Photo Tip – Understanding Portrait Photography Lighting Ratios!

Today’s portrait photography photo tip involves lighting ratios. Unfortunately, I’ve got some bad news. There’s going to be (gulp!) some math involved!

But don’t worry, it’s pretty easy.

We’ve been talking about lighting patterns and how important the shadows they create are to our portrait photography.

On one end of the spectrum, if there isn’t any shadow – it is very flat light and we lose most or all of our sense of depth and shape. Remember, it’s the shadows that define form. No shadows would be a lighting ratio of 1:1.

At the other extreme, if there is a shadow that is totally black, we lose all visible detail in the shadowed area. It is just one massive black area. This is a lighting ratio at or exceeding about 8:1.

And everything in between.

There really isn’t anything wrong with any particular light to shadow ratio. They all have their uses. A small ratio can help disguise wrinkles and acne – or just take the viewer’s attention off the model’s face and push it to the clothing. A large ratio can add drama and mystery to a photo.

The important thing is to recognize that lighting ratios are important to the viewer’s experience and to consciously make the decision of what ratio to use. PLEASE! Make the decision! Don’t let your camera or the conditions decide for you!

Here is how to calculate the ratio…

As we’ve been discussing, in our lighting set up the main light establishes the lighting pattern we want – short, broad, flat, split, loop, Rembrandt or butterfly. The lighting pattern also determines the shape of the shadow.

Our second light, the fill light – determines the depth of the shadow otherwise known as the lighting ratio.

By the way, keep in mind that when I say “light”, the source could be anything. It could be an on camera flash, off camera flash, studio light, reflector, window, candle… anything!

To determine the lighting ratio, all you have to do is first turn off or block the fill light and do a meter reading of the main light – all by itself. This can be an in camera meter or a handheld one. The key point is that you only measure the light from the main light.

Next, turn off or block the main light and meter the fill light.

Clearly, if the fill light is a reflector of some sort, you cannot turn off the main light or you will have nothing!

When I say to block a light, I mean to block it from the meter. You want to be sure that whatever light you are measuring is the only one affecting the reading.

The difference between the two is the lighting ratio!

If you have a 1:1 ratio it means that the key light and the fill light are of the same light intensity. An 8:1 ratio means that the key light is 8 times brighter.

Now for the – easy – math. Calculating the various exposure differences involves a factor of two. This goes back to the days of film.

A film (or ISO) speed of 200 is twice as fast as a film speed of 100. In other words 100 film requires one “stop” more light for exposure. It doubled in exposure value.

An ISO of 400 (200 doubled) is twice as fast as 200… and so on. 400 is two “stops” more than 100.

A lighting ratio of 1:1 is the same. 2:1 doubles the light and is one stop difference. 4:1 is double 2:1 and requires yet another stop. 8:1 is 4 stops difference from 1:1.

So to calculate the exposure differences, just multiply or divide by 2! A 5:1 ratio is 2 1/2 stops more than 1:1.

See? It’s easy as pie. (The kind you eat, not the mathematical pi which isn’t easy at all!)

Today’s portrait photography tip is designed to get you thinking about the differences between light and shadow (lighting ratios) and how they affect the viewer. While it seems to be a simple concept… it is really quite advanced.

With today’s photo tip – by choosing our lighting ratio – we’re starting to take control of our portrait photography by deciding on what sort of mood we want to impart. We are becoming artists, not snap shooters. This can’t happen with the camera on automatic!