العوامل التى تؤثر في كفاءة الغالق .. كتاب أسس التصوير الضوئي

Factors affecting shutter efficiency:

The photographer can control some of the factors that affect the efficiency of the shutter, but those that are related to the way the shutter is made are out of his power. Below is a summary of these factors in general.

(a) The estimated exposure time: to clarify this factor, we will assume that the shutter opening movement takes 5 milliseconds and similar time to closing the shutter. This means that the shutter opening and closing movements take 10 milliseconds together, i.e. a second. Here we assume two cases of photography: the first we estimate an exposure for one second - and the other case we estimate an exposure: from the second, so with regard to the first case, we notice that the shutter efficiency becomes 99.5% when exposing for a second, while in the second case, the creator’s efficiency becomes only 75%. We explained this case in (Fig. 63) ...

We conclude from the foregoing that the longer the exposure time, the greater the shutter efficiency. The following shows an excellent shutter efficiency when changing the exposure time
The second exposure becomes shutter efficiency
The percentage of shutter efficiency decreases as its quality decreases. For example, the shutter efficiency in a box camera decreases and reaches 65% when exposing to light for only a second.

(b) The efficiency of the shutter increases as the diaphragm aperture becomes smaller: so it is clear that the opening and closing time of the shutter will be short in front of a narrow aperture, because the distance that the shutter blades travel during the days of the narrow diaphragm aperture will be small, and therefore it does not require a long time to move it in front of this aperture. This factor is not more than a theoretical factor only, but from a practical point of view, controlling the efficiency of the shutter by narrowing the diaphragm aperture is an illogical method, as that. Our goal in increasing the efficiency of the shutter is to get enough light to record a fast movement with a fast creator, so why do we use a narrow aperture diaphragm?!

(C) The smaller the shutter, the smaller the area of ​​the moving blades, which leads to an increase in the efficiency of the shutter for the reason previously mentioned in (B).

Fortunately, most of the newly manufactured types of shutters have excellent efficiency even in some inexpensive types, especially if we balance the current industry with the old types of cameras.