Almost every modern camera currently being produced has a lightmeter built into it. It's the device that measures the exposure, and allows for accurate adjustments of shutter speed, apertures and ISO settings. Chances are your camera phone even has light measuring capabilities.
So why spend money on a device dedicated to measuring light? There are many reasons, but mainly accuracy and speed. In this tutorial, we'll dive into lightmeters, what kinds there are and what they are capable of.
Lightmeter “Types" or Functions
I hesitated to call this section lightmeter “types" because most lightmeters perform several functions, which originally couldn't be crammed into one meter. Now you can buy meters that do all of the different functions, or sometimes just a few. So here's a rundown of the main types of meter functions. The lightmeter in your camera may even have two or three of these functions.
This function measures the light bouncing off a subject. When using the reflective setting on a meter. You point the sensor at the subject and it will spit out your reading. If you camera has a lightmeter, it is a reflective meter. The problem with this type of meter is that it can be fooled. If something is actually a dark color, the meter will not know and will assume the scene is dark. This can result in overexposing the scene. A small bright area like a face in a dark environment can also fool the meter in the same way. Modern cameras overcome this by using sophisticated software that meter several parts of the scene and then make a guess as to what you're trying to expose.
The incidence reading measures the light falling on to the subject. It eliminates the problem of the subjects tone or color because you don't point the meter at the subject, you point it at the light. In order for this to work, you must place the meter in the same light as the subject. This often requires you to take reading very close to the subject. Reflective metering can be done at a distance. Most basic light meters have incidence and reflective capabilities. This usually involves a light sensor that can be pointed at the subject or covered with a white piece of plastic. Once covered, the meter can be used as a reflective meter. The plastic has a specific density and diffuses the light before it hits the sensor.
As you progress up in quality and cost of lightmeters, this is usually the next function added after the basic functions of reflective and incidence metering. Flash metering is used for determining exposure when using a flash or studio strobe. Normal lightmeters including the ones in cameras, cannot react quickly enough to determine the exposure of split-second pop of a flash. Therefore, a special meter had to be created.
Again, a flash meter isn't something you would buy as a stand-alone unit, it would be a function of a meter with reflective and incidence capabilities as well. I only know of one camera that has a built-in flash meter (a Leica SLR), but this is not to be confused with TTL flash capabilities that modern cameras have. This is a different process in which the camera and flash must communicate electronically.
Spot meters are now built into cameras, but they can also be purchased as stand-alone units or as attachments for other types of meters. A spot meter is a specific type of reflective meter that samples the light from a very narrow area. In the case of a small, bright subject sitting against a dark background, the spot meter could be aimed at and meter only the light coming from the subject. These meters can be very useful and accurate if used correctly.
Color Temperature Metering
This type of metering doesn't exactly deal with exposure, but some high-end meters have a the ability to tell you the “color temperature" of the light you're shooting under. Color temperature deals with white balance. Most DSLRs have a white-balance setting of K or Kelvin that can be adjusted from around 2800K to 8000K (the exact range depends on the camera). Color temperature meters can tell you what number to dial into with one click. 2800K is roughly tungsten or indoor lighting. 5000 to 6000K is daylight and flash is usually a bit higher than daylight.
The Modern Multi-Function Meter
The most common professional/semi-professional meters look very similar. They typically have a digital read out that will display your f/stops, shutter speeds, ISO and various modes. The are equipped with a small white dome diffuser (although these can be changed out for flat diffusers for metering flat surfaces). They have a button to take the reading, and a wheel or set of arrow buttons that will allow you to cycle through possible shutter speed and f/stop combinations. The diffuser is used for incidence readings, and is removed for reflective readings.
How Lightmeters Work
Lightmeters center their exposure readings around one shade, 18% grey. When doing reflective readings, they assume that what they are looking at is 18% grey, which is a light grey color. This is why reflective meter can be fooled. Not everything is 18% grey.
If you take a reflective reading of a black shirt, your meter will not know it black. The resulting reading will be overexposed. If the surface you're metering is a white shirt, your image will be underexposed. That's why incidence readings are so much more accurate, they rely on the white dome to provide the proper shade to expose from. It's not grey, but it's designed to block just enough light from coming through to compensate.
Old-school photographers carried a grey card with them and would place it in whatever light they were working with, and zoom in on it with their camera. That way the reflective meter in their camera could be used more accurately.
Using Your Lightmeter
Take an incidence reading can be a bit tricky at times. Start by deciding what part of the scene you want to be perfectly exposed (all scenes have brighter and darker areas). Then, place your meter in that area. You'll need to decide what direction to point your meter.
Typically you'll want it facing the camera. This will tell you how much light is hitting an area that will be bounce light back to your camera. But occasionally when attempting to achieve dramatic side lighting or rim lighting, you'll want to face the meter toward the light source. This technique is often used in multi-light studio set ups where you want to know how much light one side of a face is getting in relation to the other side.
Shadows and Highlights
As I mentioned above, every scene has darker parts and lighter parts, shadows and highlights, and deciding what to expose for is your choice. You may decide to expose for the highlights and let the shadows become black in your image. Equally, you may decide to expose for the shadows and let the highlights become white in your image. Or you could attempt to expose for a neutrally lit, in-between area, and rely on the dynamic range or your camera to allow the shadows and highlights to show detail.
The Zone System/Meter Averaging
The Zone System, developed by Ansel Adams, is a complex system of determining exposure. The reason it is complex and not used much anymore is that it requires you to know the exact latitude or dynamic range of your film or digital sensor. You need to know the range, and how the range is distributed.
