We have taken a bit, but here is the sixth installment of our ALTFoto Beginner’s Guide, in which we have been explaining the main controls of our cameras one by one. Today we have to talk about the exposure meters of our cameras, also called light meters, exposure meters, or photometers. There are also much more precise separate camera instruments, but they are for professional use, so let’s put them aside for the time being.
We had already told you before the “triangle of exposure,” formed by the paramount parameters of every camera: ISO sensitivity, the aperture of the diaphragm and shutter speed. Correct exposure will always depend on the balance between the three. It has been like that since photography began, although the way to determine this balance has changed over time. Before any electronic assistance, photographers had to learn by trial and error to calculate the exposure parameters. Later, the manufacturers of films, cameras, and flashes, delivered calculation tables that were printed on the boxes, in small notebooks, and even on the same devices.
With the development of the technique came the first exposure meters, although its use was not extended until they were reduced enough to be included inside the cameras. These new light meters consisted of needles that stayed still or lights that tinkled when a correct exposure was achieved. Later, the graduated scale was introduced in the form of a rule to which we are all accustomed.
What this electronic component does is to collect the information about the ISO, the aperture and the velocity, and calculate if the mixture of them that we have determined will leave the photo exposed correctly, or it will be sub-exposed or over-exposed (with less or more light of the necessary, respectively). The information is shown in this bar with a zero in the center, which goes down to -2 on one side, and goes up to +2 on the other. If this sensor considers that the amount of light that will reach the detector is adequate, the indicator will remain at zero. If there is a lack of light, it will go to the negative side, and if it is left over, it will go to the positive side.
Of course, this indication is programmed according to what some Japanese engineer has determined as correct. There will be occasions in which we will want to sub-expose or over-expose our photo with some artistic purpose. Also, as if to complicate things, the brands do not all do this in the same sense. While the image above shows what a Nikon does, with the positive end to the left, Canon and most other brands put it to the right (which personally seems to be more logical).
Now, how is the exposure meter used? Well, most of our entry-level or intermediate SLRs have two primary modes and some hybrids, depending on the model. Like autofocus, the exposure meter is activated by pressing the shutter-release button halfway. Take out your manuals, which then review the modes:
- Evaluative measurement: Measures the entire surface of the frame, and then adjusts according to what the camera thinks you want to photograph. It does not throw an average of the whole structure, but “scans” it and then chooses what it thinks we want to photograph and measures it.
- Spot Measurement: Measures only the central area, which in most viewers, is marked with a circle. It is the most accurate form of measurement, but to use it correctly, we would have to make the measurement, adjust, and then focus and frame.
- Partial Measurement: It is the same as the spot, but the area in which the measurement is made is a slightly larger circle. In the camera viewfinder, you would reach the top and bottom focus points.
- Average measurement with central preponderance: That the immense name does not frighten them. It is merely an average of the whole frame, but something more important is given to the center.
They can also block the exposure measurement by pressing the button marked with an asterisk (*). This will allow them to measure and adjust the exposure, and then focus and frame without changing the displayed value. If that button is held down to take another photograph, the first measurement will be retained. This is very useful when we want to take several shots of a stage with constant lighting.
In another installment, we will talk about the mode selection wheel in our SLRs, so today, we will only note that below Manual (M), there are options such as Shutter Speed Priority (Tv) or Opening Priority (Av). Since the camera assumes control of the function to which we do not give priority, in these modes, we can correct the work of the camera by changing the exposure value directly on the graduated line, increasing or decreasing points if we think that the quantity of light is not correct.
As you can see, it is a tool that could save us a few test shots, but we must take into account its limitations. To begin, it is not very usual that what we are going to photograph is round, so there will always be some space that will affect the measurement. It does not work very well in situations of high or low light or backlighting. It will not be very precise if the subject is too far away or in movement concerning the light source. I prefer to make a couple of test shots instead of relying on it, but when I’m in situations where the sound of the camera is very striking, it’s worth using.
Note also that if you use the internal flash of the camera, it will emit a burst of flashes to make the measurement, which can be uncomfortable. If it is used with an external flash but communicated with the camera, it may be necessary to adjust in one of the two devices, since it is usually inaccurate. Finally, it does not make sense to use it with a flash without communication with the camera (not TTL), as a “generic” or when using remote triggers, since the measurement does not take into account the power of the flash fired.
With this, we finish our delivery on the exposure meter. If you have any questions left, the comments section is yours.