Lab 10: Lenses Focal Length Magnification Lens Equation Depth of Field Spherical Aberrations and Curved Focal Plane Chromatic Aberration Astigmatism (Optional) Barrel and Pin Cushion Distortion (Optional) Diverging Lenses Do experiment #5 after all other experiments

Lenses Lab Basic ideas on single lens distances quality of images object, image and focal quality of images photography needs good images on the film problems with single lens

Light Rays ? ? ? ? If there is only one light ray… A light source could be anywhere along the dashed line We sometimes oversimplify ray diagrams by showing only one ray of light and specify the image or source location. This slide challenges students on this concept.

Light Rays Diverging rays give perception of the source location A key concept necessary to identify source location. Diverging rays give perception of the source location

Optical Image Optical elements Diverging light rays This slide extends the concept of source location to concept of image location. Diverging light rays  perception of apparent light source Converging point  image of light source

Light Rays Light rays from far away object appears to be... Some students lack ideas on parallel rays. Where do they originate? How parallel are they? What kind of source generate them?

Parallel Rays Nearly parallel! Huh? We don’t need to pretend that it is parallel. We could also compare with the astronomical distance scale and angles measurable with a protractor. Nearly parallel! Huh?

Converging Lens F F parallel rays converge at F focal length f optical axis parallel rays focal points F F There are too many texts in this slide if shown at once. We need to go through one by one. parallel rays converge at F each lens has a unique f

Ray Diagram tip of arrow parallel real image center through F Image  tip of arrow parallel real image center through F It’s important to point out that this diagram only identifies the location of the tip of the arrow. Image (tip of arrow)

Image Quality  

Image Quality Focused   Sharp image

Image Quality Slightly out of focus   Smeared image

Image Quality Out of focus   No image

Magnification How much larger? 10 or 0.5? Object Image Magnification: ratio of image size to object size

Light Unit Plastic ruler is on the light source! mm Face view mm The manual instructs students to use the plastic ruler to measure the source size. They immediately rush to a meterstick. I always laugh. Ha, ha, ha! Plastic ruler is on the light source! Inner circle diameter: 10 mm