Wim van Velzen photography - articles

1/219 sec at f 13,043 and 7 meter 12

exposure and focus - part 1

Part 1: lightmetering and exposure

Part 2: focussing and sharpness

Part 3: real life situations


This article about lightmetering and focussing are written from the perspective of a landscape and reportage photographer. I don't have any experience in the studio.
Therefore lighting, flash light metering etc. are not discussed.

This article doesn't deal with the aesthetic side of light and colour. See light in landscape photography and the use of colour.


There is a lot to say about the technique of making photographs. The average camera of the year 200X has more technique and electronics inside than the entire Apollo space program. This all can seem overwhelmingly complex.
But actually it all boils down to a few things: choosing the shutter speed, aperture and distance. Everything else (OK, almost) is derived from these. Therefore this article about the basics: metering the light, exposing and focussing.

some definitions first

Light metering: metering the amount of light that hits the subject or that is reflected by the subject. The light metering is rendered in a combination of shutter speed and aperture, of in a certain light value (a lot of separate meters work this way).

Exposure: the combination of aperture and shutter speed, making a certain amount of light hitting the film or chip.

Lighting: the light hitting the subject; lighting can have all shades of colour (e.g. daylight and candle-light, see below) and qualities like harsh or diffuse.

Light values: expresses the amount of metered light, defining what combinations of shutter speed and aperture making a certain amount of light hitting the film or chip (at a given film speed).
For example: using a 100 ISO film, you meter light value 15 (EV15). In that case a good exposure would be f16 @ 1/60, or f11 @ 1/125 or f8 @1/250 etc.

Shutter speed: the period of time light can fall through the lens on the film or chip. The classic series is 1 second, 1/2 sec., 1/4, 1/8, 1/15, 1/30, 1/125, 1/250, 1/500, 1/1000 and to the longer side 2 seconds, 4, 8 Each step either way in the series means two times as much or two times less light.
Electronic cameras enable to choose values in-between, like 1/90 or 1/350.

Aperture: the light gets through the aperture to the film or chip. This aperture is defined by its diameter, divided through the focal length of the lens. This sounds far from easy, but it means that the same amount of light gets through a wide-angle lens @ f8, as through a telephoto-lens @ f8. The fact that the latter has a diameter of 25mm and the former of 3mm is not important.
So the size of the aperture is defined by the relative diameter of the aperture. But the amount of light gets through the total area of the aperture. That means that four times as much light gets through an aperture of 8mm as through a 4mm aperture: the area of the aperture is four times as large, not two times!
Therefore the aperture series is f1; f1.4; f2; f2.8; f4; f5.6; f8; f11; f16; f22; f32. Each step either way means two times as much or two times less light. The larger the number, the smaller the aperture and the less light!
All cameras and lenses enable to choose values in-between.

Stop: photo speak for the relation of e.g. 1/125 and 1/250, or f11 and f16. In both cases, the difference is one stop. Between 1/125 and 1/500 there are two stops, etc.

Fuji superia 1600 @1000; 50mm @ 1.4 Film speed: not every film needs the same amount of light; chips can be set in camera to a specific speed.
Film that needs relatively little light is called high sensitive or fast film; film needing more light is called (as you could have guessed) low sensitive or slow film.
Film speed is given in ISO. Slow film is for instance ISO50/18 or ISO100/21; faster is ISO400/27 or ISO800/30. [ The ISO names are in fact derived from the older American ASA and German DIN: ISO 400/27 actually is 400 ASA or 27 DIN; most of time only the first number is used - the ASA one. ]
Fast film has a character, different from slower film, like more grain and less detail. I will not discuss this any further here.

high contrast scene; the veil contains no detail, but I still like the atmosphere Contrast: some parts of a subject reflect or receive far more light than other parts (like a bride in sun light and a groom in a shadow area). If the contrast between the brightest and the darkest parts is too large, than the film or chip can no longer render both correctly (the human eye is better in this respect).
It is therefore important to know how much contrast a film or chip can handle and to meter the contrast is within a given subject
Suppose the lightmeter meters 1/250 at f8 for the bride in the sunlight and 1/4 at f8 for the groom in the shadow, than the contrast is 6 stops. This is more than most films can handle without problems, so you could decide to position the bride in the shadow too.
Below there is some indications given about the amount of contrast films can handle.

