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Lenses in perspective

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The tree images are taken with the same camera from the same camera position using three different focal lengths, 12, 35 and 75 mm. The top line shows the images cropped to the show the central part and the lower row shows the full image.

 

What the images show is that the perspective, that is the proportion between the size of the subjects, does not change. (A deeper discussion of perspective is given here) On the other hand, using a different focal length allows us to choose another perspective. The lower row of images also illustrates that field of view is very different, giving a very different visual impact for each lens, although the perspective is technically speaking identical.

 

12mm cropped 35mm cropped 75 mm cropped
12mm ucropped 35mm uncropped 75 mm uncropped

Changing perspective by moving point of view

A different lens will allow us to change point of view. The image below shows the fountain about the same size as the previous shots. The image was taken with a 15 mm lesn, allowing the camera to stand much closer to the fountain and thus changing proportions.

Projection

Another issue related to perspective is projection. There are different projections:
  • Rectilinear projection is what is normally used. Parallell lines are kept striaght but may converge.
  • Cylindrical projection is often used for panoramas. In cylindrical perpective horizontal lines are curved and converge while vertical lines are parallell and straight
  • Spherical projection is used by "fisheye" lenses
Rectilinear projection is not possible for very wide angular field. In practice rectilinear projection is limited to around 115° angular field (horizontally).
The images below are made from three stitched images. The same images were used but the projection is different.
Rectilinear Cylindrical

Fisheye

Another projection is used by "fisheye" lenses. In this projection only lines passing trough the center are straight but all other lines are curved.

 

Last Updated on Wednesday, 15 February 2012 15:02  

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