العوامل التي تؤثر في تقدير سرعة الغالق .. كتاب أسس التصوير الضوئي

Factors affecting shutter speed estimation:

Estimating the shutter speed in the camera depends on several considerations, which we will explain. Below :-

(1) The focal length of the lens:

The shutter speed estimate differs when photographing with long focal length lenses if photographing with a short focal length lens. The first case requires faster estimation. To explain this, let us assume that its body is moving at a constant speed in front of a camera whose lens has a long focal length, and the machine has frosted glass at the back to see the image of the moving body. Accordingly, the image of the object appears to us, and you see a relatively large size than if the lens had a short focal length. Due to the large size of the image of the moving object, it is seen as it travels the distance from one side of the frosted glass to the other side in a short period, while if the lens used was of a short focal length, the object would be seen in smaller size and travel the same distance in a longer time than the first case. According to this fact, it is necessary. When photographing, an estimate of a higher shutter speed when photographing with a long focal length lens than if photographing with a short focal length lens (Fig. 83).

A) 1_ The distant moving object appears small on the frosted glass, and thus its movement appears slow, so it does not need a high shutter speed.

b) 2_ The image of the nearest moving object appears larger than the image of the distant object, and therefore its movement appears as if it was fast in relation to the first case, so a higher shutter speed is needed.

h) 3_ If we consider that case B was when photographing with a medium focal length lens, and we consider the case to represent photography with a long focal length lens, then the viewer will see that the image of the object appears larger in the third case than when photographing with a medium focal length lens, and therefore we need a higher shutter speed when Use a long focal length lens.

(2) The distance of the moving object from the camera:

Moving objects close to the camera require a faster shutter speed. Those moving at the same speed and far from the camera, and in order to bring this closer to the mind, we only have to imagine a fast train running one meter away from us and we are looking at it, so can we count the windows of one carriage, for example, or read the writing on it? Undoubtedly, it is difficult to implement. But it is very easy if we stand ten meters away from the train moving at the same speed. And what applies to seeing with the eye applies to seeing with a lens or recording.

The first: an approximate general statement about the speed of movement of some known bodies and its measurement. kilometers per hour.

The second: converting the speed of the moving object into estimates of the shutter speed estimated at a fraction of a second, with linking the speed of the moving object to the distance between it and the camera.