OpticsRealm Tutorial - 12 - Stops and pupils

Summary

This tutorial from the YouTube channel 'optics' dives into the concept of aperture stops and pupils in optical systems. It explains the role of the aperture stop in limiting on-axis and off-axis rays, discusses the significance of pupils in imaging systems, and clarifies misconceptions about entrance and exit pupils. The video also covers how to locate pupils and the importance of pupil magnification in photography. It concludes with the concept of telecentric lenses and their impact on optical performance, providing a comprehensive guide for those interested in the fundamentals of optics.

Takeaways

• 🔍 The aperture stop is the single aperture in an optical system that limits the on-axis beam and also affects the off-axis rays to prevent vignetting.
• 🌀 Pupil aberrations can skew the rays and are an advanced topic in optical imaging aberrations.
• 👀 The entrance pupil is not necessarily at the front of the lens; it is located where the chief ray crosses the optical axis.
• 📏 To find the entrance pupil's size, trace the marginal rays backward to the point where they intersect with the optical axis.
• 🔬 The double Gauss lens system, common in camera lenses, has an aperture stop that is not near an optical surface and can be adjusted with an iris.
• 📦 Viewing an optical system as a 'black box' allows for the simulation of light bundles' movement by knowing the location of the entrance pupil.
• 👁 The exit pupil is the view of the aperture stop as seen from the image space and is important for understanding relative illumination.
• 🔄 Pupil magnification, or pupil ratio, is the diameter of the exit pupil divided by the diameter of the entrance pupil, useful in close-up photography.
• 🌟 Telecentric lenses are designed to place the exit pupil at infinity, which can affect the balance of spherical aberration and imaging quality.
• 🎓 Understanding pupils is crucial for aligning the eye's pupil with the exit pupil in devices like microscopes and rifle scopes for optimal viewing.
• 📝 The script provides a comprehensive tutorial on aperture stops, pupils, and their roles in an imaging system, with practical examples and definitions.

Q & A

What is the aperture stop in an optical system?

The aperture stop is the single aperture in the optical system that limits the on-axis beam of light. It can be a piece of metal with a hole, an iris, an optical surface, or a lens. It also limits the ray bundle for off-axis beams to prevent vignetting.

How does the aperture stop affect the imaging system?

The aperture stop determines the size of the beam of light that enters the optical system, which in turn affects the quality and characteristics of the image formed. It is crucial for controlling the amount of light and the depth of field in the image.

What are pupil aberrations and how do they relate to the aperture stop?

Pupil aberrations are optical imperfections that distort the path of light rays as they pass through the aperture stop. These aberrations can skew the rays, affecting the clarity and quality of the image.

How is the entrance pupil defined in an optical system?

The entrance pupil is the image of the aperture stop as seen from the object space. It is located wherever the chief ray, traced from the object, crosses the optical axis.

What is the significance of tracing the chief ray to find the entrance pupil?

Tracing the chief ray helps determine the location of the entrance pupil, which is crucial for understanding how light enters the optical system and how it is manipulated by the system to form an image.

How does the double Gauss lens system handle the aperture stop?

In a double Gauss lens system, the aperture stop is typically buried within the optical system, not near an optical surface. This allows for the use of an iris to vary the F number, which adjusts the amount of light entering the system.

What is the difference between the entrance pupil and the exit pupil?

The entrance pupil is the image of the aperture stop in the object space, while the exit pupil is the image of the aperture stop as seen from the image space. The entrance pupil determines how light enters the system, and the exit pupil determines how it exits.

Why is the location of the exit pupil important for relative illumination calculations?

The exit pupil's location is crucial for calculating the uniformity of illumination across the image plane. It helps determine how light is distributed, which can affect the brightness and contrast in different parts of the image.

What is pupil magnification and how is it calculated?

Pupil magnification is the ratio of the diameter of the exit pupil to the diameter of the entrance pupil. It is used in photography for close-up imaging and helps understand how the size of the pupils changes as light passes through the optical system.

What does it mean to telecentric a lens and why is it important?

Telecentricing a lens involves adding a lens to collimate the chief rays or to place the exit pupil at infinity. This ensures that the chief rays are parallel, which is important for applications like microscopy where uniform illumination and precise focusing are critical.