Inside this issue
Using Light Meters
Amateur Photographer who plays with big cameras and film when in between digital photographs.
In the last episode of our metering series, we talked about what type of meters were available (excluding in camera matrix style metering) and how they work. We also covered the basic ideas behind the subject brightness range.
In summary we have spot meters that take a reading of a specific small area of a scene and incident meters that measure the light falling on a scene. The typical subject brightness range (SBR) of a non reflective scene is from -3 to +3 stops.
Now we’ll take a look at how you would use each type of meter to measure the brightness of a scene and how you would choose an aperture and shutter speed based on this.
Firstly, to make this simpler, we’re going to work in EVs (actually LV but we’ll explain that in a bit).
An EV translates as an ‘exposure value’. It’s an arbitrary unit that is 1 when the aperture is 1, the shutter speed is 1 and the ISO is 100. Real EV values vary when you change the ISO but most light meters that read EV’s don’t change when you change the ISO and for correctness we should say that these are measuring LV (light value). The advantage of LV is that if you have a given value of LV it defines the intensity of light and hence becomes a single value that you can remember in the future (after some time working with meters you’ll know what the LV of a white cloud is on a sunny day for instance).
NB: Modern light meters like the Sekonic use EV instead of LV. If you want to work in EV then change the ISO to 100.
OK, now we know we’re working with absolute light levels in units of one f/stop we can look at how each type of light meter works.
The incident meter should be considered your go to meter for typical photography. It is more likely to produce a well exposed picture than any other form of metering. This is because, as we have learned earlier, the typical brightness range of a non-reflective subject is +/- 3 stops and nearly all film is capable of recording +/- 3 stops of light; hence if an incident meter is placed next to a non-reflective object and in the light that that object is illuminated by, then you will get an exposure reading that will give good exposure from shadows to highlights.
The problem starts when your subject matter is sitting in a different light than that in which you are currently standing. This is why you should walk up to the subject and place the incident meter as close as possible to the subject with the meter pointing back at the camera. This is what you will typically see in most portrait photography - the photographer will walk up to the model and place the meter in front of their face with the meter pointing back at the camera.
In many situations you have a problem that you can’t walk up to the subject and perhaps the subject is being lit by point light source or sources. Let’s take these one at a time
You can’t walk up to the subject
In this case you have a couple of options.
If your subject in the distance is in the same light as you
You can just take an incident reading where you are.
If your subject is in direct sunlight
Then find a bit of direct sunlight and place your incident meter in it (pointing back at the camera)
If your subject is in the shade
You can just cast a shadow on your meter (try to cast a shadow with your hand at a distance from the meter - we’ll come back to why in a bit). This should work as long as the type of shade is the same.
How do I know if the type of shade is the same?
Well, you need to work out in your head where the majority of the light is coming from.
For instance, on a cloudy day, the main light will be coming from all parts of the sky and so you need to make sure your light meter sees all of the sky (apart from the direct light).
However on a blue sky day in desert canyons (for a somewhat forced example) the majority of light for shaded areas is probably reflected from the ground around you; the blue sky won’t be contributing much at all.
Your subject is lit by point light source(s)
This could be problematical, especially if the the lighting is point source based which falls in intensity as you get further away. Your best bet is to find a light nearby which you can place your meter under to get close to the values. This is where you could do with a spot meter..
The biggest problem with incident meters
As landscape photographers, the biggest issue with incident metering is that you can’t take a reading of the sky (or part thereof). There are heuristic workarounds for this but they’re not simple and will be part of a future instalment.
In reality, if you’re taking pictures that include the sky and you want to be accurate then you really need a spot meter.
NB If you’re using colour negative film, you probably don’t need to worry about the sky readings as colour negative has such a large dynamic range. As long as you get the shadows right you should be fine and so it’s best to take a shadow reading. If you’re worried about underexposing, shade your incident meter and use that reading.
The Spot Meter
The spot meter is undoubtedly the best way to take readings of scene luminosity. A one degree meter can accurately place tones throughout the range of your scene and you can look around for the darkest and lightest parts of your scene and place them according to your film or sensor.