Tips & Techniques 1 - Exposure Control


First of all you need to realize what exposure exactly is, what it does and how you can control it if you want to shoot perfectly exposed pictures. We always found it very useful to visualize. What is what and what does everything do? In a digital camera the sensor is what the film was in an analogue camera. It needs light to be able to capture a picture. After all photography means 'writing with light'. Anyway, the sensor needs the exact right amount of light so you get a perfectly exposed photo. In the same situation you can let the light in through a very wide opening for a short period or you can let the light in through a very narrow opening for a longer period. Both will give you the same and correctly exposed photo if the values are correct. The opening is the aperture (the f-value), the amount of time you allow to let the light go through that opening is the shutterspeed.

Like we suggested before: it's best to visualize to understand. Therefore we like to compare photography to everyday life things. Think of the sensor as a drinking glass, the aperture as the flow of water coming from a tap and the shutterspeed as the amount of time you open that watertap. You have to fill the drinking glass exactly up to the edge to perfectly expose a picture. If you you poor in too much water and it flows over the edge, you overexposed the photo. If you don't fill the glass up until the edge, you underexposed the photo. If you want to to use a very powerful flow coming from the tap (= a very wide aperture) you accordingly need to adjust the time the water flows from that tap (= shutterspeed) to ensure a perfect exposure. A powerful flow will need a shorter running time to fill up the glass to the edge than a less powerful flow will need. Always keep in mind that the trick is to fill the glass right up to edge. It doesn't matter if you do that with a powerful flow, a mediocre flow or a very weak flow. Just be sure you fill up that glass to the very edge and don't cause the water to spill. If you don't fill the glass entirely you underexposed your picture, if you spill water you overexposed your image.

The light meter

There are two main meter types: the hand-held meter and the meter that is built in your camera. We will be concentrating on the built-in meter. Obviously there is a big disadvantage when it comes to the hand-held meters as we often use filters, extension tubes or anything else that changes the light coming through the lens. A built-in meter is always a reflected light meter. It always sees and reads exactly what the lens sees and therefore we will use that meter type. Besides, it comes with every camera and therefore it's for free!

This sounds really good, but why do we have to learn about exposure control then? Why do we even have to bother about exposure control? Why don't we let the light meter that's built in our camera decide what settings to use? The meter controls the exposure for us, right? Well, obviously because the light meter doesn't know what it 's looking at! It is able to measure the reflected light, but that's about it. The meter doesn't know whether it is looking at a scene which reflects loads of light or just a little. The people who constructed the light meter decided it was best to make the meter believe it is always looking at a typical landscape scene, a so-called average scene. This was a very good idea as a lot of scenes are average scenes (otherwise it wouldn't be called 'average'!). As it happens to be the amount of light reflecting from such a typical scene is about 18 percent. Therefore they used this value to calibrate the light meter. What the light meter is trying to do to every scene (and this is important to grasp!) is trying to expose the scene in such a way that this scene reflects about 18% light. We call these scenes 18% gray and the light meter has no troubles in getting these average scenes perfectly exposed.

And if everything we wanted to photograph would be average or if we would only take pictures of objects that reflected exactly 18 percent light, exposure problems would never occur. Unfortunately this is not the case and therefore we will have to understand the objects and scenes we want to photograph, we have to understand what our light meter does, how it works and how we can control the exposure.

Beginning to understand the backward trick

Okay ... so far, so good. If you point your camera to a scene which is about 18% gray, you are happy with the job your light meter has done. If you use your camera to shoot a black swan however, be sure you will be unhappy! This swan will not be black on your photo if you let the meter decide what settings to use, the black swan will look gray! This is very logical as the light meter wants the swan to look 18% gray, remember? The opposite will happen when you shoot a white swan. This white swan will also look grayish instead of the pure white it is in reality. Again the 18% gray obsession of the light meter kicks in.

To get real black swans and real white swans, you have to understand what the meter did to the settings to produce the gray swans. In the case of the black swan, the meter had to OVEREXPOSE the scene to get a gray swan. The extra exposure lightened up the black swan so it became gray; 18% gray. The opposite happened to the picture of the white swan. The meter let in less light than needed and UNDEREXPOSED the scene to get yet again a grayish swan. To actually obtain a white swan, you need to give MORE exposure, about one f-stop more. If you want the black swan to stay black, you need to allow LESS exposure than the meter suggested; about one f-stop LESS.

