on the fill exposure. For example, if my fill reads at f/8 and my main reads at f/11, (a 3:1 ratio), do I want to set my aperture to f/8? Isn't the light additive? Need some advice, help!

No you would set the aperture to f11...

Think of it this way...if you turned the FILL off you would have one light source metered at f11 and if you set the camera to f11 you would be properly exposed. You could,however, have areas that are underxposed and need some "fill" to properly expose those areas.

So now you turn on the "fill" light. If you set the aperture to its meter reading of f8, you have opened up the lens allowing for more light to hit the sensor...so NOW the fill side of the image is properly exposed at f8...BUT because the main is much stronger it will be overexposed and not give you the look you seek....

By keeping the aperture set to your "main" you are lessening the shadows but not eliminating them...the fill is simply adding light to a darkened area and adding depth to the image...

Hope this helps....

[chocchip]

Thanks Bobby G, that's what I had orginally thought. I must have misunderstood the teacher. With the same scenario above, if I took my meter reading (with both lights on) at my subject's nose, who is facing the camera, won't the reading come out to slightly higher than f/11 because the light is cumulative?

[BobbyG]

Yes it can and will in many cases. I use the ratio you described above a lot and I will typically set my aperture to f13 or so. Its a matter of preference...I like to shoot a hair underexposed...for my taste and style in post, underexposing gives me the look I like...

[Jeff_Green]

And who can argue with the look that Bobby ends up with?!

[Dobick]

Originally Posted by chocchip

Thanks Bobby G, that's what I had orginally thought. I must have misunderstood the teacher. With the same scenario above, if I took my meter reading (with both lights on) at my subject's nose, who is facing the camera, won't the reading come out to slightly higher than f/11 because the light is cumulative?

One point of correction here -- the light is not cumulative. If you have one light source and it meters at f/11, and then you add in three more at f/11, everything will be at f/11. If you added in ten more at f/11, the scene will still be f/11

[chocchip]

Okay, with 10 lights at f/11, how would one express that ratio?

[David_3]

Originally Posted by chocchip

Okay, with 10 lights at f/11, how would one express that ratio?

1:1:1:1:1:1:1:1:1:1

[bfphoto]

This is one topic that is really hard to understand by most new photographers. To really understand light ratios you have to go back to when we were using hot lights (some of us are going back to those now).

It all has to do with the inverse square law of light fall off, but I'm not about to try to explain that here. It can, however, be expressed in terms of f stops. Here's how. The fill light does light the whole scene, putting light on all aspects of the subject. The main light, key light, or what ever you want to call it adds the modeling contours to the subject and determines the "key" of the photograph.

Let's say the fill light is f 8 measured with a flash meter so that all the light falling on the subject is f 8 measured by it's self. If the key light (Main) is then measured at f 11 by it's self, then it is putting twice as much light on the subject from the side. You then have 1 unit of light from the fill and 2 units of light from the key, so 2 + 1 = 3, consequently a 3 to 1 ratio. Some will call this a 1 to 3.

So far you have taken meter readings of each light individually to set the ratio. To get the correct exposure you will need to take a meter reading with both lights firing with the dome of the meter pointed at the camera lens. Before you were pointing the meter directly at the lights. OK. Fill light reads f 8, main reads, f 11 and with my meter dome pointed at the camera, the meter now reads f 11 and 1/3 stops or on my camera f 13.

So Bobby is really not underexposed at f 13, but right on the money.

Now, if you are using hot lights of the same intensity, and the fill light is 8 feet from the subject, where would you put the main light to get a 3 to 1 ratio? No...it's not 11 feet, but rather 5.6 feet. Because of the inverse law of light fall off, 5.6 feet will give you twice as much light on the subject as it would at 8 feet. I'll understand if you are now totally confused. It took me a long time to get this concept through my thick skull, but once you understand it, your life will be much simpler if you are concerned about lighting ratios.

Hopes this helps some.

[chocchip]

This makes sense to me, although my initial response was to say that 4 feet would have been how close I needed to move the light to get twice as much light on the subject. I do recall one instructor mentioning the inverse square law, but he didn't go into too much detail about it.

Does any one else recommend situating the lights slightly above the subject's head (vs. directly at the face?)

[bfphoto]

That's why it's confusing. At 4 feet you would have 4 times as much light as the light at 8 feet, therefore, 4 units plus 1 unit from the fill equals a 5 to 1 ratio. As far as the height of the fill, it really doesn't make a lot of difference so long as it is close to the camera axis. You just should be using a broad source of light like an umbrella.

[nyphotopro]

This month's Shutterbug (October 2007), which just showed up, is dedicated to Lighting. It has some good articles that may help you.

Best wishes,

[BobbyG]

Originally Posted by chocchip

Does any one else recommend situating the lights slightly above the subject's head (vs. directly at the face?)

Again, a matter of preference and a matter of duplicating a style...

If shooting with one light and you wanted to get that "butterfly" effect so common in portraits, yes you would put the light HIGHer than the camera axis shooting somewhat downward. The shape of the nose would leave a slight butterfly shaped shadow which is pleasing to many...

Take that same light source and move it to the right and higher still...shooting ACROSS the face instead of straight on...and you can create "Rembrandt" lighting...take the same light and move it well BELOW the models face (shooting upwards) and overexpose a bit and you can create the Hollywood horror film lighting...

So each lighting position has its place...its just a matter of the look you seek during that particular set....

When I shoot my commercial headshots I use 3 lights and a BUNCH of foam core...





This setup is one that gets rid of ALL shadows...makes for a very clean looking image and for actor headshots and such, this works great...BUT it's not a portrait set up per se...

Here is a test example of the lighting this setup provides...



If you notice, the main is WAY above the camera axis, yet there are no shadows due to the foam core "filling" the subject with reflected light...

[J Eddington]

Wow, THAT was one of the best descriptions of lighting I have ever heard! Most up to now have sounded like plaaaaa, plaaaaa, Plaaaaa. Now I just need to unpack that lighting system I bought 4 months ago and find a victim (uh, I mean model)
Thanks guys

[chocchip]

That's the first time I've seen a softbox (as opposed to a grid) used for a hair light but the effect is lovely. It looks as though the lighting is set up for butterfly, but you managed to almost get a broad loop in the first shot by turning the model's head slightly and using the foam core to fill in the shadow below the nose.