For instance, you might know your camera has 10 stops of dynamic range, but are 8 of those stops below your exposure for the shadows and 2 above for the highlights? Or are there 5 stops above and 5 below? Ansel knew how his film worked and could use the darkest point in his scene and the lightest point to figure how where to place the exposure. The modern way people do this is by using the histogram function on their camera.
Instances Where Handheld Meters Excel
For this tutorial, I'm going to assume that using a lightmeter is faster than taking a series of test shots and checking the back of your digital camera. This could be debated, but for the purposes of these tips, I'm going to assume it's faster. So your two options for determining exposure are: (a) taking an incidence reading with handheld lightmeter, or (b) using your in-camera meter. The following situations would greatly benefit from the use of a handheld meter.
Steady Lighting Situations
One of the best times to use a lightmeter is when you're shooting in situations with consistent, relatively even lighting. The most common of these scenes that I encounter is indoor sports - like basketball or volleyball. Often there are dark backgrounds and bright players. These can fool the reflective lightmeter in your camera occasionally, so an easier prospect would be taking a meter reading, setting your camera on manual and not paying attention to exposure for the rest of your shoot.
Using Vintage Cameras
I've found in my photography journey that there are people who love photography and there are people who love cameras. There are also a lot of people who love both. I happen to fall in the last category. Old, vintage cameras hold a special place in my heart. Not only do I like the craftsmanship and the variety, but I also like the challenge of shooting without the aid of all the modern technology. Needless to say, a lot of these cameras don't have lightmeters. So my handheld meter lets me get great exposures.
Using Off-Camera Flash
Using off-camera flash during studio work or other lighting set-ups is tricky without a lightmeter. As I mentioned, almost every camera has no accurate way to meter for flash without using expensive dedicated flash units. And the top-end studio strobes don't typically allow for automatic metering either. So a lightmeter is often the only way to get exposures nailed down short of guessing with a digital until you get in right.
Night exposures involving lights can be very tricky to expose for with an in-camera meter. The typical amount of black space in such scene tends to cause the camera to overexpose. A handheld meter could be used very close to the subject to achieve an proper exposure. Also, many in-camera meters don't allow shutter speeds beyond a certain time. You can use your lightmeter and the “bulb" setting to make your exposure as long as you need.
Instances To Avoid Using Handheld Meters
This tutorial takes a pretty strong "pro-handheld lightmeter" stance, but as someone who has shot a lot with and without a handheld unit, I know there are plenty of situations when handheld meters are more pain than a pleasure. I've attempted to list a few common ones below.
Variable Light Situations
If you're shooting in situations where the lighting is going to change a lot, then leave the lightmeter in your bag. A good example of this might be a stage show - like a play - where the light literally shifts with each scene.
Another example is when you're moving while photographing something. If you're walking through different rooms in a house or building, wandering in and out of mixed lighting in the woods, or going from inside to outside during a party, then it's better to just rely on your in-camera meter. The handheld will be more work than it's worth.
Using On-Camera Flash
Camera companies have infested millions of dollars to develop dedicated flashes that produce good exposures. Before dedicated flashes, we had thyristors (a sensor on the flash that measured the light). These systems work pretty well. Trying to handle your flash and your meter is too much. While you're shooting, the distance to your subject will probably change, which affects exposure. Also the simple logistics of taking a reading while holding your camera are more trouble than they're worth!
Using Filters or Teleconverters
Let me say upfront that protective filters, UV filters, haze filter and most polarizing filters do not affect your exposure. If you have a filter you keep on the front of your lens, this advice does not apply. But colored filters and IR filters drastically affect exposure, sometimes half a stop, sometime several stops.
Using a lightmeter in this case will mean that you have to know how the filter affects exposure, and be able to compensate for it. Teleconverters have the same affect. Through-the-lens metering (TTL) was a big advancement in camera technology, so make the most of it when using filters or teleconverters.
There aren't many brands producing lightmeters anymore. The most common are Gossen, Sekonic and Polaris, but other brands to look out for are Quantum Instruments, Voigtlander, Wein and Spectra Cine. Konica Minolta made some great, very modern meters, but have now stopped producing them (though you'll still find them on eBay).
Needle Match Incidence/Reflective Meters
A lot of older meters came in this style. Basically, a needle moves to indicate the light level, and you match another needle to that with a dial. Along the outside of the dial you'll find all your possible shutter speed and aperture combinations. Sekonic's Twin Mate (~$110 USD) meter is a modern example. Gossen also produces the Digisix (~$135 USD) that maintains the dials, but also incorporates a digital readout.
Multi-Function Digital Meters
Higher-end meters all look very similar. There is a palm-sized box with controls and a digital display, and on top of that there will be the sensor, typically with a white diffuser dome. I own a Minolta Flash V, which as I mentioned is no longer produced. Gossen produces the DigiPro (~$245 USD), DigiFlash (~$190 USD) and others. Sekonic has their FlashMaster (~$290 USD) and DigitalMaster (~$570 USD) along with some other very expensive meters. Polaris also sells a few models in this style.
Making The Decision
Simple reflective/incidence meters can be for between $100-200 USD, cheaper if you buy used. A multi-function flash meter can cost anywhere from $200-1000 USD. While most meters are cheaper than a good lens, especially if you buy used, it's a decision you'll want to think over.
Try borrowing a meter from a friend to see if it fits into your shooting style, and decide whether it improves your exposures or saves you time. Also keep in mind that most meters are very durable and repairable, so they should last you a long, long time!