You have already used it a few thousand times, but have you considered how a photometer really works? Do you know how to make the most of it? Do you know that there is life beyond that integrated into your camera? Well, if you have never asked yourself these questions or if you did and did not give the answer, I hope that today's article will help you

WHAT IS A PHOTOMETER?

To start, if we want to be perfectionists, when we refer to the photometer , we should talk about an exposure meter , because not all photometers are designed to measure light, there are also designed to measure the color temperature (colorimeter) and not to offer us values of exposition. In contrast, exposure meters, as the name implies, are designed to offer exposure values. The exposure meter (or photometer for the less perfectionist) is designed to measure the intensity of the light of the scene and based on it, it gives us certain exposure values (shutter speed and / or aperture depending on the shooting mode in the that we are working on). Once the terminology is clarified, we will continue as we have been doing throughout life, with the term photometer that, to those of us who had not thought of using colorimeters, is already going well for us

External incident light photometer

WHAT TYPES OF PHOTOMETER EXIST?

There are basically 3 types of photometers: those that measure the reflected light, those that measure the incident light and those that can measure both types of lights.

PHOTOMETER (OR EXPOSURE METER) OF REFLECTED LIGHT

The reflected light photometer or exposure meter measures the light reflected by the people or objects we are photographing. This means that the exposure values ??that the reflected light photometer will offer us will depend on the tones that the objects have , since objects or people with lighter shades reflect more light than objects or people with darker shades . That is, a person of white complexion will give different exposure values ??to a person of darker complexion. The photometer that integrates your camera is one of these . Advantages : It comes integrated in your camera, you cannot forget it, you do not have to buy it, you do not have to load it and, if you get to know its deficiencies well, you can work perfectly with it in most situations. Disadvantages : Since it does not reflect the real light, but the one that reflects things, it is very easy to get lost in situations where we have several light inputs , or in situations where light tones abound (thinking that there is more light than in reality there is and consequently underexposing the scene) or where the dark ones abound (thinking that there is less light than in reality there is and consequently overexposing the scene). That is, the integrated photometer will work well when the tones of the scene approach the medium gray , which is the reflectance tone that is considered standard for a scene, and the one used to work. The more you differ from that tone, the more likely you are to have a wrong exposure. Do you remember that we have ever talked about how snowy landscapes deceive the photometer making you think that there is more light than there really is? And how the value it gives us makes the snow gray instead of white Try to compensate for what you consider an excess of light? Well, that is the fault of the reflected light photometer.

Very light or very dark scenes confuse the reflected light photometer that gives us erroneous exposures if we do not know how to compensate the scene

PHOTOMETER (OR EXPOSURE METER) OF INCIDENT LIGHT

The incident light photometer or exposure meter measures the real light intensity of the scene that affects the subject regardless of the object or person we are photographing and offers exposure values ??accordingly. That is, whether the object is white, black or brown, the exposure value it offers will be the same. Advantages : It is what allows us to really know the light of the scene regardless of the color or tones of it. Exposure values are not perverted and the photometer is not deceived . It also allows us to know the value of the different lights of a scene , what exact difference in diaphragms there are between some lights and others (contrast of lights), and what real light intensity the scene has. Consequently, it is the most accurate of the two. Disadvantages : You have to buy it, load it, learn how to use it, and don't forget it

The incident light photometer allows to know the real light of the scene

HOW DO THEY WORK?

We have already commented that the photometers measure the light (reflected or incident) and provide us with correct exposure values ??in principle for the light of the scene in front of us.

HOW THE REFLECTED LIGHT PHOTOMETER WORKS

In the integrated reflector of the reflected light that our camera has, it is very important to choose correctly the type of measurement necessary for each scene and to know how to interpret the result, since it will depend on the correct or not exposure of the shot.

Matrix or evaluative : Take the exposure references of different points distributed in the frame and propose an average exposure based on the different lights. It works well on most occasions where there is not too much contrast between lights and shadows.
Punctual : Measure exactly at the point we indicate in the scene, focusing on it and avoiding the rest of the lights. It works well when we have a lot of light difference between our center of interest and the rest of the scene.
Partial: Similar to punctual but covers a little more area in the image to assess the exposure.
Weighted to the center: Performs the measurement in the central area of ??the image to which it gives priority, although it takes into account the rest of the lights of the scene.

Also, we must choose a shooting mode . If we choose the manual mode , it is we who must adapt the values ??of the exposure triangle (ISO, shutter speed and aperture of the diaphragm) depending on what the exposure meter integrated in the camera marks. If we choose a priority mode , the photometer or exposure meter will offer us the value of the other variable in the exposure triangle. On the other hand, if we choose the automatic mode, the camera will make the necessary shutter speed, aperture aperture and ISO settings that it deems appropriate. Once the measurement mode and the shooting mode are chosen, we must interpret the measurement offered by the exposure meter, and we do that through the histogram. The histogram helps us know if the exposure is correct. That is to say, not only if we have made the correct adjustments so that the measurement in the photometer is ¨0¨, but also to know if we have been able to interpret the exposure it offers us, finally getting an image according to the scene.

HOW THE INCIDENT LIGHT PHOTOMETER WORKS

As we have said before, the incident light photometer is the one that measures the intensity of light in the real scene, regardless of the tone of everything that appears in it.

We must choose an ISO manually, the same for the camera as for the external photometer.
Then we must choose a shutter speed and indicate it to both the camera and the external photometer.
Once we have the previous settings, we will measure the light from which we want to know the exposure values. The photometer will give us a result in the form of a diaphragm opening . If we vary the ISO or shutter speed, the diaphragm will vary to give us a correct exposure value.

DO I NEED AN EXTERNAL ONE?

Although the incident light photometer (external) is better than the internal reflected light of our camera, the truth is that the latter is usually more than enough to perform in most situations. Before discarding it, the main thing is to learn what are the limitations of our integrated photometer, when it fails and why , and the tricks with which we can solve them. Now, if yours is the portrait or product photography, then I would not hesitate, I would go for one of incident light without thinking too much I hope you found it useful, the key to everything, as always, a lot of practice, many situations, many mistakes and just some theory . The best school is out there waiting for you to take a picture ;-). Ah, but before you go out on your legs for it, remember to share this article with anyone or one you think may be interested or interested. Thank you and see you next time.