Wide angle, deep field, close focusing optical system

An optical system having the features of a wide angle lens, a deep field lens and a close focusing lens is comprised of an objective lens, a field lens and a relay lens aligned on an optical axis in that sequence for the objective lens to form an intermediate image at or near the field lens and for the field lens and relay lens to transmit that same image to a smaller final image at the plane of the film of a film camera or charge coupled device of a video camera. The objective lens preferably has a fixed focal length and a wide open aperture for forming the intermediate image of a larger size than is otherwise normal for an objective lens of that focal length. Preferably, the relay lens has the iris and focusing mechanism whereby the objective lens and field lens are not required to be used for aperture control and focusing. The optical system provides an extended optical axis for accommodating lighting of a near object being photographed. In modifications of the basic optical system, the optical axis is turned 90.degree. one or more times and rotatable joints are provided in the lens barrel for versatile positioning of the objective lens relative to the camera with appropriate prisms for inverting and reversing the orientation of the final image at the film or CCD detector plane.

This invention relates to an optical system for still or motion picture 
cameras, video cameras or the like and, in particular, is directed to an 
optical system for producing the features of a wide angle lens, a deep 
field lens and a close focusing lens, all in one optical system. 
In many optical imaging applications, such as for cameras and the like, 
there is a need to provide a large depth of field so that objects located 
both near to and far from the camera appear to be in focus to an 
acceptable degree, as well as the actual object focused upon being in 
focus. Further, there is a need to expand the depth of field from an 
object at an optical infinity distance to a near object where the object 
height to image height ratio, i.e. magnification by the optical system, is 
less than ten to one (10:1) and possibly as low as one to one (1:1) or 
less. 
One conventional approach used to achieve a large depth of field comprises 
the use of a short focal length, wide angle lens and stopping down its 
aperture to an "f" number in the range of f/8 to f/16, i.e. substantially 
reducing the aperture size, where said aperture range still provides an 
adequate level of light to obtain an acceptable exposure at the image 
plane for the film in the camera or the charge coupled device ("CCD") of a 
video camera. Because of the requirement for a low magnification ratio, 
the wide angle lens is preferably of a short overall length and the object 
is placed close to the front optical surface of the lens system. Also, 
preferably the overall diameter of the lens system, especially at the 
front, is minimized in order to provide some space and access for lighting 
of the object which becomes particularly difficult for movie cameras which 
are larger than still cameras. Moreover, a short length, small diameter, 
wide angle lens will also have a short back focal length, i.e. the 
distance between the rear of the lens and the image plane. However, the 
back focal length distance must be no less than a certain minimum distance 
because in the case of a reflex film camera that distance tends to be 
large due to the space required for the reflex mirror between the lens and 
the image plane and in the case of a video camera that distance tends to 
be large due to the presence of the necessary beamsplitter optics. Even 
with a compact wide angle lens with these desirable features, the 
closeness of the object to the front face of the film camera or video 
camera would create serious problems in lighting the object, thereby 
making the optical imaging system impractical for actual use in most 
applications. 
For example, in FIG. 1 of the drawings there is a diagrammatic illustration 
of a typical optical system of a film or video camera. A lens 10 is 
mounted on the front face 11 of a camera (not shown) and on an optical 
axis 12 of the camera. If the camera is of a single lens reflex ("SLR") 
type, it will have a reflex mirror 13 positioned at a 45.degree. angle to 
the optical axis 12 inside of the camera and in front of the image plane 
14 where the film will be located. The reflex mirror 13 or other 
mechanism, such as a rotating mirror in a movie film camera or a 
beamsplitter in a video camera, requires space between the front of the 
camera and the image plane 14 of a distance U which limits the minimum 
size of the back focal length of the lens 10. When a close-up picture of 
an object O is desired, there is a limited amount of space, illustrated by 
the cross hatched areas L, surrounding the optical path between the camera 
and the object O that is available for positioning lighting devices for 
lighting the front of the object O that faces the camera in order to 
develop a proper exposure on the film or CCD at image plane 14. As 
discussed above, if the lens 10 is a wide angled lens and the aperture is 
stopped down to attempt to accomplish focusing of both the near object O 
and objects at infinity focal distance, the lighting from the areas L 
becomes even more important and yet the space is very limited because the 
wide angled lens 10 is short in length and must be set at or near the face 
11 of the camera for providing the proper back focal length distance 
between the lens 10 and the image plane 14. These and other problems of 
the prior art are overcome by the present invention. 
