فن التصوير .. المباديء والمنهاج -٩- التركيز وعمق المجال قوانين ، أنظمة ومقاييس

**Ali Abbass** · 04-19-2023, 01:24 AM

art of photography . . Principles and Curriculum Lesson IX Focus and depth of field Laws, systems and standards

Focusing is adjusting the distance between the lens and the film to produce a specific image with greater accuracy... But it always happens that beginners often make a mistake in estimating the results of their work, especially after enlarging the images that they think are sharp and well-focused, but they soon appear distorted on an enlarged print. We can see many examples of this - including what is attached to this topic.
From here, you should get to know the focus system in your camera well, as well as study this lesson to make sure that you are able to obtain an accurate focus on an ongoing basis.

Using the focus scale:
We pointed out that some medium-priced cameras have a fixed focus. It is true that targets that are only a few feet away from the camera cannot be brought into focus, but everything that exceeds five or six feet will be relatively sharp. This is convenient, but it does not allow you to adjust the focus and limits your photography.
This means that your camera should feature an adjustable focus. This is regulated by moving the lens inward or outward by one system or another.

The simplest method is the focus scale or distance scale that you are likely to find on your camera or on the lens. Such a scale has markings indicating the distance from the lens to the subject, usually in feet - and sometimes inches - and often in meters. As for using such a method, it is simply to measure and estimate the distance from the lens to the subject, then put this distance on your focus scale, and when you do that, you will automatically move the lens inward or outward in order to produce a sharp image of your subject on the film. If the subject is 15 feet away, all you do is set your focus meter - your subject is sharply focused.

Look at the focus scale on your camera carefully, and as you can see, the distance indicators go from the closest distance that your lens can focus on, to the distance of infinity, everything that exceeds it is in focus. Infinity is often indicated on your lens by the symbol ∞. Whenever you want to bring distant subjects into focus, it is enough to set your scale on infinity.
However, using the concentration scale alone is not very appropriate. You may not be able to measure the distance to your subject easily, and your estimation of the distance may not be accurate, hence most good cameras include a faster and more convenient additional focus method - either a grained glass system, a field-finder system, or a combination of the two.
Let's explore the three systems:

Concentration of fine-grained glass:

This is the system in place in single-lens reflex cameras (SLR), dual-lens reflex cameras (TLR), and larger viewing cameras. You look at the image through the viewfinder. And with most SLR cameras, it's enough to turn a ring on the lens barrel until your image is precisely defined in the viewfinder, and that's all there is to it. And with a TLR camera and a View Camera. Adjust the focus knob or move the lens inward or outward to accomplish the same thing.

It's a quick and easy process:
When you focus, this means that you are making the most accurate capture. The focus adjuster moved towards one side, and watched as the image became more and more accurate until it reached the point of maximum accuracy, after which it became blurred again. Then, you work carefully to move the adjuster in the opposite direction - back and forth - until you reach the point of maximum sharpness. At this point, your subject should come into perfect focus.
What do you do if your subject has a depth of three dimensions, so that part of them is in focus and part is out of focus...? What part do you focus on? ... The answer is very simple, you focus on the most important part, and the same is that if you are going to take a picture of a face - in black and white or in color - focus on the eyes.

Focus area:
In cameras that use an optical viewfinder system - such as Leica - a field-finder system is usually used as well, and the most common system relates to a composite image, so when the image is out of focus, you see two adjacent images of the subject. This is usually the lens cylinder is paired with the field limiter, so that when you turn the cylinder, you bring the two images closer to each other more and more, then when the subject becomes perfectly focused, the two images blend together so that they turn into one. Another type of field-finder system is the split-image system (*) found in many SLR cameras.

Here the focus screen appears divided vertically from the middle. As you focus, the two halves line up, getting closer and closer, until they merge into one image.

