PH 103 Dr. Cecilia Vogel Lecture 9

Review Outline  Multiple Lenses  application to microscope  and telescope  Lenses  more corrective lenses  application to magnifier  Angular size and angular magnification

Multiple Lenses  Two lenses -- can do more than cases we discussed for single lens  If you use more than one lens, you can get different results than cases I, II, III.  Just like with mirrors,  You can make an image of an image  with lenses, too.

Multiple Lenses  Making an image of an image with 2 lenses:  The first lens the light goes through  makes the first image.  Then that first image, acts as the “object”  that the second lens will make an image of.  You get a second image, which you see.  If there are more than two lenses,  continue this process  previous lens’ image is next lens’ “object”

Microscope  Two lenses -- can do more magnification than a simple magnifier can  Compound microscope uses 2 lenses.  Type of lenses used in microscope:  two converging lenses  objective lens is near object  eyepiece (or ocular) lens is near eye

Microscope  Objective lens is case I  original object is further than f  but near the focal point  so image is large ( Java applet) Java applet  So first image  produced by objective lens  is real and inverted and larger  m obj = -d i /d o  -d i /f obj

Microscope  Eyepiece lens acts like simple magnifier  M eye = N/d o  N  f eye  Overall magnification  multiply the individual magnifications  M = -(d i /f obj )( N  f eye )  L = tube length Usually |M| is given

Microscope  What should you do to each to make a stronger microscope?  objective -- shorter f obj  tube length -- make it longer, so d i can be bigger.  eyepiece -- shorter f eye final image

Refracting Telescope I  Refracting telescope also uses two converging lenses  One style is like microscope,  except the original object is far away.  The first image is NOT magnified  makes sense, huh? =very far! final image

Image as Real Object  Note that in the telescope at right, the first image  which acts as the object for the second lens  is in front of the second lens  the object for the 2 nd lens is in front of the lens, so it is a real object =very far!

Refracting Telescope I  The image is inverted for this type of telescope  the original object is real,  and the first image is real,  so the magnification due to the first lens is –di/do = -(+)/(+)=(-)  Then the 2 nd object is real,  and the 2 nd image is virtual  so the magnification due to the 2 nd lens is –di/do = -(-)/(+)=(+)  The overall magnification is (-)(+) =(-) =very far!

Refracting Telescope II  Another style of telescope is like microscope, except…  the original object is far away,  and the first image becomes a VIRTUAL object for the second lens =very far!

Image as Virtual Object  What if the first image  which acts as the object for the second lens  is behind the second lens?  the object for the 2 nd lens is behind the lens, so it is a virtual object  & the object distance is negative final image =very far!

Refracting Telescope II  The image is upright for this type of telescope  the original object is real,  and the first image is real,  so the magnification due to the first lens is –di/do = -(+)/(+)=(-)  Then the 2 nd object is VIRTUAL,  and the 2 nd image is virtual  so the magnification due to the 2 nd lens is –di/do = -(-)/(-)=(-)  The overall magnification is (-)(-) =(+) =very far!