كيف يفكر !! مقياس التعريض .. كتاب التصوير علم وفن

How does he think!! exposure scale?

As for the second type, which is the reflected light meter, which is the type built into the camera, it is what interests us here. Because this type has been calibrated in such a way that it considers any part of the subject that it measures the light on as a medium-light shade of gray, such as the Kodak gray board, which reflects 18% of the light falling on it. If the meter is directed at a subject of many colors or shades, then it collects all the reflected rays, obtains their average, and gives a reading of the exposure, making the average illumination of the whole subject similar to the aforementioned gray board, and this is suitable in most normal cases. But !!

We mentioned before the types of exposure measuring devices and we mentioned the type called the incident light meter. This measures the amount of light that falls on the subject and does not affect the color or degrees of shadows present in the subject. This type gives the best results, except for some previously mentioned defects.

Let us suppose that the scale is directed to a white surface that reflects 90% of the rays falling on it. We will find that the scale gave us an exposure that made this white plate appear

gray in the photo.

. in the picture .

Assuming the opposite, we point the scale at a black surface that does not reflect any rays at all. We will find that the scale gives us a reading that makes the black surface appear gray as well

Therefore, the best measurement is if the scale is directed at the aforementioned Kodak gray board. In this case, we find the colors or shades in the image completely similar to the original subject. all

Usually, if we direct the scale to an ordinary scene that contains all the colors, we find that the reading often gives a good result because the sum of these colors is combined by the scale on
A gray color that reflects about 18% of the light falling on it. Therefore, we find that the scale works in most cases. But there are anomalies! Let us suppose that we are photographing a portrait (face) of a blonde woman with a very white face, and we point the scale at the face. In this case, the picture and the face will appear darker than the truth, and vice versa if we point the scale at a very dark face. And fortunately for us in our region From the world, the wheat face gives almost the same light reflection as the Kodak board, i.e. about 18%, so this method works.

Get rid of all this to: 8 To get the best exposure, it is preferable to measure the reflected light from a gray plate with an 18 reflectance, such as the aforementioned Kodak plate, so that the plate is exposed to the same light falling on the subject and at the same angle. In the absence of the aforementioned plate, the exposure can be measured from the back of the photographer's hand if it is wheat in color, from the inside of his palm if it is very dark. This method is suitable when photographing a distant subject that we cannot approach, for example, a predatory animal at a distance in the midst of standing or very light weeds.

When photographing landscapes, it is preferable to direct the light meter slightly downwards so that it is not affected by a large area of ​​the sky, which gives less exposure than required.
The effect of the subject's lighting contrast on the exposure: We find that the films cannot deal with a high contrast ratio between the least illuminated and the most illuminated regions. We find that positive color films that give colored slides do not accept a contrast in brightness (the least and most illuminated parts of the subject) more than four apertures (16:1 contrast) to give acceptable results. For negative color films, a contrast ratio of twice this is accepted (up to d or 6). Apertures, that is, with a contrast ratio of (32: 1). As for black and white films, they accept a contrast ratio of three times that of the positive color film.

In other words, measuring the least luminous parts of the object should not give an exposure of less than four degrees from the most luminous part (excluding black and white).

Exposure Metering for Low Contrast Subjects:

High (for example, snow. - When photographing a subject with a low contrast, if the overall subject brightness is the beach, sand, fog scenes), we find that the exposure scale gives a reading that shows the image is more list than the truth, and therefore the exposure must be increased by at least a pupillary aperture than what the scale decides, so that the image appears with the same degree of brightness The topic is actually.

When photographing a subject with a low contrast, if the overall brightness of the subject is low (for example, interior scenes without auxiliary lighting), we find that the scale gives readers that make the image lighter or brighter than the reality, and to make the image simulate the reality, it is preferable to give a lower exposure.

Exposure Metering for High Contrast Subjects:

If the contrast ratio exceeds the contrast that the film bears, for example, subjects lit from behind. In this case, the film will not be able to record the bright par
And the dark part at the same time. Therefore, we have to choose which part we want to record on the film in good colors, and make the rest of the image go either completely dark or completely faded.

With regard to positive films (colored slides), paying attention to the lighted parts and making the rest of the image dark gives better results. And vice versa for negative films, where it is preferable to pay attention to the dark part and make the rest of the image faded, but the focus of attention in the subject is visible in the way we want. But if the part is The dark part and the bright part are important... In this case, something must be done to reduce the degree of contrast, such as using a reflector or auxiliary lighting to open the shadow areas.

With practice, you will find that you can estimate the amount of variance in most cases just by looking. There is an easy way to take the correct exposure for the most important part of the subject that works in most cases. For example, if you photograph a person in a room standing in front of a window open to daylight, you will find that if you photograph the image according to the exposure device built into the camera, this person will appear in the resulting image as just a black shadow. (Silhoutte) It has no features at all. To avoid that, all you have to do is approach the person’s face, measure the exposure, keep it, return to your original place, and take the picture. In this case, we will find that the person appeared naturally while the view from the window became dim, and this does no usually matters.