Ray Diagrams for Lenses

Convex Lens Ray Diagrams All ray diagrams start with a center line and the lens Note: the lens can be simplified into a straight vertical line

Convex Lens Ray Diagrams On ray diagrams identify and label the following points: P – principle axis C – the optical center F – real focus (focus on side of lens where light rays emerge) F’- virtual focus (focus on side of lens where light rays enter) 2F -Twice the real focal length 2F’- Twice the virtual focal length

Locate and label the focal points (F) Lenses have 2 focal points F (real focal point) and F’ (virtual focal point) The center (C) is located where the lens intersects the center line Draw the object as described in the problem F’ F C

Image Formation http://www.physics.louisville.edu/public/courses/phys111/davis/notes/lo_tl_lens_anim.gif For an image to form multiple rays of light originating from the same point on the object must come together (converge). To locate the image on a ray diagram, a minimum of 2 rays originating from the same point on object must be shown to meet. Typically, we represent the forming of an object with three rays called the principle rays.

Convex Lens – Principal Rays Cutnell & Johnson, Wiley Publishing, Physics 5th Ed. Rays parallel to principal axis are refracted through the real focus (F). 2. Rays through the virtual focus (F’) are refracted parallel to the principal axis. 3. Incident rays along a secondary axis (through O) are not appreciably refracted. Cutnell & Johnson, Wiley Publishing, Physics 5th Ed. Cutnell & Johnson, Wiley Publishing, Physics 5th Ed.

Ray Diagram: do > 2 f draw a ray through near F (virtual) to the lens THEN parallel to the center line (principle axis) (2) draw a ray parallel to the center line to the lens THEN through opposite F (real) (3) draw a ray through C F’ F The point where the refracted rays intersect is where the image will be formed

Ray Diagrams Sketch a ray diagram for the same height of object but moving closer to 2F. Do the same but this time your object is between 2F and F.

Ray Diagram: 2f > do > f draw a ray through near F (virtual) to the lens THEN parallel to the center line (principle axis) (2) draw a ray parallel to the center line to the lens THEN through opposite F (real) (3) draw a ray through C F F

Ray Diagram: do < f draw a ray through near F (virtual) to the lens THEN parallel to the center line (principle axis) (2) draw a ray parallel to the center line to the lens THEN through opposite F (real) (3) draw a ray through C F F If refracted rays do not meet in “real” space, draw dashed lines back from refracted rays so that they intersect behind the lens

What happens when the object is exactly at F? Sketch. http://www.a-levelphysicstutor.com/images/optics/lnss-conv-ray04.jpg No image formed

A convex (converging) lens can form 3 types of images. The type of image is determined by the object distance. do > 2 f IMAGE = real, inverted, smaller F’ F F F’ 2 f > do > f IMAGE = real, inverted, bigger do < f IMAGE = virtual, upright, bigger F’ F

Copywrited by Holt, Rinehart, & Winston Convex Lens

Concave Lens Ray Diagrams All ray diagrams start with a center line and the lens Note: the lens can be simplified into a straight vertical line

Locate and label the focal points: F (real focal point) and F’ (virtual focal point) The center (C) is located where the lens intersects the center line Draw the object as described in the problem F’ F C

Concave Lens – Principal Rays Cutnell & Johnson, Wiley Publishing, Physics 5th Ed. Rays parallel to principal axis are refracted through the virtual focus (F’). 2. Rays through the real focus (F) are refracted parallel to the principal axis. 3. Incident rays along a secondary axis (through O) are not appreciably refracted. Cutnell & Johnson, Wiley Publishing, Physics 5th Ed. Cutnell & Johnson, Wiley Publishing, Physics 5th Ed.

You can only get 1 type of image from a concave (diverging) lens: virtual, upright, smaller draw a ray in line with opposite F to the lens THEN parallel to the center line (2) draw a ray parallel to the center line to the lens THEN in line with near F (3) draw a ray through C F’ F If refracted rays do not meet in “real” space, draw dashed lines back from refracted rays so that they intersect behind the lens

Concave Lens Copywrited by Holt, Rinehart, & Winston