An object of the present invention is to provide an optical system with a 
large depth of field for adequate focusing on objects located from and 
between a close focus distance and a relatively large focus distance. A 
further object of the present invention is to provide such an optical 
system wherein the image magnification ratio is less than ten to one 
(10:1). 
Another object of the present invention is to provide an optical system for 
a film or video camera or the like in which an objective lens group has a 
fixed focal length and open aperture for forming an intermediate image and 
a second lens group optically transmits the intermediate image to a film 
or detector plane and forms a final image at that plane of a smaller size 
than the intermediate image to thereby reduce the effective focal length, 
increase the effective field of view and increase the apparent depth of 
field of the objective lens group. Further, it is an object of this 
invention to provide such an optical system wherein the second lens group 
includes a field lens group at or near where the intermediate image is 
formed and a relay lens group nearer the final image, with the relay lens 
having means for focusing the final image on the film or detector plane. A 
further object of this invention is to provide such an optical system 
wherein the relay lens includes means for aperture control. Still further, 
an object of this invention is to provide such an optical system wherein 
orientation correction optics are provided in the second lens group for 
correcting the orientation of the final image by inverting or reversing 
the final image. 
Still another object of the present invention is to provide an optical 
system that extends the objective lens forward of the camera body a 
sufficient distance to provide ease of lighting of objects located at a 
close focus distance with an object to image magnification ratio of down 
to one to one (1:1) or even less. 
A still further object of this invention is to provide an optical system 
for a film or video camera or the like which substantially extends the 
length of the optical axis without adversely affecting the image formed at 
the film or CCD plane for allowing the use of mirrors, prisms or the like 
to change the direction of the optical axis for using an angled and 
rotatable lens barrel for taking unique pictures that would be extremely 
difficult or impossible with a conventional straight lens because of the 
size and location of the camera. 
Other objects, advantages and features of the present invention will appear 
from the following description of the preferred embodiments and the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 2, the optical system 20 of the present invention is 
illustrated in its simplest form as mounted on the front face 21 of a 
camera (not shown), which front face 21 is the same as or comparable to 
the front face 11 illustrated in FIG. 1 of any type of motion picture, 
still or video camera or the like. The lenses of the optical system 20 are 
positioned in a lens cylinder or barrel 22 that is mounted on the front 
face 21 of the camera and throughout this specification and the claims the 
references to "lens", "lenses", "lens group" and "lens means" shall mean 
and include any form of single lens or multiple element lens with or 
without an iris for aperture adjustment and any such lens either can be 
selected from commercially available lenses or specifically created for 
use in the optical system of this invention. An objective lens 23, 
sometimes referred to as a taking lens, is mounted in the forward end of 
the barrel 22 on the optical axis 24 for forming a first or intermediate 
image 25 within the barrel 22 of the object O which, as with the object O 
of FIG. 1, may be positioned close to the front of the lens 23. A field 
lens 27 is positioned behind the objective lens 23 toward the camera and 
the spacing between the objective lens 23 and field lens 27 is such that 
the intermediate image 25 is formed in or near the field lens 27, either 
in front or back of the field lens 27. The intermediate image 25 is shown 
at a distance in front of the field lens 27 in FIG. 2 and other Figures 
only for convenience and clarity of illustration. A relay lens 28 is 
provided in the barrel 22 on the optical axis 24 between the field lens 27 
and the camera for forming a second or final image 29 on the film plane of 
a movie or still camera or the CCD detector plane of a video camera. The 
distance U' between the relay lens 28 and the image plane of the final 
image 29 can be of any desired amount, as those skilled in the art will 
understand, but usually will be relatively large whereby there is adequate 
space for the reflex mirror 30 of the film camera or the beamsplitter of a 
video camera and other elements, as discussed below. The relay lens 28 may 
be a macro lens. 
