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Camera, Lens, Parallax...

Updated: Dec 2, 2022

In this article, we will try to explain the main features of the camera and especially the lenses, and the lens selections according to the conditions by explaining the commonly used terms.

A modern camera is a digital image recorder working via the lens focusing scattered rays to the sensor and in the sensor a filter called Bayer seperates colors and sends photons to photosites in sensor then those photons are converted to digital data.

Video cameras are devices that can record images at certain frequencies. The minimum frequency required for the human eye to perceive an image as moving is 24 frames per second (fps, frame per second = Hertz). This has also been adopted as the motion picture standard. Apart from this, different fps values are used in various parts of the world in the TV industry. While the NTSC standard used in the Americas and Far East regions uses 29.97 fps / hz, the PAL 25 fps / hz standard is used in many countries as standard, especially in Europe.

There is a common misconception that the human eye can detect a maximum of 25,30,60 hertz/fps. This situation has emerged as a result of the deterioration of the minimum number of frames required to perceive the image as moving, which we mentioned above. Therefore, there is no such thing as the maximum fps/hz that the human eye can detect. Various monitor manufacturers produce monitors with a refresh rate of over 200hz for gamers.

Today, camcorders that fit in a shirt pocket can record images up to 1000 fps. When 1000 frames in one second are read at 25 frames per second, it allows the movements of fast objects (bullet, etc.) that could possibly escape our perception, to be seen by slowing down. This is known as slow motion, super slow motion and ultra slow motion. More advanced cameras can reach values such as 100,000 fps.


The lens is an essential part of the camera. If we say that if there is no lens, there is no camera, we would not be wrong. When we operate the camera without a lens, scattered beams of light coming from every possible angle falling on the sensor will give us a useless image with maximum blur.

When we use lens, the convex glass pieces in the mechanism collects the scattered light through a process called converge, and the collected light passes through different glass pieces and falls on the sensor properly focused. This allows us to obtain a clear image. Conversely, concave glass pieces scatters focused light beams with the diverge process, which is the opposite of converge. Why should we use a concave glass to diffuse the light when our purpose is to focus the light?

When you put a concave glass that can move back and forth between two convex glasses, we gain the magnification feature of the image called zoom. This is the basic of zoom lenses.

By examining the picture, you can see the magnification effect according to the position of the concave glass:

Focal Length

Focal Length is the measure specified as 18mm 24mm 70mm etc. which we see on lenses. What it is, how it works? Those mm values has nothing to do with lens glass piece sizes.

It simply indicates the distance between the converge point of the light and the sensor. Examine the picture:

The effect of Focal Length is briefly as follows: As the value increases, the magnification increases and the angle of view decreases. As the value decreases, the angle of view increases and the magnification decreases.

At this point, we need to open a perspective-parallax bracket to connect to the industry.

Size of an object has two different definition. Real size and visible size.

  • Real size is just real size width, length, meter, inches etc..

  • Visible size, on the other hand, changes in proportion to the proximity and distance of the object to the viewer, and its size measured in degrees.

Simple, the object appears larger as it approaches and smaller as it moves away. This is what we call Perspective Distortion (Below...). The main thing is the parallax effect caused by the camera's Focal Length, movement and distance between objects.

Let's examine the diagram showing the FL, Visible Angle, Wide, Telephoto relationship:

You can inspect the image by right click open big size.

When we use a wide-angle lens, two main factors come to the fore:

1 - High ratio in visible size between the near object and the far object.

2 - When we move the camera, the far object moves slower than the near object.

Both squares are the same size. The green square is 500 units behind the red square.

At Wide angle (15 mm) the visible size and movement speed of green is low, while at Telephoto (80 mm) the sizes and speed are almost equal. Notice that we had to pull back Tele cam in order to equalize the size of red squares due to magnification effect of Tele.

At this point, let's talk about which setup requires what settings. Focal Length-based different visual styles have emerged in the advertising and television field of the sector. We can list some of the main styles as 3D, Flat and Isometric.

3d - 3d works usually consist of scene setups with depth. Objects have depth of their own and there is depth between objects. The Environment is full. In the scene we designed, we need to use a Focal Length from the Wide Angle family (35mm and below) in order to fit the more object and scene into the frame, to make the depth and 3D perceivable in the camera movements, and to bring the objects in focus. In wide angle we perceive parallax effect clearly.

Flat - In such works, the self depth of the object and the depth between the objects are low. The visible size of the objects and the actual size are more proportional and closer to the true. When we prepare a 3D scene, to make it flat, we can use Telephoto lenses. In this style, objects in focus can be distinguished from other objects by light, color, contrast, and shallow depth of field (discussed below).

Notice lack of depth and color contrast.

Isometric - High Focal Length is used in this style. (Telephoto, Super Telephoto, < 130 mm) Such a high mm makes the front surface and back surface of a cube look the same size. It removes the near-far object perception and shows all objects proportional to their own real dimensions. It reduces the parallax effect caused by the movement of the camera to almost zero. All in all, it removes perspective:

Note that all cubes near and far have the same size and movement speed.

While we are here let's examine the effect of Distortion. Each lens produces varying degrees of distortion. Some are obvious, while others may be so low that they are almost imperceptible.

