تحريك آلة التصوير في اتجاه حركة الجسم Panning .. كتاب آلة التصوير

Moving the camera in the direction of body movement Panning:

Some photographers follow the method of moving the camera in the direction of the movement of the body during film exposure when the maximum shutter speed of the camera is less than the appropriate limit to record the fast movement of the body, as the rate of movement of the body decreases if the camera moves in the same direction. Let us take an example of this with a car that is running at a speed of one hundred kilometers per hour. There is no doubt that this movement will seem very fast to a person standing still in the street, but it will not appear so if the person is riding another car that has a speed of 60 kilometers per hour, for example, and is traveling in the same direction. direction. So if we assume that this person wants to photograph the car in the first case (while he is standing in the street), then he needs to estimate a very high shutter speed, which we may estimate at 1/500 of a second, for example. In the second case, it will require a shutter speed much lower than the previous one (for example, 1/200 of a second). Perhaps the previous examples have shown the effect of moving the camera while exposing the film in the direction of the moving body, as it would be necessary for the movement of the camera to be caused by the cameraman’s cup in another vehicle, or as a result of moving it by hand. Originally, which is located behind or in front of the moving body, it is shaky in the picture (Fig. 170) due to its stability with respect to the moving camera. This method is considered one of the means of suggesting movement in the image.

It is easy to follow the previous method even when photographing with the simplest machines (such as the box machine), by pressing the camera on the body of the photographer and holding it firmly, while following the movement of the body before shooting, and during it, the photographer rotates in a manner that corresponds to the speed of movement. That is, it requires the following:

1- The camera should move in the direction of the movement of the body and its balance.

2- With a speed appropriate to the movement of the body.

3- The movement of the body should be horizontal with respect to the axis of the photographic lens.

Notes on estimating shutter speed:

1- The shutter speed may not be less than 1/25 of a second in the case of holding the camera by hand, as it is very likely that the hand will shake, which will result in the image shaking. pregnant .

2- If we are confused when estimating the speed, it is better that we tend to the higher speed, for example if we estimate a shutter speed between 1/500 or 1/250 of a second to photograph a moving object, in order to prevent error it is better
The speed should be 1/250 of a second.

Calculating the speed of objects from measuring the range of movement of their image on the film:

In many different purposes in the modern era, we sometimes ask to know the speed of very fast objects, such as (missiles - planes - cars - racing horses. Sports movements ... etc.)

It is easy to calculate the speed of movement of these bodies from measuring the extent of the movement of its image on the film (ie the extent of the image's vibration during the exposure time that we estimated), because if the body is moving, then its image must move on the film as well. And the range of movement of the image increases whenever the speed of movement of the body increases in nature (and the range of movement of the image is also affected by other factors previously referred to on p. 302). .

Unless the exposure speed is appropriate to the speed of the body's movement, the image will be shaky, and for this reason we always intend to increase the exposure speed, i.e. the shutter speed, to what is necessary for the speed of the body's movement, or at least estimate the appropriate exposure for its movement.

However, (in our case) we will deliberately shift the speed of the exposure speed from the appropriate amount, in order for the image of the moving body to be intentionally shaken, as it is possible to study the movement of the image on the film (i.e. the extent of its vibration) to estimate the speed of movement of objects. Here is an example of how to calculate movement speed:

Example :

A moving object four meters long, we photographed it with a camera that is a hundred meters away from it, so what is the speed of its movement (or flight) if we knew that the lens had a focal length of 10 cm, and that the exposure speed was only 1/100 of a second?

the answer :

To find out the speed, follow these steps:

First: calculating the magnification (1):

Magnification t = focal length of the lens (z) at the distance of the object from the lens (x) = 10 / 10000 = 1 / 1000 cm

Second: Calculating the length of the image of the body if it was fixed:

Body image length = body length in nature x magnification
= 400 cm x 1/1000 = 4, 0 cm = 4 millimeters

Third: Calculating the length of the shaken image:

Where the exposure speed (1/100 of a second) is less than the appropriate limit for freezing motion, so the image of the object must be shaky on the film (i.e. its image is not sharp and more elongated than its image if it was not moving). It is possible to measure the elongation of its image by means of Extremely accurate microscopic measuring instruments. Suppose that it was shown by microscopic measurement that the length of the shaken image = 12 millimeters.

Fourth: Calculating the amount of movement of the image of the body on the film during the exposure period:

The amount of motion of the body image = the length of the vibrating image - the length of the image of the body if it was not moving.

= 12 millimeters - 4 millimeters = 8 millimeters (Fig. 171).

Fifth: Calculating the speed of movement of the body:

... the distance traveled by the body during the duration of the exposure = movement speed x exposure speed.

... the distance traveled by the image of the object during the duration of the exposure = speed of movement of the object x exposure speed x magnification ratio

... the distance traveled by the image of the object during the exposure time = the amount of vibration of the image

The speed of movement of the object = the extent of the image flickering over the exposure speed x the magnification in millimeters

= 8 millimeters over 1/100 of a second x 1/1000
= 8 x 100 / 1 x 1,000 / 1
= 800,000 millimeters per second
= 800 meters per second
= 2880 kilometers per hour

And since the accuracy of the results of such experiments depends on the shutter efficiency (see p. 280), so the shutter must be extremely high. Relative when using a Focal plane Shutter (see p. 289, Fig. 160) - so such experiments must be carried out by a machine equipped with a diaphragm shutter.