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lens lenghts and fisheyes?

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Hi

I have been thinking this for a while and thought that someone here may be able to explain this to me. I'm confused about lens-lengths and their classification as 'fisheye'. I am well versed with the effect of a fisheye lens and the correction it needs in post, so how can another lens with the same, or less, length, not be a fish-eye. For example Nikons 10.5mm is a fisheye but their 12-24 is not. Perhaps a better example is Canon or Sigma who both have a 15mm fish-eye and a 14mm non fisheye and even a 10-22mm lens that is also non fisheye. With which lens can you see more with? Perhaps lens length is not as closley linked to field of view as I thought.

Any comments greatly appreciated.

 

Thanks

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Hi

 

You should look out a book on photographic optics (Try "the Photographic Lens" by Sidney Ray - focal press, although it is probably out of print by now - page 78 explains!) which will explain the different 'projections' used by lenses to create images.

 

Normal lenses use 'rectilinear' projection, normal fisheyes use 'equidistant' (raely some fisheyes have used 'orthographic'). So the focal length of the lens is not the only determining factor in whether a lens is an ulra-wide or a fisheye.

 

Hope that this helps!

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With which lens can you see more with? Perhaps lens length is not as closley linked to field of view as I thought.

 

Actually, the common idea that shorter focal lengths give wider angle-of-views is correct when comparing "normal lenses" (as Paul explained, they use the same type of projection).

 

When you go to a fisheye lens, the projection type is changed to achieve a very wide angle-of-view (generally 180º or more). So you can't compare a 14mm "normal" lens and 15mm fisheye. You CAN compare the images projected by different fisheye lenses, though. For a good example, check out the images from the 8mm v/s the 15mm Sigma fisheye lenses...

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Following on from this thread, can anyone provide feedback on how fisheye lenses behave with less that full frame cameras? Any recommendations of particular lenses for the Canon platform would also be interesting to hear.

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