There is two types of distortion. Optical and Perspective.

Optical Distortion

OD is a type of error caused by the design of the lens. In order to prevent this in modern and advanced lenses, many elements are added to the lens. But such lenses are rare and expensive.

In short, OD is the straight lines appearing bended due to lens shape. There is also two types of Optical Distortion: Barrel Distortion and Pinchusion Distortion.

Barrel Distortion (Convex) - BD results from the angle of view being much larger than the sensor. Inward squeeze is required to fit the image on the sensor. This means that the linearity is deteriorated convexly, especially towards the corners since the center is reference point the edges always gets distorted. It is the effect seen with most wide-angle and even standard lenses.

Pinchusion Distortion (Concave) - PD is the opposite of BD.. The angle of view is very low compared to the sensor and the image needs to be stretched to fit the sensor. This again means a concave deterioration of the linearity, especially towards the corners. It is an effect seen in telephoto lenses.

Perspective Distortion (PD)

PD is a natural type of distortion not related to the lens. Close objects appear larger due to the perspective effect. This is both true for the object-background relation and object's self depth.

Let's take the handsome brother in the picture. The leftmost wide-angle lens (24mm) visually enlarged the parts of the brother close to the lens (note the nose) while making the rest smaller (nearly absent of the ears).

In the rightmost 50 mm ideal lens, the brother's face appears in an ideal shape and average, which is a Focal Length close to the vision of the human eye.

Now, the important point here is that in order to camera covers same size of the face in framing we need to pull the camera back while Focal Length increases. Pulling back the camera means changing the perspective. In other words, standard or telephoto lenses do not prevent perspective distortion, they move the object or camera away due to their magnification effects. This is a change of perspective. This is how the human eye works.

Let's take the wide-angle picture on the far left. If we move the camera to the position of the far right camera, bro will appear quite small in the image compared to the one on the right.

En soldaki geniş açı resmi ele alalım. Eğer kamerayı en sağdaki kameranın pozisyonuna getirirsek, abi, görüntüde sağdakine göre epey küçük görünecektir. But if we crop the image to equalize the size, we can see that the Perspective distortion rate is exactly the same.

You can see the view angle, distance, PD relationship in the following gif:


The aperture is a hole-shaped curtain that regulates the amount of light that enters through the lens.

Measures with f.

As can be seen in the picture, as the f value decreases as the number, the curtain opens, the amount of light entering increases, and as the f value increases as the number, the opposite effect occurs.

Since the mathematical properties of circular structures such as radius, π (pi) are used in the calculation of the values here, there is no linear trend such as 2,4,8,16. Each value you see above receives twice or half as much light as the next one.

The only thing to remember is High f value = low number = more light. Low f value = high number = less light.

Changing the f value also controls some different effects apart from the amount of light entering:

  • High f value ( f/1.4! ) causes high optical distortion (aberration, distortion). Distortion can be corrected by lowering the f value.

  • High f value causes the shadow of the diaphragm to fall on the sensor, which we call vignette. Vignetting can be reduced by lowering the f value.

  • Hight f value means a lot of rays from very different angles reaching to lens and sensor which means less focused rays and relatively blurry image. Important point is figuring out the sweet spot of f value. If we decrease f value too much this will cause less rays reaching to sensor and leads to the same image with sharpness issue.

  • High f value means shallow depth of field. We can increase depth of field by lowering f value.

Depth of Field (DOF)

To put it simply, DOF is the range between the closest and furthest distance that can be focused depending on lens specifications.

After a certain distance (hyperfocal), focusing to infinite distance, called Infinity Focus, which is found in many lenses, comes into play.

If focus is set to infinity, everything looks slightly blurry. Therefore, in order to focus distant objects such as stars, moon, etc., fine adjustment is required around infinity.

Due to the nature of each lens, there is a minimum focusing distance. If the minimum focusing distance of a lens is 10 cm, the object 10 cm away from the lens will appear in focus, if you get any closer than that, the object will begin to blur. Do not expect to get a clear image by putting your finger on the lens.

Min, max and set focus distances are indicated on the lens.

Focus point is the distance at which full focus is. It can be adjusted to a point between the min and max distances with the focus ring. Objects that are in front or behind of the focus point are blurred according to their distance.

DOF can be set as Shallow-Narrow or Deep-Large with Aperture.

Just we mentioned above, if we increase f-stop (decreasing value!) we can get a narrow depth while with decreasing (increasing the value!) we get large depth.

When we set the lens to infinite focus we can think of it is an extra large depth of field which a lot of time it is used to show everything as crisp as possible mostly for the environment shots.

However... Depth of Field will still be under the effect of blurring. When we shot an environment we can decrease f-stop to get an image frame as crisp as possible. Yet when we inspect the shot we still be able to see different levels of blurriness and crispness between close and distant. In order to get maximum overall crispness we should consider the area or objects in range of Depth of Field, pushing things inside this range to out of frame, at least the closest ones. If we include ground near us in frame, it will be blurred no matter how slightly you adjust your focus in infinite plane or decrease f-sfop.

Lets finish it here for now.

Stay safe!

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