Focal length comparisons      
         
     
  wide angle lens- canon 17mm on 5D-   fisheye lens-canon 15mm on 5D- 180°angle of view  
         
  shot from the same spot the photograph on the right includes much more area in comparison to the one on the left. However there is much more distortion as well. The walls on the sides are straight and not curved as visible. Also the railing in the foreground is straight and not curved.      
         
         
         
  Same subject shot with different focal lengths keeping the framing and the composition constant- That is, as the focal length was reduced i moved the camera closer to the subject to get almost the same frame. As you glance at the photographs you dont see much of a difference but if you look at them carefully there is quite a difference.      
         
 

Long lens 200mm- since photographed from a distance, the bell and the motiif seem to be close together.

  

70mm- There seems to be more difference between the two elements.

  
         
 

34mm- Tthe difference between the subject, and more so between the bell and the camera is reduced. while shooting with a 200mm lens both the elements were almost at the same distance from the camera but in this case the distance to the bell is less in comparison to the motiff. Also  more of the lower portion is now visible as the camera is closer and hence lower (although it is at the same height as earlier for 200mm shot) Also notice the perspective in the edge of the wall showing up.

  

26mm- More of the lower portion of the bell is visible. The square of the motif also has started showing distortion. the edge of the wall is bending more. there seems to be more gap between the two elements

  
         
         
         
         
         
200mm 130mm 90mm 70mm 50mm
         
     
35mm 24mm 18mm    
Change in perspective with change in focal length.These images were shot using Nikon D200 (not full frame) at different focal lengths starting from 200mm to 18mm. To get the same frame, I walked closer to the chairs while changing the focal length keeping the camera at my eye level. with longer focal length the chairs appear to be closer together and of same size whereas towards the shorter focal lengths the chairs which are closer appear much bigger than those which are away.
   
  200mm Photographed with D200, the cards have been focused in all the three shots. There is minimum distortion in the first shot and maximum in the last one.  
       
  80mm  
       
  18mm(equivalent to 28mm aprox on film format)