Fisheye Lenses
Why do we call a Fisheye a Fisheye?
The name Fisheye was coined by R.W. Wood to refer to any
lens capable of imaging the entire hemisphere in object space onto a finite
circle in the focal plane. He chose Fisheye name because a fish looking
upward at the surface of the water will see the whole sky imaged as a finite
circle this way.
There are two types of Fisheye lenses:
- The first type of Fisheye lens has a 180 degree field of view
in all directions and results in a circular image on 35mm film. These Fisheye
lenses typically have a focal length around 8mm. Among this type of Fisheye
lenses Peleng 8mm f3.5 Fisheye lens is. You may order this Fisheye
lens from RuGift.com
- The second type of Fisheye is known as a "full frame Fisheye"
and they cover the entire 35mm frame, with a 180 degree diagonal field of
view. Typical horizontal coverage of this type of Fisheye lens is
around 140 degrees, typical vertical coverage is around 90 degrees, focal
length is 15 or 16mm. Among this type of Fisheye lenses Zenitar 16mm
f2.8 Fisheye lens and Zodiak 8 (Arsat) Fisheye 3,5/30 Lens is. You may order
these Fisheye lenses from RuGift.com
The Fisheye lens - in one exception in the family of wide
angle lenses.
Fisheye lens is not so commonly used; the prize is often
higher compared to other wide angle lenses and it is generally considered as
having very limited use. Already the name however, should make the diving photographer
alert: Fisheye !!!
Fisheye type of lens produces extraordinary results at underwater photography.
How come? Here are some properties of Fisheye lens type:
- The Fisheye lens has an angle of view of 180 degrees. There are
two types of Fisheye lenses. The subject here is the so called "full
frame Fisheye" lens, having this angle of view along the diagonal
of the picture and thus "filling the full frame". We also have the second
kind of Fisheye lens, which is giving a round picture of 180 degrees, utilizing
then only part of the film format
- Straight lines are generally reproduced curved in the picture ("barrel
shaped distortion").
More details to get the explanation:
Imagine yourself standing close to a straight railroad, looking
perpendicularly to the rails through the viewfinder of your single-lens-reflex
camera, having a lens with an angle of view of 180 degrees. You look at the
rails, which are passing diagonally from one corner to the other.
What do you see ?
- It is a subject with two parallell straight objects, the rails.
- They are separated by a certain distance in the middle of the picture.
Lens to subject distance is here typically a couple of meters.
- The distance between the rails diminish to zero at the corners, which
represent a lens to subject distance of infinity.
Realising that this is a correct description of what you see,
you also realise, why the Fisheye lens must have a "barrel shaped distortion",
and why the conventional property of wide angle lenses: "straight lines remain
straight" is impossible for Fisheye lenses. It is evident, why the "barrel
shape" in this case is closer to a realistic reproduction than the "straight
lines remain straight" of other wide angle lenses.
Iit's logical to think, the planes of sharpness also could be
different for Fisheye lenses compared to other wide angle lenses. Conventional
wide angle lenses are designed to reproduce flat subjects well on flat film.
So they must handle a large variation in lens to subject distance, going from
the middle of the picture to one corner . The larger the angle of view, the
more difficult this will be. With an angle of view of 180 degrees, and small
lens-to-subject distance in the middle of the picture, this is impossible. Therefore
Fisheye lenses are designed to reproduce not flat, but Fisheye
lenses curved objects sharply on the flat film surface. It's important clue
to the extraordinary results at underwater photography: the curvature of field
and the reduced lens to image distance, produced by the dome port, is an ideal
situation for the Fisheye lens !
You can take lots of pictures under water with a Fisheye
lens, without bothering about the distortion, the spectators will never notice.
Please see Pictures made by Zenitar
Fisheye lens and Peleng
Fisheye lens at the Picture Gallery.
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