Overexposure exposing longer, of at a wider aperture than is indicated by the lightmeter.
When the meter, for instance, says f8 at 1/250, and you set the camera at f8 at 1/125 (or 5.6 at 1/250), then you make an overexposure of 1 stop.
Underexposure exposing for a shorter time or at a smaller aperture than indicated by the meter.
It is very important to know exactly what is meant by over- and underexposure! Suppose you take a photograph of a white fungus on a dark tree. Both parts of the image differ from middle grey to the same degree. Spotmetering the fungus gives 1/250 @ f16. A metering on the tree gives 1/15 @ f16. The right exposure is therefore 1/60 @ f16.
In other words: the photographer meters the fungus and exposes two stops over (or he meters the tree and exposes two stops under). This is a different kind of over- and underexposure than in the case he had exposed at 1/125 @ f16. Then he would have exposed one stop under the correct exposure.

In brief: you can meter a part of the subject and consciously expose under or over in relation to the metering, in order to get the correct exposure. The photograph will be according to reality.
One can also expose under or over in relation to the correct exposure, and so harm the picture!


several ways to meter the light

There are several ways of metering the light. I will discuss them here. In the next chapter I will deal with the work flow that is involved with all these ways.

Incident light
Principally this is the purest form of light metering: you meter the amount of light that hits the subject. You can do this by means of a separate lightmeter (outside the camera) pointed at the light source, which meters the incident light and indicates right combinations of shutter speed and aperture.
You can do the same with a metering camera, if you use it to meter a so called grey card. This is a card with a neutral grey colour. The card has the same reflection as the average subject - the value to which the camera meter is adjusted by the factory (18% grey). You put the card in the same light as the subject, point the camera to the card and meter the amount of light.
You can do the same without a card, by pointing the camera to the palm of your hand (unless you are gardening!). The value indicated by the camera is about one and a halve stop brighter than 18% grey (a sheet of white paper will be two and a halve stop brighter).

Reflected light
Using this method, you measure the amount of light reflected by the subject. This is the easiest way to meter with a camera, because you will always point the camera towards the subject!
This method is less pure, because the amount of light you meter, depends on the subject. A black cat reflects less light than a white one and as a photographer you want the black cat to be black on the photograph and the white one white - not the same middle grey.
Therefore, as you meter the reflected light you have to think whether your subject is about average grey, or that you have to over- or underexpose compared to the metered value (by the way, the black cat should be underexposed, and the white one over). Reflected light can be metered with a spotmeter or a meter in the camera (most incident meters can be set to reflected light too). A camera's meter can get you an integral metering (for the entire subject) or a spotmetering (only a small part of the entire subject). A lot of modern cameras sport a so called matrix metering: the camera meters the light values of several parts of the entire image, compares these values and defines the most likely exposure by means of the camera's software.


when to use which way?

So now you have several ways to meter the light. But when should which way be used? Is there any best method?
Again I discuss the metering ways, now from the perspective of usability.

Separate light meter for incident light: the best thing about this method is that you meter independent from the subject. You meter the light, not its reflection. The subject may be dark, light or spotted - it doesn't matter. If you are working with constant light - like a portrait series on an overcast day - you just have to meter once and set the camera accordingly.
The bad thing is that you have to be in the same light as the subject. There is no way to do this when you stand behind a window and want to photograph a market square, or a sunrise on the mountains, taken from a valley still in darkness. Landscape photographers don't use this kind of meter much, while a lot of portrait and fashion photographers do.

Grey card metering: here the same applies of course. And you have to take the card with you (there are little 10x15cm ones though).
I myself sometimes use the palm-of-my-hand method to check things when I am in doubt. If the metering of my hand tells me the same as the reflected light metering, I know I will be safe!

Bunessan 5 Spot metering: this has a totally different work flow. You often meter several parts of the subject and define an average (like in the case of a white dress and a black suit). Another way is to proceed from a certain exposure and 'scan' the subject to see how much different parts differ from the shutter speed and aperture combination you have in mind. If everything stays within two stops over and under (see also below: exposing print film and slide film, you will have a good exposure. You can also see if the shadows will be pure black, which happens when these parts are three or more stops under.
This method is used by many landscape photographers, because they often work with high contrasts where they have to decide to expose for the brighter parts or for the shadows. And as the distance between camera and subject is often quite long, the subject might well be hit by more or less light than the photographer.

I use this method also for weddings and events, because I am totally used to it. I use the spotmetering options of my cameras. Their angle of view is wider than of most separate meters, but it means one thing less to buy and bring along.
You will find more about my personal work flow in part 3.