Mixed focus:
Most SLR cameras have a split-image fieldfinder as well as a grained glass focus. Usually, the divided image appears within a circle in the center of the viewfinder. This, and with a blending system, you can choose either the glass granule or the split image to focus on depending on the conditions.

It may be easier to use the rangefinder in dim light; While the grained glass image is easier to work with in bright light conditions, when using the split image as a means of focusing, usually try to find a well-defined line on the subject you are focusing on - a wire, a fence post. Column, door edge, appearance
The side of the nose - by focusing on this line, you can quickly and accurately bring the whole image into focus.

Notes about focus:
A - The closer you get to the subject, the more important the focus accuracy becomes. When the subject is twenty feet away, your focus may deviate by a few feet, but you get an image with reasonable protrusion sharpness. But if your subject is three feet away, even an inch of deviation can throw the image significantly out of focus.

B- When you use a SLR camera and you want to get a perfect focus for a close subject, keep focusing until you see an image with the sharpest possible protrusion in the viewfinder. More precisely, press the shutter button.

A - If you focus on a face in dim light. If you cannot find any prominent line to focus on, ask your subject to raise a finger in front of their face, and then use the split image of the finger in the field finder as your guide to focus.

D - If you are shooting a moving target coming towards you or away from you, choose and focus in advance on a point where you want to take the picture. And keep the subject within the viewfinder while this subject is advancing or moving away from you. This is to be captured with a camera (SLR) when the subject appears in maximum sharpness with its prominence. It is captured with a field finder camera when its two images meet together.
E - When you capture distant scenes, it is sufficient to prepare your focus to infinity.

Depth of field:
When a target is in focus, everything from a certain distance in front of the target to a certain distance behind the target will be focused with reasonable accuracy as well. This distance, which will be centered with reasonable precision from front to back, is called depth of field.
Look at this active movement photo. Notice how precisely the players are in focus, but the ground in the foreground and the audience in the background are both out of focus. If you took this picture with a great depth of field - with everything in focus from front to back - imagine how obstructed it would be because our squinting attention to the players would be turbulent with a sea of obvious faces that You will surround these players in the audience.
Does this mean you have to always work with a shallow depth of field...? No, never. If you meant that in the image of railway lines that converge at the horizon, for example - you will give a sense of continuous distance - you seek the largest possible depth of field in your image and with a precise focus that everything enjoys, near or far.
Thus, the depth of field that you adopt in a particular photo depends on what you are trying to convey to the viewers of your photo. The important point here is that you have the freedom to choose. You can control the depth of field in your photo when you take it. And your intelligent choice of depth of field is an important creative tool.

- Depth of field control - Aperture:
One way to control the depth of field is based on your choice of aperture. Compare these two images and try to figure out which one has the greater depth of field, the one taken at f/2.8 or the one taken at f/16. It is clear that the photo taken at f/16 has a much greater depth of field than the one with which the photo was taken at f/2.8.
So the narrower the aperture - the larger the f/number - the greater the depth of field. The wider the aperture - the smaller the f/number - the shallower the depth of field.
If you want to combine a group of shapes and get a clear protrusion sharpness, we will use an aperture of f / 16, so all the shapes come with a full aperture of the shapes, and in the opposite case, that is, when using f / 3,5, you will get the shape in the foreground of the image with full clarity, while the rest of the other shapes are outside. About focus - If changing the aperture of the lens also leads to a change in the depth of field.

- Control the depth of field - the distance.
To control the depth of field, we have to deviate a little from the topic. For example, if we take a picture of four or five columns erect at f / 4 and focus on the depth of field from a distance of five feet, we will get the rest of the columns out of focus. all .
It is clear that more distance will give sharpness and more prominence in the second scene. As we focused on a more distant point, here is another important criterion:
The greater the distance you focus on, the greater the depth of field. This is the reason that requires you to rely more on accuracy and care when focusing on close targets than when focusing on distant ones, because the close focus gives a smaller depth of field. Thus, the possibility of error correction is reduced.
Thus, you now know two ways to increase the depth of field:
1- Use a narrower opening.
2- Stay away from the topic more.

