التصوير .. المباديء والمنهاج - ٣ - الكاميرا والعدسة .. وظائف وتقنية العدسات

**Ali Abbass** · 03-22-2023, 01:24 AM

Photography . . Principles and curriculum, the third lesson, the camera and the lens
Lens functionality and technology

After we started in the previous two lessons with a process of comprehensive acquaintance with the camera, let us now explore more about how it works, and study some of its basic contents in more detail, starting with the lens. Light travels in straight lines, and this is an essential feature of the process of forming an image in a camera.
The light from a target flows in a straight line from every point in the target to enter the aperture of the camera down to the film, and this indicates to us that the lens does not have any necessity to form an image on a film, and as we mentioned before, the pinhole camera works without a lens. What happens here is that the light coming from The subject enters a box that prevents the penetration of light through a precise hole, and this light on the film produces an image turned upside down.
From the simple point of view of the process, you find that the image made by the pinhole camera is satisfactory to a significant extent, but it remains of lower quality for two reasons:
1- The image on the film does not come out with the required sharpness and prominence even under the best conditions.
2- Only a small amount of light enters through
The exact hole.
This means that in order to achieve a sufficient exposure, the film needs very long exposure times, sometimes up to hours.
As for the lens, Haneen solves my dilemma, as it works to focus the light rays to produce a sharp image, and then allows the entry of larger amounts of light, which allows for appropriate light exposures within just a tiny fraction of a second. Which allows a much larger amount of light to enter the camera during the same time period.

What is the main function of the lens?
All lenses perform the same basic function. They capture the light that enters the camera and focus it to put a sharp image on the film.

- What is a fixed focus camera ( * )
Some cameras come equipped with a fixed lens.
This lens cannot be removed, replaced, or even moved back and forth, rather it is fixed in place forever. Old Kodak Brownie and some newer (*) instant cameras.
These are called fixed-focus cameras, and you can use them to obtain an image with reasonable protrusion sharpness for all targets that are more than a certain distance away - the maximum distance of two meters.

What is a variable focus camera?
Most cameras come equipped with lenses that can be moved back and forth to focus on a range of varying distances. This is known as a variable focus camera. It can adjust the locations of the lens of varying focus to produce its image with the sharpest prominence of targets located at any distance from nihilism that exceeds its minimum focus distance. An example of this is that you move the lens forward or backward. You can adjust it to focus on targets with different dimensions.

- What is an interchangeable lens camera ( * )
Some cameras are equipped with lenses that can be removed so that other lenses can be installed in their place. These are known as interchangeable lens cameras, and almost all of them are variable focus cameras as well.
They are the most versatile cameras as long as they allow you to use different lenses to carry out different tasks, and focus each lens to obtain the largest possible prominence from varying distances. Cameras of this type include most of the more expensive models.

But why would you want to change lenses? What can one lens do that another can't?
Lenses have two basic features that determine the type of image that these lenses transmit to your film, one of which is the speed of the lens. The second is the focal length or aperture stops. F...
Let's find out what all this means.

Lens speed
What is the speed of the lens? ...
The speed of the lens refers to the amount of light that a particular lens can transmit in a certain period of time. The lens that transmits a lot of light is known as a fast lens, while the one that transmits an amount of light less than that at a noticeable rate is known as the slow lens.

First, you should not confuse these two expressions, the fast lens and the slow lens, with the ability to capture fast moving subjects, because the expression is fast. When a lens is called, it has only a relatively small relationship with the ability of this lens to stop movement, while this expression relates to the amount of light that this lens transmits in a certain period of time.

How do we determine the speed of a lens? ...
The speed of a particular lens is not determined by the number. F, for its widest opening. If the widest aperture of a particular lens is set at f / 2, for example, then this lens is referred to as an f / 2 lens.
The lower the number. The greater the amount of light transmitted or the faster the lens, in other words.
A lens with a maximum aperture of f/1.4 is called an f/1.4 lens. This is faster than the f/2 lens. While the f / 2 lens is faster than the f / 2 lens. And so on.
Look at your camera lens now. What is its maximum aperture, which is the smallest F / number in it? ... This is the speed of your lens.
An important point to remember is that any lens placed at a certain f/f number must transmit the same amount of light as any other lens placed at the same f/f number. Similarly, when two different lenses are placed at f/2.8, they must allow the amount of light to enter. It's the same way the movie gets there, other things being equal.

**Ali Abbass** · 03-22-2023, 01:26 AM

What are the advantages and disadvantages of a fast lens? ..
What is the reason for the great interest in the fast lens? ..
The reason is very simple, it allows you to take the picture in light conditions that are too weak for a slower lens to suffice.
Let's say you have two cameras, one with an f/2 lens; And the other with an f / 4 lens and you want to take an indoor shot under weak light that reflects your light meter - which we will discuss later. And you discover that you open your lens to f / 2. In 1/30 of a second you can capture just enough light to get a properly exposed photo.
You can capture the scene with an f/2 lens at 1/30 of a second and cannot successfully capture it at 1/30
A second with an f / 4 lens, as long as the maximum amount of light that this lens can transmit to the film is not enough to make a proper negative exposure, the meaning of this faster lens gives you a wider range of lighting conditions with which you can capture without adding artificial light.
But why doesn't everyone always use the fastest lens available? ... The reason is partly due to the cost, as the faster lens costs more than another of equal quality, but it is slower, in addition to the fact that the faster lens is usually larger and heavier.
In addition to this, due to the technical complications required to make a fast lens, it often happens that the slower lens produces an image characterized by sharper prominence at its maximum aperture.
And for most light conditions. Perhaps the eta lens may prove to be even better than another faster one. For example, if you want to shoot outside in a well-lit day, your light meter may ask you to set your aperture at f / 8 in this case.
For the previous example, both the f/4 and f/2 lenses should be downgraded to f/8 and the fact that the f/2 lens is faster wide open remains f/8 regardless of the maximum aperture of the lens.
This means that the two lenses allow the same amount of light to enter at f8, but since the fast lenses are typically designed to be at their best while they are wide open, it becomes that at f/8 the slower lens may happen to produce an image with sharper prominence than sharpness. The projection achieved by the faster lens with the same aperture.