Integral metering: this one works the same ways as a spotmeter, but the angle view is far wider. Consequently, the entire subject is metered. You will have to define how much your subject-as-a-whole differs from 18% grey, and over- or underexpose accordingly.
You need therefore a lot of experience if you want to use this method (less so if you use print film, which has a wider exposure latitude!).

Matrix metering: because of the software, there is no experience needed. That is least what the marketing guys tell you. The camera decides on its own what kind of subjects it sees and how much that subject differs from 18% grey.
And I have to say, most of the time the software is right. But the photographer never knows what the camera 'thinks'. You can never be sure the camera understands that you want to show the rainy sky as dark-threatening or that the foreground is of prime importance!
Reason enough for most photographers to learn how to meter themselves, be it with an incident meter or a spotmeter. For most subjects the matrix metering is more than adequate, especially for use with print film. And it works very fast.


exposing print film and slide film

To make things even more complicated, one has also to take differences between print and slide film into consideration.
Actually it is even worse, as digital cameras have their own metering and exposing characteristics. I want talk about that though, as that depends very much on the camera.
[ Very, very generally spoken one could say that shooting in jpg meters in the same way as slide and raw as print film. The digital worker is also very much helped by the histogram, that shows the ratio of brighter and darker parts graphically. If that ratio is not according to the subject, you can always make a new shot with a different exposure. ]

Slides are a final product, which cannot be changed. What is too bright, is to bright and lacks detail; what is too dark, is too dark and without any detail. Print film is, well, printed and one can correct some over- or underexposure. But only to a certain level: if a negative is really underexposed, you can print for shorter period, but that won't bring you any detail in the shadows. The shadow parts just don't contain any detail.

As a rule of thumb one could say that half a stop from the best exposure is still acceptable for slide film. More overexposure will cause the highlights to be just transparent, with no detail left. In projection you will only see the white of the screen and that is bad.
More than half a stop of underexposure does give saturated colours (everything is darker and more 'weighty'), but it doesn't sparkle anymore. Shadows are just plain black, totally blocked up.

Another rule of thumb is that the bright parts (clouds, white cloths, snow) you want to have detail, should be about two stops brighter than the exposure. In other words: if you meter f16 @ 1/250 for the white part, than f16 @ 1/60 will be the correct exposure. As they often say: 'the shadows in slides take care of them selves'.

There is by the way a difference between films: a film like Fuji Velvia 50 is high contrast and has therefore little exposure latitude. Fuji Astia, developed for portraits and true colours, is less contrasty and can handle more over and underexposure as a consequence. Something that is three stops brighter than 18% grey has still some details in an Astia slide, but it hasn't in an Velvia one.

Print film can handle much more deviation in exposure than slide film can. Overexposure in particular is no problem. Even three stops of overexposure renders negatives that can be printed without too much hassle; the prints will just have a little less sharpness.
Underexposure is more of a problem. One stop can mean ugly, murky, detaill-less shadows. So in case of doubt: err on the side of overexposure! I myself always set the ISO value in the camera two thirds stops lower than what the box says. So NPZ 800 is set as 500, a 400ISO film as 250 etc. Afterwards I have the film develloped as usual - so no pulling.
Doing this, means less chance of underexposure and the colours are a bit more saturated too. Be careful though: with print film only!

There is a rule of thumb here, exactly the opposite of the slide film one: dark parts of a subject, like shadow, black cloths and the like, should be two stops darker than 18% grey. Then they still are fully detailed. In other words: if you meter a black suit as 1/15 at f11, then the correct exposure will be 1/60 at f11.

And again like slide film there are high contrast and low contrast films. I use the latter as my normal film for portraits and when using flash (which tends to be harsh) - in other words at almost all shots where people are the main subject!
High contrast films can be put to good use for landscape and nature - although a lot of photographers (like I myself) use slide film for that. The high contrast of certain print film is by the way very fine, when you want to camouflage the quality of your so-so zoom lens or P&S camera... The prints still look punchy! (But with little detail or subtlety, mind you.)

Sometimes under or overexposure helps to intensify a certain atmosphere: underexposure can give a scene an eerie look, overexposure makes things more like summer and warmth. When doing this with print film, please tell the lab. Otherwise they will helpfull as they are compensate for your 'error' at the printing stage!


colour temperature

So far about metering the light and exposing. There is something else that has to do with the light: colour temperature. Here is give a brief description.