**Ali Abbass** · 04-19-2023, 01:27 AM

Depth of field scale:
At a given aperture, you wonder how accurately what will appear in front of the focus point and how accurately what will appear behind the focus point. And the answer is on your camera lens. Perhaps that is because the distance scale on most cameras contains a depth-of-field scale as well. While these scales vary from one camera to another, they are all based on the same basic standard. Take your camera, put the distance scale at ten feet. Chances are that along with the distance scale there is a scale. Another is related to the depth of field and this may contain F numbers. Or it may contain colored code lines or dots indicating /f numbers and for some or all /f stops on the lens.
Find out the depth of field scale in your camera, do you know how this scale works accurately...? If its use is not clear to you, refer to the instruction manual attached to your camera.

Now, let's do a little experiment, put the telemeter in this camera of yours at ten feet. In the table below, write the distances that will be accurately focused according to your depth of field scale. As for the stops shown on your scale, estimate the distance readings as close as possible.

Here, you can clearly see how the depth of field increases as the lens gets narrower. So at F / 4 . You have a depth of just three feet - from 9 feet to 12 feet -. And at F/11, you have a depth of about 9 feet - from about 7 feet to 16 feet -. Whereas at f/16, you have a depth of about 22 feet.
For example, in our table above, we see that the image at F / 4 will appear sharp in protrusion from 9 feet to 12 feet.
Here's another important point: at any pause / f, we get sharply behind the focal point at a distance
An acceptable protrusion, which is longer than the protruding distance with an acceptable sharpness in front of that point, and for example, in our table above, we see that the image at F / 4 will appear sharp in protrusion from 9 feet to 12 feet, and since our focal point is at 10 feet, the image will appear sharp Protruding to a distance of one foot in front and two feet in the back.
At f/8, our depth of field is from 8 feet to 14 feet, meaning that the image will be sharply projected two feet in front of the focal point and four feet behind it. At f/11, our depth of field ranges from about 7 feet to 16 feet, or 3 feet in the front and six feet in the rear - you can use the following as a convenient approximation at moderate distances. At most apertures, one third of the depth of field is in front of the focal point and two thirds are behind it.
is this clear ... ?
Go back to reading the numbers mentioned above if it is not clear to you yet, and you can use this that you have now learned to benefit a lot while planning shots in which the depth of field is important.

Practical notes on depth of field
How precisely do we mean by the sharpness of the protrusion? ...
If a 50mm lens is focused at 10 feet, the depth of field at f/8 is from 8 feet to 14 feet. Does this mean that the prominence of a target 8 or 14 feet away will be the same as the prominence of a target 10 feet away... ?
no . The sharpness of focus is relative and in our ideals, the targets are at a distance of 10 feet prominent with a sharpness of focus that exceeds
The emergence of other targets 8 feet or 14 feet away.
As for now, you have to know the following: In order for it to be within the focus on the point in the subject, it must appear as a point in the negativity, and for each point of precise focus in the negative that is seen under the microscope, it must appear in reality and it is in the form of a minute circle like a cake. It is a circle so small that the naked eye can see it as a point. As for the point that is only slightly out of focus, it will appear as a slightly larger circle under the microscope, and if this slightly larger circle persists in appearing as a point in front of the naked eye, it is in acceptable focus.