If you don't want to change the aperture (f-stop), you can also change the shutterspeed of course. Remember to use a SLOWER shutterspeed if you want to OVERexpose and a FASTER shutterspeed if you want to UNDERexpose. The same obviously applies for the aperture. Use a SMALLER aperture (a higher f-value) to UNDERexpose and a WIDER aperture (a lower f-value) to OVERexpose.

It all seems so backwards and many people have troubles in processing the exposure theory in their brain. Don't think you are alone in this! Most people think, when shooting a scene in the snow, that all this white will cause overexposed scenes as the snow is so bright and reflects so much light. They most likely UNDERexpose these scenes and are gutted to find out they will get gray to even blackish snow. "How is that possible?!", they think. Well, if they had remembered the trick the meter did, they would have found out it is not that difficult to grasp. The white snow reflects a lot of light, way more than the 18% which is average. Therefore the meter will tell the camera to UNDERexpose the snow-scene to still get that 18% gray. See? The snow will look grayish on your photo if you rely on the meter. Underexposing even more (because you didn't understand the backward trick) will make it even worse and will leave you with dark gray to even blackish snow.

Doing the trick yourself

There are a few simple ways to get the right exposure by still using the built-in meter. If you use one of the following tricks, your black swan will be black, your snow will be white and your white swan will be too.

First, you can buy a so-called gray card. A gray card is exactly 18% gray and therefore reflects exactly 18% light. The perfect tool to ensure you always have something up for grabs which has the perfect mid-tone. When shooting a black swan, you hold the gray card in front of the swan, so the light hits the gray card in the same way it is hitting the swan. You read the settings the meter suggests when it reads the light off the card. Then you set the camera to manual exposure, remove the gray card and use the same settings the meter suggested when it read off the gray card. Ignore the warnings the meter will give you. Obviously the meter will think (now the gray card is taken away) the scene will be underexposed. Nothing is less true. Press the shutterbutton. Using these settings will create a perfectly exposed picture. Like a trick by Hans Klok, the swan is as black as it should be. By using the gray card, you have calibrated the meter for the light hitting the swan. The meter doesn't know the reflectance of the swan, but it DOES know the reflectance of the gray card (as the gray card is exactly 18% gray), so the exposure is perfect! Of course you can also use the gray card when shooting a white swan. The opposite will happen: the meter will warn you for overexposure as soon as you take away the gray card and set the camera to manual exposure. The result will be the same; a perfectly exposed picture.

The second option you have, if you don't have a gray card or don't want to buy one, is looking for something middle-toned (18% gray) in the scene that's in the same light as the swan. Take a reading off this substitute gray card (you have to use spot metering if that's an option on your camera), recompose on the swan and press the shutterbutton. Green grass for example is always 18% gray and often provides you with a natural gray card. The same goes for concrete and a perfect blue sky. Please understand that the reflectance of grass can vary if it's wet.

The third option many writers and photographers give you is reading off your own hand. A hand is about twice as bright as a gray card. After you took a reading off your hand (hold it in the same light as the object you are going to shoot, just like you would do with the gray card!), you open up one stop (as a hand is about twice as bright as 18% gray) to perfectly expose the scene. We find this an inferior option as it obviously only works for photographers of the caucasian race.

As a last resort, if none of the beforementioned tricks do the job for you, you can usually just close down one stop from the reading for a black subject or open up one stop for a white subject.

Snow scenes

Snowy scenes are especially diffifult to get right, as snow is approximately 2,5 stops brighter than 18 percent gray. Using a gray card in snowy scenes will give you pure white snow. The gray card works perfectly, but because pure white snow has no texture or detail whatsoever, you need to slightly underexpose such a scene. To get the exposure of a snow scene just right, you need to read the light off a (substitute) gray card and give one f-stop LESS exposure than the meter suggests. The snow will get structure because of this slight underexposure. You can also measure directly, forget about the (substitute) gray card and overexpose the scene by 1,5 f-stop. Either way will give you 1 stop underexposure (from 18% gray!) and thus giving the snow some texture.

A last tip

Obviously most of the time, you won't be shooting black or white swans but something in between or maybe even a little of both. So, just figure out how close to 18% gray your subject or scene actually really is. You can always use your graycard, your own hand or the grass on the soccerfield.