Corso di base - Lezione 13: Lunghezza focale e angolo di campo

Summary

This lesson in photography covers the fundamental concepts of focal length and field of view. The focal length is defined as the distance from the lens to the point of focus on an object at infinity, impacting the magnification and sharpness of the scene. Field of view, in turn, depends on both the focal length and the size of the sensor. The script also explores how sensor size affects the angle of view, with smaller sensors capturing narrower fields and larger sensors capturing wider ones. The video ties these ideas to depth of field, highlighting how sensor size and focal length shape both the composition and focus in photography.

Takeaways

• 😀 Focal length is the distance from the lens to the point where an image is focused, typically at infinity for distant objects.
• 😀 The focal length of a lens determines how much of a scene is captured in the frame. A longer focal length captures a narrower view, while a shorter one captures a wider view.
• 😀 The field of view is influenced by both the focal length and the size of the sensor. A larger sensor captures a wider field of view.
• 😀 A lens with a short focal length, such as 50mm, can produce a wide-angle effect on a smaller sensor, but behave like a telephoto lens on a larger sensor.
• 😀 Sensor size plays a critical role in how focal length affects field of view. A smaller sensor has a narrower angle of view with the same lens.
• 😀 Depth of field is closely linked to focal length. Longer focal lengths result in a shallower depth of field, whereas shorter ones produce a deeper depth of field.
• 😀 Smaller sensors require lenses with shorter focal lengths to achieve equivalent compositions compared to larger sensors.
• 😀 Using a short focal length on a small sensor results in a large depth of field, allowing for clear focus on both near and distant objects.
• 😀 Larger sensors (e.g., full-frame) require longer lenses to capture the same field of view as smaller sensors, which affects the perspective and depth of field.
• 😀 The connection between focal length, field of view, and sensor size means that a lens can be classified as wide-angle or telephoto depending on the sensor size it is paired with.

Q & A

What is focal length in photography?

Focal length is the distance from the center of the lens to the image plane (such as the film or sensor) where an object at infinity is focused. It determines the magnification of the scene and affects the field of view.

How does the sensor size affect the field of view?

The field of view is influenced not just by the focal length of the lens but also by the size of the sensor. A larger sensor captures a wider field of view for the same focal length, while a smaller sensor results in a narrower field of view.

What is the relationship between focal length and depth of field?

Focal length influences the depth of field. Longer focal lengths create a shallower depth of field, while shorter focal lengths increase the depth of field, making more of the scene appear in focus.

How does the size of the sensor impact depth of field?

Smaller sensors generally have a greater depth of field, meaning more of the scene is in focus. Larger sensors, on the other hand, tend to have a shallower depth of field, which is desirable for artistic effects like background blur.

Can the same lens behave differently depending on the sensor size?

Yes, the same lens can behave differently depending on the sensor size. For example, a wide-angle lens on a small sensor can function like a telephoto lens on a larger sensor, altering the field of view.

What happens when you use a very small sensor like in compact cameras?

Compact cameras with small sensors often require very short focal lengths, allowing them to have a large depth of field, keeping both near and distant objects in focus simultaneously.

What is the effect of using a long focal length on a larger sensor?

Using a long focal length on a larger sensor results in a narrow field of view and a shallower depth of field. This combination allows for detailed, magnified images of distant subjects.

What is the difference between a wide-angle lens and a telephoto lens?

A wide-angle lens captures a large field of view, ideal for landscapes and architectural shots, while a telephoto lens captures a narrow field of view, ideal for magnifying distant subjects.

How does focal length relate to the 'angle of view' or field of view?

The focal length determines the angle of view. A shorter focal length (wide-angle lens) provides a larger angle of view, while a longer focal length (telephoto lens) provides a smaller angle of view.

Why does the same focal length produce different results on different sensors?

The same focal length produces different results on different sensors due to the sensor size. A smaller sensor crops the image, resulting in a narrower field of view, while a larger sensor captures more of the scene, offering a wider field of view.