Light not only has quantity, but also a quality known as temperature. As a photographer you will have to know something about this, when you shoot for instance a portrait of your grandchild in tungsten light. When you get the photo back from the lab, or see it on screen, you will probably be surprised to see the child's face all yellow! Or this: you take a picture of your girlfriend, relaxing in a piazza As it was very hot that day, you both sat in the shadow. As soon as you get to see the picture, doubt strikes you: is your girlfriend that blue? We had been on the beach all day!

What happens? Is your camera wrong? The lab? Do you need to go to the optician?
Relax - nothing wrong. The film sees the colours as they are, while our eye and brain correct to what we know. In other words: tungsten light is yellow, and therefore the child's skin. But we know our grandchild isn't yellow, so we simply don't see it as such.
But seeing the photograph, isolated from the light source it was taken in, our brain doesn't correct and we find the child far too yellow.

The same applies, but now the other way round, for the portrait taken in the shadow. The light your girlfriend was sitting in was blue - the blue of the sky; the yellow colour of the sun didn't hit the shadow part of the piazza. And the film just sees that blueness
Fluorescent light is even worse - most of these lamps have little or no red in their spectrum. Therefore everything in their light looks green. If you don't believe me, just notice from the outside the colour of the lights in an office or fitness building at night. It really looks green!

This phenomenon is known as colour temperature. To express the kind of colour temperature, physicians refer to the colour of a black body that is heated to a certain temperature (in Kelvin, not degrees Celsius). In other words, when you take a piece of a black thing (that can not melt) and heat that to 2000K, it will glow with an orange-yellow colour. When you heat it even further (do not try this at home) its glow will be brighter and more white. At 5500K it will have the same colour as average day light and at 10000K the same colour as the iciest blue of the sky.
So, the higher the colour temperature, the cooler it looks!

Candle light has the lowest temperature of all light sources, at around 2000K. Standard tungsten light reaches 2800K, while a halogen spot will reach 3500K. As said, average day light is about 5500K, and this is also the value of most flash lights. Daylight at sunrise and sunset is about 4000K.
At an overcast day, the colours is about 6000-7000K, while the shadow with a blue sky can reach 10000K.

What to do? How does a photographer cope with all this? Can you do anything about this?
Yes, you can. Even a lot. For print film, overexpose up to a stop when the colour is way under 5500K (I know, that is a pain working under sparse tungsten light!). By overexposing, there is enough colour left in the negative, to be able to correct at the printing stage (often a little yellow or blue is desirable for the atmosphere). Fluorescent light is always troublesome, although the newest films cope quite well.
Another option is to put a filter in front of the lens, filtering the abundance of yellow, blue or green. With tungsten light, you need to use a blue filter (the filter is blue - it filters the yellow out!), in the shadow a yellow filter (or strong skylight filter) and a magenta filter under fluorescent light.
This is the only thing you can do with slide film, if you want to avoid the 'real' (but not as we see them) colours. Some slide films are made for the use of tungsten light.

The advent of digital brought new possibilities. Most digital cameras sport an 'auto white balance'. For each shot the camera supposes the kind of light source used and then corrects accordingly.
It is like matrix light metering: in most cases it works, but some subjects are confusing for the camera, like a bright yellow sunshade.
Often the photograph will set the white balance manually - or correct colour in a later stage in Photoshop or the like.

Colour temperature though is not always your enemy. It can be used creatively as well! The yellow cast of tungsten light can stress the atmosphere of home, or a blue cast the cold of snow.
As I always use print film for reportage, I don't mind colour temperature. The lab will take care for me (I overexpose when working in tungsten light!).
Doing landscapes, I accept the fact that the film stresses the real colour of the light, compared to the way we see. Therefore, the time before sunrise will look cooler and at sunlight things might be warmer. What I absolutely won't do is warming up an overcast sky. I have seen too many pictures where this was done too obviously.

Part 2 deals with focussing.

The last part of this article discusses a number of real life situations, in which I explain the way I work in landscape photography. I talk about metering, grey grads, bracketing and handling depth of field.

This article is written by Wim van Velzen, © 2003.
Comments on the article and photographs are welcome!

The landscape photographs shown here and lots more are put in several portfolios! More wedding photos can be found in the wedding galleries.
It is also possible to order landscape prints or to use them editorially or commercially.