The subject of the focal surface becomes larger - and oval, and this is the greater the distance more - until the eye does not see them as points, but rather as blurring. Here, we say about the subject that it is out of focus. All points of the subject that are exactly 10 feet away, will appear on the negative as smaller points, and all points that are further back or less forward by one inch, will appear as slightly larger circles. Then as we move further back or forward, the circles get bigger and bigger.
Hence the distance we call the depth of field. It is that distance in front of and behind the subject, where the points come in the form of small circles to the extent that it is sufficient to see them as mere points with the naked eye. This means in other words that the depth of field is an area with acceptable protrusion sharpness. In our example, the standards of the photography profession view targets from 8 feet to 14 feet as having an acceptable prominence sharpness, while the truth is that targets that are only 10 feet away will be fully in focus.
Know also that what is “acceptably focused” when the print is small may appear out of focus when this print is enlarged and viewed at the same distance. Therefore, the acceptable protrusion sharpness depends partly on the scale of the final print.
Thus, when you use depth of field, it must be used wisely. A subject that is, in acceptable focus, according to the depth-of-field scale, may not be of acceptable prominence for your more demanding eye. As possible, focus on your main topic as accurately as possible.

- A preview of the depth of field:

When you work with SLR cameras with automatic lenses, you see the subject through the viewfinder with the lens wide open, which allows you to watch and focus on the image in its brightest possible glory. Then while pressing the shutter button, the diaphragm automatically narrows until it reaches the aperture you have chosen and the shutter works to expose the film, as soon as the diaphragm returns to widening automatically and until its maximum aperture again. The only problem with this system is that you always view your subject at maximum aperture: which means you're viewing it at the lowest depth of field. So your subject is in sharp focus while everything else is out of focus. Like a tree that seems to be growing from the top of the topic - so what happened...?

What happened is that with an f/2 lens, I saw the scene at f2. However, you shot it at f/16 and what looked out of focus at f/2 was within depth of field at f/16.
To solve this dilemma, many SLR cameras came with a pre-view button (*) for the depth of field. Thus, you can now see the scene as the movie will see it when you press the capture button, look at the background carefully to make sure that there are no obstructive objects in focus. And when you're satisfied with what you're watching, you're ready to shoot.

- orbital focus (*)
when capturing moving subjects. You can work in advance to set the distance scale in your camera and narrow your lens to get the largest possible error correction. This adjustment is known as orbital focus.
Set the distance scale in advance at the distance from which you think you want to shoot. Some examples:
In a party at about eight feet.
In a basketball game, 15 to 20 feet.
At a soccer game, 30 to 50 feet.
Refer to your depth-of-field meter to know the near and far focus limits of the aperture at which you shoot. Whenever your subject enters these limits, you are sure to get an image with reasonable prominence sharpness.

Illustrated examples:

Orbital Focus: When a meter presets a distance of approximately 15 to 20 feet in a basketball game. The photographer who stands at one of the corners of the stadium assures himself that he will get a reasonably focused image, regardless of the speed of the activity.

Ultra focal distance:
Take your camera, and pretend that you are shooting at f/16, then move the distance scale until the infinity sign begins to fall within the f/16 depth-of-field indicators. When you bring infinity and start inserting it into the depth of field, you will have prepared your camera to obtain a reasonable protrusion sharpness for the maximum possible distance on both sides. near and far.
Pictured with an 80mm lens. It appears that the location of this distance at / 16 is 25 feet, and everything from about 12 feet to infinity is of reasonable protrusion sharpness now, although at a different aperture these locations will change for the same lens as they will vary according to the focal length of the lens.
This distance position—the position of the minimum distance that will bring infinity to what is within the depth of field—is called the hyperfocal distance ( * ). It is a very useful way of dealing.
When you don't have time to focus, during a sporting event, for example, you can set up your camera with a small aperture - to give you a maximum depth of field - and then set the distance meter at the super focal distance of that aperture.
Ready to grab, picks quickly tion.

The result is that in this way you have turned your camera into a fixed-focus camera because now you can capture any target that is more than a few feet away - 12 feet in our example - without caring about the issue of focus - as all targets fall automatically within a reasonable focus ⏹

Next lesson
How do professionals use depth of field creatively? !

فن التصوير .. المباديء والمنهاج -٩- التركيز وعمق المجال قوانين ، أنظمة ومقاييس

فن التصوير .. المباديء والمنهاج -٩- التركيز وعمق المجال قوانين ، أنظمة ومقاييس

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