Introduction to Imaging with Lenses Jiefei Wang OPTI 521 December 02, 2008

Overview Introduction Objects & Images Focal Length Imaging Equation Image Movement

Introduction OPTI 521: Opti-Mechanics – Optics determines where to mount optics, and how the elements need to move – Mechanical system holds the optics together to allow it to: Focus on objects at different locations Work over different thermal environments Change field of views Survive vibration/sock

Scope Paraxial Optics – Valid for points “near” the optical axis – Ignores off-axis affects Single Thin-lens – Zero thickness – Refract light perfectly at one plane

Objects & Images The object is the item of interest that the optical system will image Object radiates the light that is collected and imaged by the optics. Image is formed when all the rays of the light are focused by the optics.

Focal Length Object Distance = infinity Image Distance = Focal Length Focal point is the point at which rays from infinity comes to a focus.

Imaging Equation Object Image Focal Point Object Distance Image Distance Focal Length Lens

Object Position vs. Image Position As an object moves towards the lens from infinity the image moves further away from the lens. Image movement is more sensitive to object movement when object is close Focal length is 300mm Object Distance (m) Change in Image Distance (mm) Change in Image Distance vs Object Distance

Object Position vs. ∆Focal Length To keep the image distance fixed, the focal length needs to change. Again the change in focal length is more drastic when the object is close Initial focal length is 300mm

Summary Imaging Equation: Image tends to move more when the object is close to the lens Keeping the image in focus due to object movement becomes harder as the object gets closer to the lens.

Questions?