Midterm Exam. Lasers. Gases and pressure. Lenses so far. Lenses and Cameras 4/9/2017. Office hours

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1 Lights. Action. Phys 00, Day : Cameras Reminders: HW 9 due NOW and 0pm tonight on DL Lab 8 today/tomorrow AB and EH by THURSDAY i you need to do a make up lab MT 3 on THURSDAY Exam Thursday in class Midterm Exam Same ormat and rules as last midterm Bring up to 7 handwritten note cards. Bring a SCIENTIFIC, NON-GRAPHICAL calculator Bring pencil, eraser, RULER, student ID. Oice hours EXTRA review sessions: 3-4pm Tues, -pm Wed in LAB area. - LA review sheets will be available - Also use the lens lab to solidiy your knowledge o lenses ask questions! I will be available ~ am in the physics lounge on Thursday and over No oice hours on 4/4 or -3pm on 4/7 AB WILL be available on 4/7 -pm, helproom Gases and pressure Fluids exert pressure on suraces when randomly moving particles collide with and bounce o suraces Ideal gas law: PV = knt Atmospheric pressure equal to weight o atmosphere ABOVE per unit area Buoyancy orce: Particles o luid bump into and exert orce on all sides o object Forces on sides cancel out Pressure at bottom greater than pressure at top (more luid above), and so upwards orce on bottom greater than downwards orce on top Net orce in upwards direction, the buoyancy orce Archimedes: Buoyancy orce equal to weight o luid displaced Will it sink or loat: Compare densities o luid and object. (balance between weight and buoyancy orce) Lasers What makes laser light special? How does a laser work? a) Requirements: - Stimulated emission - Population inversion - Optical eedback b) Dierent lasers - Gas discharge laser (He-Ne, CO ) - Diode laser (laser pointer) 3 Lenses and Cameras How lenses work - Focal length Forming an image - Where? - How big? Depth o ield Camera settings - Aperture (/#) - Shutter speed - Exposure Lenses so ar Lenses use reraction to bend light Light rom each point on object reocused to a point on the image Parallel light ocused to a point one ocal length ( ) ater lens. Focal length () Converging and diverging lenses Ray tracing to ind position and size o image Trace 3 special rays rom point on object (not on axis) through the lens Image o that point orms where they intersect

Finding the image Ray tracing to ind position and size o image - Trace 3 special rays rom point on object (not on axis) through the lens - Image o that point orms where they intersect Why is the iris

Thin lens equation: = o + i Size o image proportional to i : : h i h o = i o What will happen at screen i close down iris in ront o lens? a. Images brighter and object more in ocus b.

Images dimmer and object more out o ocus 7 8 Depth o ield F-number (/#) controls image brightness F-number (/#) = / d d Small aperture Large depth o ield Daodils and background in ocus Increase

2 Finding the image Ray tracing to ind position and size o image - Trace 3 special rays rom point on object (not on axis) through the lens - Image o that point orms where they intersect Why is the iris (aperture) important? Consider objects at dierent distances rom lens Iris h o o i Axis o lens h i Screen at Focus o. Thin lens equation: = o + i Size o image proportional to i : : h i h o = i o What will happen at screen i close down iris in ront o lens? a. Images brighter and object more in ocus b. Images dimmer and object more in ocus c. Images brighter and object more out o ocus d. Images dimmer and object more out o ocus 7 8 Depth o ield F-number (/#) controls image brightness F-number (/#) = / d d Small aperture Large depth o ield Daodils and background in ocus Increase aperture diameter by 6 Small depth o ield Daodils in ocus Background is blurred /# Large: Focal length large (light spread over larger area) Small diameter lens (less light captured) Dimmer image. /# Small: Focal length small (light spread over smaller area) Larger diameter lens (more light captured) Brighter image. 0 Application: Setting up a manual camera OR. so that s what the numbers on my camera mean! OR...thank goodness or automatic cameras!. Setting the aperture Standard -numbers (/d) (or -stops) For a given lens, /# setting controls aperture diameter Series o standard /# settings called -stops F-stops increase by actor o (~.4) Increasing F-stop by decreases aperture area by. (Aperture diamater ) Aperture setting (/# or stops) Shutter speed Exposure How to pick the right combination o the above /, /.8, /4, /5.6, /8, /, /6, / Smaller /# Larger aperture Brighter image Smaller DOF Standard -stops Larger /# Smaller aperture Dimmer image Larger DOF 35mm lens set to /

Correctly exposed Over-exposed Fast e.g.

