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12-13-2006, 07:04 AM   #1
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which focal length(s) are considered "fish eye"?

I was just wondering exactly what focal lengths designate a lens a fish eye. some lenses are not called fish eye but are the same focal length(s) that other lenses, which are called fish eye.
I know what fish eye means, I am just confused about the above issue.

thanks ahead of time!


12-13-2006, 07:52 AM   #2
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Fisheye lenses do not have a set focal length, but they usually have a FOV of around 180 degrees diagonally All a lens has to do to become a fisheye is distort the image in a circular pattern- it adds more FOV in exchange for a distorted view (which is often a cool effect).

So, ultra-wide angle lenses like the 12-24mm DA or the 15mm K aren't fisheyes; they're known as "rectilinear" since they don't distort the image.

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12-13-2006, 08:34 AM   #3
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As Mo already pointed out it's the projection method that makes the difference between a fish eye and a "normal" lens; a "corrected" lens with rectilinear projection shows straight lines straight - a fish eye lens opts for a projection that bends lines that are not in the center, but can encompass a larger FOV in exchange (up to 220 degrees ... at least that was the fish eye actually built with the largest FOV I know of). AFAIK most fish eye lenses use equisolid angle projection (don't ask me what it is - but it does curve the lines at the borders!!).

So not the focal length is important for determining if a lens is a fish eye or not, but only the projection method used. For example the 16mm Zenitar does not offer a 180 degree view from corner to corner if used on a digital APS-C body, but still is a fish eye. The DA12-24 is not a fish eye at 12mm focal length, but the DA10-17 is at the same focal length.

Rule of thumb is also that at a given focal length the FOV offered by a fish eye lens is greater compared to a rectilinear lens with the same focal length. That's why a de-fished Zenitar offers a wider view compared to a DA16-45 at its widest angle.

12-13-2006, 10:51 AM   #4
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Thank you Mo and phil!

much appreciated.... well understood now



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