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Exposure meters principles and types

Exposure meters of all kinds remain necessary, despite the conversion of most modern cameras to the principle of automatic exposure, as there are several topics that work on deception and fallacy, and we must take note of the types of meters required for each circumstance of the issue of proper exposure of importance in the success or failure of our photographic business.

To get the best photographic results a must
In order to ensure a correct and accurate exposure.. And both the “F” stop and the shutter speed must be equipped with the exact form that suits the amount of light available, and this necessarily means that we have to know the amount of light in order to reach a correct exposure.

In the beginnings of photography, there were no means of measuring light, and photographers were satisfied with their speculations, relying on experiments and expertise to estimate the amounts of light, prepare the stance, and the speed of the sling, according to this estimate. They rely on their expertise in this field. However, in complex cases and when working with color films, they will find themselves forced to use the photoexpression counter * to reach more accurate results.

Separate counters
Thus, light counters arose initially, separate from cameras that are held by the hand and are included with the camera. These counters are of various types, implicit or separate, depending on a fixed fact in their work, as they include one of the compounds that are affected in one way or another by exposure to light, these compounds - gallium. Selenium and cadmium, silicon -

When the light falls on one of these compounds such as selenium, for example, a weak electric current is created, the loss of which is equal to the strength of the light.. The stronger the incident light, the more the strength of the resulting current doubles. By measuring the emerging current, it becomes possible to estimate the strength of this light. Other types of these compounds change their resistance to electricity with the influence of light. By passing an electric current within the cells made of these compounds, it becomes possible to measure the amount of light by simply expressing the change in resistance.
Although selenium cells do not need a battery to charge them with energy, their use is rare compared to other varieties, due to the need for a wide area to become effective, and they are relatively insufficiently sensitive to light levels.
Only the separate counters that hold hands still depend mostly on selenium cells. Because distinguishing them over a large area is possible, as there is no need to economize on an issue, as the scales are urgently the case with the implicit counters. Thus, it can be emphasized that other types of compounds are more useful to designers of more accurate and complex cameras, because they are characterized by sensitivity to weak optical levels, local silicon, for example. And within a small area that is clearly affected by exposure to moonlight, and thus can be included in an effective meter
Inside the body of a single-lens reflex camera with ease.

Implicit counters

There are some implicit counters that depend on selenium, within some large and cheap cameras.
In the old implicit units, the meter records the light coming through a hole on the front of the camera, and on the basis of reading this meter, the photographer adjusts the camera controls in a manner commensurate with the light conditions. Through the image of the subject, not from the subject itself, and the benefit of this matter is in measuring the light through the camera lens, and therefore if the viewing angle is a guest in the lens, then this is the angle in the meter.

The first counters worked through the (TTL) lens to read the average of the team on the focus screen. As for the modern, more accurate and complex cameras, they measure the brightness in the center of the image only, or emphasize the center more than stressing it on the edges, in order to reach more accurate results.
The disadvantage of the implicit counters is that it borrows all subjects as a typical subject, that is, it is a subject characterized by normal color contrast - a little dark, a little bright, and some in between dark and bright - and here the main point of interest is the center point, provided that it is not strongly lit from the background or middle.
So, with topics different from this reality, i.e. non-typical topics, the implicit counters are often mistaken in their readings. And if the photographer did not intend to use his experience and estimates for the required reading

The audio exposure will be under or overexposure. From here, we find that some of those who have digital light meters in their cameras use a separate meter to get accurate readings in circumstances where the (TTL) meters are prone to error.

- Local counters - Spot -

By using a small light-sensing cell with a specific arrangement of lenses, a photometer can be formed that measures the brilliance of only a small part of the subject. The subject through the viewfinder, to show the concerned area in the form of a small circle within a wide frame.
And because these meters measure the light reflected from a small area, they are ideal for conditions where the most important part of the subject is lit by intense luster or is very far away.. An example of this is the measurement of the spot of light falling on an actor in the center of the stage by a photographer sitting in the middle of the hall on his seat private .

Incandescent light counters

The implicit meter errors are often caused by measuring the light when it is reflected from the subject, which leads to its deception by subjects with different color contrasts. The aforementioned counter (TTL) works well when the subject is gray in color, but with the black subject it will give more exposure, as the black subject physically appears in the final image, but with the white subject, the opposite happens, i.e. underexposed, on the basis directed to a gray subject also from here And when I work with a film of color transparency - in particular - a more accurate exposure reading is obtained by measuring the light incident on the subject, not reflected from it.
This is the principle upon which the incident light counters are based. * These counters are distinguished by a white plastic that covers the light-sensing cell. Instead of placing the meter next to the camera and directing it towards the subject, you stand next to the subject and direct the counter towards the camera. This means that the incident light counters give the same results no matter what. The color contrast of the subject and knowing that it is very useful with the presence of film - transparency, colored inside the camera, it is also of high value when measuring the light for copies.

As we mentioned, thanks to the plastic dome that can be placed and removed as desired, these counters turn into counters for the incident light - with the dome present - and for the reflected light - when the dome is removed - and we can then control this matter according to the subjects that you work on photographing.