In the event only a single intermediate image 25 is formed in the optical 
system 20 between the objective lens 23 and the final image 29, the final 
image 29 will be inverted and reversed, and therefore a Pechan prism 31 or 
the like may be provided in the barrel 22 for inverting and reversing 
(reverting) the image to provide the normal orientation of the final image 
29 in the camera. The Pechan prism 31 is preferably of a roof or roof edge 
type but any prism or combination of mirrors that inverts and reverts the 
image be used. As used throughout this specification, "Pechan prism" shall 
mean the preferred roof edge Pechan prism or any optical equivalent. 
In the optical system of FIG. 2, the lens or lens groups 23, 27 and 28 may 
be of normal diameters whereby the diameter of the barrel 22 is relatively 
normal, rather than being very large as required by some special wide 
angle optical systems. On the other hand, the optical system 20 is very 
long along the optical axis 24 whereby there is substantial space, as 
shown by the cross hatched areas L' surrounding the barrel 22, for 
providing lighting of the front of the object O to be photographed even 
though the object O is close to the end of the barrel 22. 
In order to obtain all of the advantages of the optical system 20 of the 
present invention, it is preferred that the lens groups 23, 27 and 28 and 
their positioning be such that the intermediate image 25 formed by the 
objective lens group 23 be larger than the final image 29, which provides 
an increased field of view of the entire imaging system as will be 
discussed more fully below in connection with FIGS. 3-10. Moreover, it is 
preferred that the objective lens group 23 be fixed at infinity focus and 
full aperture for maximizing the field of view and minimizing the problems 
of focusing on the closely spaced object O. Further, it is preferred that 
the field lens group 27 be fixed in the barrel 22 in the desired location 
from the fixed objective lens 23. Still further, it is preferred that the 
relay lens group 28 be provided with an adjustable iris for adjusting the 
aperture and that one or more lenses of the relay lens group 28 be 
adjustable along the optical axis 24 for focusing the final image 29, such 
as by an external adjustment ring assembly 32. By this preferred 
arrangement, the objective lens group 23 may be readily interchanged with 
other objective lens groups selected from commercially available lenses, 
as identified below, or specially constructed lens groups without 
otherwise modifying the optical system 20, similar to the manner in which 
other lens assemblies are interchangeably mounted on the front face 21 of 
a camera. By way of example and without limiting the scope of this 
invention, the objective lens 23 may be a Nikon 20 mm f/4, Nikon 28 mm 
f/2.8 or Nikon 50 mm f/1.4, the field lens group 27 may be any 
multi-element lens with a focal length of about 25 mm to 50 mm and the 
relay lens group 28 may be a Nikon Micro-Nikkor 105 mm f/2.8 or Nikon 
Micro-Nikkor 200 mm f/4 (although a field lens group 27 with a longer 
focal length, perhaps 100 mm, is preferred when the relay lens group has a 
200 mm focal length), all of which have been tested successfully in this 
optical system. One specific combination that has been tested successfully 
is a Nikon 50 mm f/1.4 lens as the objective lens 23, a 50 mm field lens 
as the field lens 27 spaced at about the focal length from the objective 
lens 23, and a +4 diopter attachment and Micro-Nikkor 105 mm f/2.8 as the 
relay lens 28 spaced 3.25 inches from the field lens 27, with the aperture 
of the relay lens set between f11 and f16. It may be advantageous to use 
an objective lens having a focal length less than 20 mm, which has not 
been tested, but at present it seems unlikely that normally it would be 
advantageous to use an objective lens 23 having a focal length of greater 
than 50 mm. Also, a zoom lens may be used advantageously as the objective 
lens 23 and may be either a continuously variable focal length type or a 
multiple discrete focal length type, with an appropriate field lens 27, 
for conveniently selecting a desired focal length without changing lenses. 