You can use faster and more sensitive film - this means, in other words, a film that needs less light to produce a good quality image on the photosensitive layer.
long, until an image is emitted and then you can add artificial lights to the scene with light flood lamps, light flash lamps, or electronic flash.
The important point at the present time is that while you are buying a camera, there may not be a justification for the additional costs and largeness if the conditions in which you will work do not usually require a very fast lens. As you progress through this seminar, it will help you to determine your needs precisely.

- What is the « aperture » stop focal length?
The speed of the lens is related to the ability of this lens to transmit light. If you are not interested in the maximum amount of light that the lens can enter, we need a way to reduce the light that infiltrates through the lens, and this we do by changing the size of the aperture in the lens. As for the aperture, it is the entry hole. The modernity of the diaphragm is as follows.
The diaphragm is like a faucet if we open it wide. Allows a large stream of light to enter. If we narrow its opening, a small stream of light is allowed to enter.
What are the pauses? F. ? ..
The aperture scale is indicated by a number called f/number like f/102... Look at your camera now - it will f/8...f 16. The smaller the F-number, the wider the lens aperture. On the lens, you will find a series of F-number locations called stops, so write them sequentially from the lowest number to the largest on the following lines (4).
Now you know that as the numbers get bigger, the aperture gets smaller. Note this by looking at the pupil of the diaphragm of your lens as you move it from one location to the next. And while you do this, note also that you can set your aperture at any point between the f / f stops specified on your camera, because the diaphragm works in a smooth continuous manner, which makes
Thus, it gives you an unlimited number of lens slots behind the cover in some cameras, from which you can choose what you want.
This comes with the diaphragm, where it is usually closed except for the actual capture, and in order to see the diaphragm, you will have to open the shutter and keep it open by setting the shutter speed at B or T.

- What is the relationship between pauses / f? ...
Why do you find the exact numbers of the /q pause you wrote moments ago etched on your camera instead of any other combination of numbers? ...
The reason is that these are “combination” numbers.. By knowing them and using them, you can adjust your exposure
with more ease. Here's how it happens.
By opening one full f/stop, you double the amount of light entering the camera, other things being equal.
As for shutting off a full pause / q, it cuts that light into half, in case other things are equal as well.
It's a simple yet vital truth.
It means that f/4 lets in twice as much light as f/5,6 and f5,6 lets in twice as much light as f/8. F/8 lets in twice as much light as F/8. An F/8 allows twice as much light in as an F/11, and so on.
Either full string of numbers /q
They are respectively:
F / 1 - F / 1,4 - F / 2 - F / 2,8 - F / 4 - F / 5,6 - F 8 - F / 11 - F / 16 - F / 22 - F / 32 - F / 44 - F / 64.

Look at the list you made for your lens, most likely it follows a clip taken from somewhere in the middle of the chain above -
For example, it is f/2.8-4-5.6-8-11-16, and in this case the lens is known as a f/208 lens as long as this is its widest aperture.
You should get used to these /v pauses. Do you know the reason why / 8 allows the entry of four times the amount of light that is entered by q / 16 .. or the reason is that q / 11 allows the entry of 1/8 (eighth) of the amount of light that is entered by q / 4? .. If you don't know that yet, go back to reading this passage again before you continue.
It should be noted that your camera may contain a f / stop that does not exist in the series mentioned above, f / 18, for example, or f / 19, or f / 35. If this is the case, know that f / 1.8 allows an amount of light to enter Its interference is f / 2 with an increase of about a third, and that f / 3.5 allows the entry of an amount of light equal to what it enters f / 4 with an increase of about a quarter. Almost the same. Your knowledge of the complete series of F / stops from F / 1 to F / 64 will have a valuable impact on your future work. If this series is not already familiar to you, study it now, and let it stick in your memory.
One of the simple tricks that help you save it is your observation that with some minor modifications. Each pause / f is complete, and it is double the pause of f that preceded it by two pauses, as follows

1 - 2 - 4 - 8 - 16 - 32 - 64 - 1,4 - 2,8 - 5,6 - 11 - 22 - 44 .

Changing the aperture changes the amount of light that enters the camera, and this affects the image that ends up with it, and with this subject a series of photos were all taken on the same film and under similar conditions and the lighting remained the same and the shutter speed remained the same. The only thing that changed was the aperture. Thus came the results that can be studied and applied.

Next lesson: Lenses and focal lengths

التصوير .. المباديء والمنهاج - ٣ - الكاميرا والعدسة .. وظائف وتقنية العدسات

التصوير .. المباديء والمنهاج - ٣ - الكاميرا والعدسة .. وظائف وتقنية العدسات

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