3 . Setting the shutter speed Length o time shutter is open in seconds Standard shutter speeds increase by a actor o./000, /000, /500, /50, /5, /60, /30,,,,,,s 3. Exposure - The amount o light per area reaching the ilm For a given lens: Exposure aperture area exposure time (shutter speed) /(/#) exposure time Pinwheel at dierent shutter speeds Under-exposed Correctly exposed Over-exposed Fast e.g. /4000s Medium e.g. /5s Slower e.g. /30 s Shutter speed knob Choose exposure settings based on: - Scene lighting - Film speed (light sensitivity o ilm) - Desired appearance o photograph Aperture and shutter speed combinations Exposure /(/#) exposure time You can get the same exposure using a range o dierent aperture and shutter speed settings Example: I get the correct exposure i I use an aperture o / and a shutter speed o /5 s To achieve approximately the same exposure what shutter speed do I need i I use an aperture o /5.6? a) /5 s b) /50 s c) /500s d) /60s e) /30s Aperture and shutter speed combinations I determine the required exposure (with a lightmeter). How do I pick the aperture and shutter speed combination? Consider: - Motion o subject - Motion o camera - do I have a tripod? Prioritize - Depth o ield Example: I photograph 00m sprinters at a track and ield event. I want to ensure that my pictures are not blurred What would the most suitable shutter speed be? a) /000s b) /5s c) /4s With such a ast shutter speed (/000s) I need to use a large aperture to get enough light on the ilm and get the exposure correct. I m shooting rom the side o the track With these settings, is it likely that I ll get all the athletes in ocus? a) Yes A large aperture will have a large depth o ield b) No A large aperture will have a small depth o ield c) Yes the ast shutter speed will prevent blurring o the entire image d) Depends on the ilm speed Photography summary When setting up a photograph I need to consider A) Exposure - How much light is there (measure with lightmeter) - What ilm speed do I have B) Aperture and shutter speed. Together they achieve the desired exposure Prioritize the ollowing: - Motion o subject or camera - Depth o ield - Special eects For the rest o us. Thank goodness or automatic cameras! 3

Vision correction How does the eye orm an image? What does 0/0 vision mean?

Weaker lens o variable ocal length - Enables us to ocus on objects at dierent distances Furthest distance that the test subject can see object Examples: 0/30 Furthest distance that a person with

- Can see at 0 eet what someone with normal vision can see at 40 eet - Can only see letters that are twice as large as someone with normal vision 0/5 vision - Better than normal http://www.bgsm.

4 Vision correction How does the eye orm an image? What does 0/0 vision mean? Visual acuity is usually measured with a Snellen chart Snellen chart T he eye uses lenses to orm a sharp image on the retina : Cornea Strong lens o ixed ocal length does most o the ocusing Eyelens Weaker lens o variable ocal length - Enables us to ocus on objects at dierent distances Furthest distance that the test subject can see object Examples: 0/30 Furthest distance that a person with normal vision can see object cornea eyelens retina 0/0 vision - Normal 0/40 vision - Worse than normal. - Can see at 0 eet what someone with normal vision can see at 40 eet - Can only see letters that are twice as large as someone with normal vision 0/5 vision - Better than normal Levels o Vision * 0/0 - Normal vision. Fighter pilot minimum. Required to read the stock quotes in the newspaper, or numbers in the telephone book. * 0/40 - Able to pass Driver's License Test in all 50 States. Most printed material is at this level. Common Eye problems - Near and ar-sightedness Relaxed eyes viewing a distant object retina * 0/80 - Able to read alarm clock at 0 eet. News Headlines are this size. * 0/00 - Legal blindness. Able to see STOP sign letters. * For normal vision, the ar point (or arthest point that can be seen) is usually ininity. * For normal vision, the near point (or closest point that can be seen) is 5 cm. Normal Myopic (Near-sighted) Hyperopic (Far-sighted) Primarily determined by: Shape o cornea (crude ocusing) Length o eyeball Myopia short sightedness What the world looks like Treatments or myopia Glasses Contact lenses Eye surgery latten the cornea, increase ocal length Radial keratotomy Photoreractive keratotomy (PRK) LASIK Facts in 4 Americans Starts in early teens as eyeball lengthens Cause probably genetic Not caused by TV, reading too young, etc Foreground clear Distant objects blurred 4

Radial Keratotomy Photoreractive keratotomy (PRK) Uses a computer controlled eximer laser Laser emits pulses lasting only billionths o a second Laser vaporises microscopic slivers

Procedure takes - minutes Procedure is pain ree but 0-0% o people eel pain or weeks aterwards 95% achieve 0/40 vision or better LASIK Cut several spoke-like slits in the cornea

85% o people achieve 0/40 vision or better Like PRK but perormed deeper inside the cornea A surace lap is removed and then replaced to give access inside cornea.

5 Radial Keratotomy Photoreractive keratotomy (PRK) Uses a computer controlled eximer laser Laser emits pulses lasting only billionths o a second Laser vaporises microscopic slivers rom the cornea theoretically making very accurate and speciic modiications to its shape. Procedure takes - minutes Procedure is pain ree but 0-0% o people eel pain or weeks aterwards 95% achieve 0/40 vision or better LASIK Cut several spoke-like slits in the cornea with a diamond knie Causes central area to latten and ocal length increase. 85% o people achieve 0/40 vision or better Like PRK but perormed deeper inside the cornea A surace lap is removed and then replaced to give access inside cornea. Generally results in quicker and less painul recovery than PRK Early studies suggest better inal vision than RK or PRK Question on myopia Question on hyperopia To correct or myopia or near-sightedness, your glasses need to contain: A. Positive (converging) lenses B. Negative (diverging) lenses C. Biocals To correct or hyperopia, do you need glasses with: A: Convex lens B: Concave lens C: Biocals 5

Lights. Action. Cameras. Shutter/Iris Lens With focal length f. Image Distance. Object. Distance

Lights. Action. Cameras. Shutter/Iris Lens With focal length f. Image Distance. Object. Distance Lights. Action. Phys 1020, Day 17: Cameras, Blm 15.1 Reminders: HW 8 in/hw 9 out Make up lab week straight ater Sp.B. Check scores on CU learn 1 Object Cameras Shutter/Iris Lens With ocal length Dark Box