DyM Podcast

In This Episode, I talk about the fundemental principle of optics and imaging geomerties.

Choosing the right focal length for a lens based on the desired field of view (FOV) involves understanding the relationship between focal length, sensor size, and FOV. Here’s how you can approach it:

1. Understand the Basics:

• Focal Length: This is the distance between the lens and the camera’s sensor when the subject is in focus. It is measured in millimeters (mm). A shorter focal length gives a wider FOV, while a longer focal length gives a narrower FOV.
• Field of View (FOV): This refers to the extent of the observable world that is seen at any given moment through the lens. It’s typically measured in degrees.
• Sensor Size: The size of the camera sensor (e.g., full-frame, APS-C, micro four-thirds) also affects the FOV. A smaller sensor will crop the image, leading to a narrower FOV.

2. Calculate Field of View:

• Full-Frame Sensor (35mm equivalent):
  • A 50mm lens on a full-frame camera is considered “normal,” as it closely approximates the human eye’s field of view.
  • Wide-angle lenses (e.g., 24mm) provide a wider FOV.
  • Telephoto lenses (e.g., 85mm, 200mm) provide a narrower FOV.
• Crop Sensors (APS-C, Micro Four Thirds):
  • The effective focal length is multiplied by the crop factor (1.5x for APS-C, 2x for Micro Four Third

The mathematical relationship between the focal length of a lens, the working distance (distance from the lens to the subject), and the sensor size is essential in understanding how to control the field of view. The formulas you need are related to basic optics principles, and you can derive these relationships through the following equations:

1. Magnification Equation:

2. Lens Equation (Thin Lens Formula):

3. Field of View (FOV) Formula:

4. Working Distance Calculation:

5. Approximation for Distant Subjects:

6. Practical Example:

I hope you enjoyed this Episode, please let me know your thoughts in the comment section.