From: pcdhSpamMeSenseless@electrooptical.net   
      
   Lou  wrote:   
   > I am short sighted so anything at arms length or beyond is *completely* out   
   of focus.   
   > Just noticed though that if I hold a pair of reading glasses ( not mine   
   > as I don’t need them for close up vision) at arms length the frame and   
   > everything around is out of focus as usual but the image coming through   
   > the lens of the background  scene is in complete 20:20 sharp focus .Albeit   
   upside down.   
   > Cant quite figure out how this works. Is it something to do with the   
   > focal length in my eye between the lens and retina?   
   >   
      
   You‘ve invented the telescope. ;)   
      
   The reading glasses are forming a real image (aka an aerial image) between   
   them and your eyes.  Because the glasses’ focal length is short, the image   
   is far enough away that you can focus on it.   
      
   If you draw a ray diagram, you will see why the image is rotated 180   
   degrees—inverting in both x and y directions is equivalent to a half turn.   
      
   Cheers   
      
   Phil Hobbs   
      
   --   
   Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /   
   Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)