تطبيق القانون العام للعدسات لمعرفة أثر البعد البؤري للعدسة على المسافة.

Apply the general law of lenses to find out the effect of the focal length of a lens on the distance between
Image and lens:

In the previous examples, we estimated that the focal length of the imaging equipment used was only 10 cm. If the focal length of the lens changes by increasing or decreasing from 10, does the lens and image distance change?
No doubt it is changing. This is shown in the following two examples:
(1) We will first assume that the focal length is 50 cm and the object is 50 cm away from the lens.

(2) Secondly, 20 cm by 50 cm.

The image is approximately 33.3 cm away from the lens. If we look at the previous two examples and the example shown (p. 148 in item second), we find that the distance of the object from the lens was 50 cm in the three examples, and the focal length has changed, so we noticed the following:

a) If the focal length of the lens is . The image was formed at a lens distance of 5.5 cm

b) If the focal length of the lens is 10 cm, the image will be formed at a distance of 12.5 cm from the lens.

c) If the focal length of the lens is 20 cm, the image will be formed at a distance of 33.3 cm from the lens.

.. We can decide that the greater the focal length of the photographic lens, the image will gather at a farther distance. So if we imagine a bellows machine with a length of 22 cm and a size of 6 × 9 cm, then the lens “a) will be short in focal length in relation to that machine and its use. The machine becomes more bellows than the three. If we use the second lens “B” (10 cm), the lens has a medium focal length, and the machine becomes a double extension camera. As for the third lens (C), it has a long focal length, and by using it, the machine becomes just a normal bellows camera.