This is an article by guest author Enrique Pandolfi in which he introduces you to the gray card (gray card, gray card or any of the names by which it is known) so that your photos have the color they should have 😉 .
What is the “gray card” or “Grey 18%” used for?
Has it ever happened to you that after photographing an object that you see white, it turns out looking gray on the screen of your camera (or after developing)? Likewise, who has not experienced almost black areas in a scene, turning out to be gray when looking at the photograph? And the worst thing is that all this can happen to us despite the care in correctly adjusting the white balance and setting the photometer (or incident light exposure meter) of the camera perfectly at zero.
So, how can this phenomenon be explained and how can it be solved? If you want an answer and a solution, I invite you to continue reading.
The aforementioned situation is explained by the difference that exists between: measuring the incident light or measure the reflected light by the object we are photographing.
To understand it more easily, this effect is the same that occurs when we wear light clothing on hot days, ensuring that the sun’s rays reflect a lot and not feel less overwhelmed by the heat. On the contrary, if we were to wear dark or black clothes, we would receive the impact of absorb all the heat in our clothing.
If we understand this idea we can transfer it to our photographic experience. When you measure the light of an object in a given scene, the camera’s built-in light meter actually measures the reflected light for the object in question. Therefore, it will depend on the object’s color’s ability to absorb more or less light, and this is what could distort, apparently, the measurement of the photometer.
What you should know for a correct exposure (photometer at zero) is the incident light in the scene (or object) and not the reflected light, which is what the camera has the ability to measure. This is the key.
How to solve it?
Then…. how can it be fixed, if the camera is not completely capable of doing it by itself?
Photometer
The most expensive solution is to buy an external exposure meter. This device must be exposed to light incident on the scene (or object) and will do all the worked telling you what are the exact values ​​of diaphragm opening (f/), speed and ISO, which you must adjust in the camera to achieve a correct exposure.
It is very convenient to pay attention in these cases since, if you move the object from position, the incident light will probably no longer be the same (as in the previous shot), so you will have to measure the light again with the photometer and adjust to the new recorded values. Conversely, if the subject remains still, you can move as much as you like to get the right angle without having to readjust the initial parameters (aperture, shutter speed and ISO).
gray letter
But, according to my experience, we do not always have the necessary money to purchase this photographic accessory. Which, by the way, is quite expensive. This is where our gray chart (or photometric exposure chart that reflects 18% of light) appears. As the photo shows, it is nothing more than a piece of gray cardboard. Although now you can also find flexible and different materials. It is an accessory that can be obtained for very little money in any photography house and that will fulfill the function of an external exposure meter to evaluate the light of the scene (or object).
How does it work for these cases? We are going to summarize it by saying that the value of 18% of light reflected on a surface is just what our optical system decodes as a color between black and white (that is, the light situation does not matter, with the gray card we will obtain an average of 18 % that the camera’s light meter would interpret as the correct exposure setting).
How to use the gray card?
Place the chart in the place where you want to measure the light of the scene (or object) and make the exposure adjustment of your camera (in the usual mode that you choose for the measurement). Now, take the values ​​of aperture, shutter speed and ISO until the light meter indicates zero.
This is an economical, easy to transport and essential tool for an adequate exposure of your photographs. I hope you find it useful to solve the difficulties described at the beginning of the article.
This is an article by Enrique Pandolfi, reader of the Photographer’s Blog who gives us his grain of sand.
If you also want to participate as a guest author, click here.
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