From: noelturntive@live.co.uk   
      
   On Thursday, 2 November 2023 at 16:33:24 UTC, Phil Hobbs wrote:   
   > 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.    
   >    
      
   Thanks for that. It made me think about the possibility of if I had a bigger   
   lens   
   I could watch my tv (upside down and reversed) lying  down on the sofa    
   without my glasses.    
      
   > Cheers    
   >    
   > Phil Hobbs    
   >    
   > --    
   > Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC /    
   > Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics   
      
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