You’ve 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’s life beyond the one integrated into your camera? Well, if you’ve never asked yourself these questions. Or if you did and didn’t get the answer, I hope today’s article will help you.
What Is A Photometer?
To begin with, if we want to be perfectionists, when we refer to the photometer. We should talk about exposure meter, because not all photometers are designed to measure light. They are also designed to measure color temperature (colorimeter) and not to give us some exposure values. Exposure meters, on the other hand, as their name implies, are designed to provide exposure values.
The exposure meter (or photometer for the less perfectionist) is designed to measure the intensity of light in the scene. And based on it, gives us certain exposure values (shutter speed and / or diaphragm. Depending on the shooting mode in which we are working).
Once the terminology has been clarified, we will continue as we have been doing all our lives. With the term photometer which, for those of us who had not thought of using colorimeters, is already doing well.
What Types Of Photometers Are There?
Basically there are 3 types of photometers: those that measure reflected light, those that measure 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 offered by the reflected light photometer will depend on the tones of the objects. Since objects or people with lighter tonalities reflect more light than objects or people with darker tonalities.
In other words, a person with fair complexion will give different exposure values to a person with darker complexion.
The Photometer That Integrates Your Camera
Advantages: It comes integrated in your camera, you can’t forget it, you don’t have to buy it. You don’t have to load it and, if you get to know its shortcomings well. You can work perfectly with it in most situations.
Disadvantages: Since it does not reflect the real light, but the light that things reflect. It is very easy to lose it in situations where we have several light entrances. Or in situations where light tones abound, thinking that there is more light. Than there really is and consequently underexposing the scene. Or where there are many dark ones, thinking that there is less light. Than there is in reality and consequently overexposing the scene.
In other words, the integrated photometer will work well when the tones of the scene approach the mid-grey. Which is the reflectance tone that is considered standard for a scene, and the one it uses to work. The more it differs from that tone, the more likely you are to have the wrong exposure.
Do you remember that we’ve ever talked about how snowy landscapes fool the photometer into thinking that there is more light than there really is? And how the value it gives us makes the snow grey instead of white. By trying to compensate for what it considers an excess of light? Well, that’s the fault of the reflected light photometer.
Very clear or very dark scenes confuse the reflected light photometer that gives us erroneous exposures if we do not know how to compensate the scene.
Incident Light Photometer (Or Exposure Meter)
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 gives us exposure values accordingly. In other words, whether the object is white, black or brown, the exposure value it offers us will be the same.
Advantages: It is the one that allows us to really know the light of the scene independently of the color or tonalities of the same one. The exposure values are not perverted in this way and the photometer is not misled.
It also allows us to know the value of the different lights of a scene, what exact difference of diaphragms there are between some lights and others (contrast of lights), and what intensity of real light has the scene.
Consequently, it is the more 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 photometers measure 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 exposure meter of reflected light that has our camera, it is very important to choose correctly the type of measurement needed for each scene and know how to interpret the result, since it will depend on the correct or not exposure of the shot.
Matrix or evaluative: It takes the references of exhibition of different points distributed in the frame and proposes us an average exhibition based on the different lights. It works well most of the time where there is not too much contrast between light and shadow.
Punctual: It measures exactly the point we indicate in the scene, focusing on it and avoiding the rest of 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 includes more of an area in the image to assess the exposure.
Center-weighted: Makes the measurement in the central area of the image to which it gives priority, although it takes into account the rest of the lights in the scene.
Choosing A Shooting Mode
Also, we will have to choose a shooting mode. If we choose the manual mode, we will have to adapt the values of the exposure triangle (ISO, shutter speed and diaphragm aperture) according to the exposure meter integrated in the camera.
If we choose a priority mode, the photometer or exposure meter will give us the value of the other variable of the exposure triangle. On the other hand, if we choose the automatic mode, the camera will make the necessary adjustments of shutter speed, aperture and ISO that it considers opportune.
Once we have chosen the measurement mode and the trigger mode, we must interpret the measurement offered by the exposure meter, and we do this 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 remains at ¨0¨, but to know if we have been able to interpret well the exposure that it offers us, obtaining finally an image according to the scene.
How The Incident Light Photometer Works
As we have already commented before, the incident light photometer is the one that measures the intensity of light of the real scene, independently of the tone that possesses everything that appears in it.
We must choose an ISO manually, the same for the camera as for the external photometer.
Then we have to choose a shutter speed and indicate it both to the camera and to the external photometer.
Once we have the above 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 change the ISO or shutter speed, the diaphragm will change to give us a correct exposure value.
Do I Need An External One?
While 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 throwing it away, the main thing is to learn what the limitations of our integrated photometer are, when it fails and why, and the tricks with which we can solve them.
Now then, if yours is the portrait or the photograph of product, then I would not hesitate, I would go for one of light incident without thinking it too much.
I hope you have found it useful, the key to everything, as always, a lot of practice, many situations, many mistakes and only some theory. The best school is out there waiting for you to go out and photograph it. Ah, but before you go out for it, remember to share this article with anyone you think might be interested. Thank you very much and see you next time.