The overall length of the optical system 20 can be substantially increased 
or decreased by the particular selection of the relay lens group 28 such 
as, for example, by using a 200 mm focal length relay lens 28, the optical 
system 20 will be about 18 inches to 24 inches long, depending on the 
other lens groups, which is longer than a system using a 105 mm focal 
length relay lens. 
Referring now to FIGS. 3-6, the principle by which the effective field of 
view is increased by the optical system of this invention will be 
described in connection with a conventional 35 mm movie film 35. The movie 
film 35 illustrated in FIG. 3 is of the common four perforation type 
wherein the film is advanced downwardly in the direction of arrow 36 a 
distance of four perforations for each picture frame 37. By cinematography 
industry standards, the center line 38 of the picture frame 37 is offset 
from the center line 39 of the film 35 by 0.050 inches to provide space 
between the picture frame 37 and the perforations 40 along one side of the 
film 35 for a sound track 41. The typical industry standard size of the 
picture 37 is a height H of 0.735 inches and a width W of 0.868 inches. In 
the top or plan view FIG. 4, the film 35 is shown immediately behind an 
aperture plate 42 having an aperture 43 of the width W, i.e. 0.868". With 
an objective lens 44 having a focal length F in a conventional optical 
system, the field of view angle A which the objective lens 44 can transmit 
to the film 35 is limited by the mathematical relationship between the 
focal length F and the aperture and picture width W which is expressed by 
the following formula: 
##EQU1## 
Assuming the objective lens 44 has a relatively common 50 mm focal length 
F and the width W is 0.868 inches, as described above, the angle A of the 
field of view is 24.86.degree. according to the above formula and as shown 
in FIG. 4. In other words, the field of view of a 50 mm objective lens in 
a conventional 35 mm movie film optical system is limited to 24.86.degree. 
in the horizontal direction, which is only 12.43.degree. on either side of 
the optical axis 12 and objects beyond that field of view will not be 
reproduced on the film picture 37 because they will be beyond the width W 
of the aperture 43 even if the iris in the objective lens 44 is fully 
opened. Obviously, the "field of view" in the vertical direction is even 
more limited because the height H of the film frame 37 is less than the 
width W. 
In the top plan view FIG. 5 of a portion of the optical system of the 
present invention, the objective lens 23 is again assumed to be a lens 
having a focal length F of 50 mm but here, unlike a conventional system, 
the objective lens 23 forms the intermediate image 25 of a larger width W' 
of any desired size because the size is not limited by the picture frame 
width and aperture width W. By way of example, without limiting the scope 
or application of the present invention, the intermediate image 25 may be 
formed with a width W' of 11/2 times the width W. In other words, width W' 
equals 1.302 inches (0.868+0.434) and the field of view angle A' of this 
intermediate image 25 is again a mathematical function, according to the 
above formula, of the focal length F of 50 mm and the width W' of 1.302 
inches, namely, the angle A' is 36.54.degree.. In other words, in this 
example, the field of view at the intermediate image 25 of the optical 
system of the present invention is nearly 12.degree. or 50% larger than a 
conventional system even though the same 50 mm objective lens is used. 
This larger intermediate image 25 is then transmitted by the field lens 
group 27 and relay lens group 28 to form the same image as the final image 
29 but of the smaller width W. This creates the effect illustrated in FIG. 
6 of having an objective lens 23' in a conventional system, such as shown 
in FIG. 4, that produces an image of the width W but has a field of view 
angle A' (36.54.degree.) whereby the effective focal length F' is only 
33.4 mm, which again is calculated by the above formula. By increasing the 
effective field of view of the objective lens in the optical system 20 of 
this invention, the background visible beyond the closely positioned 
object O is substantially increased and yet the close object O and the 
background are both in focus thereby producing the effect of a 
substantially increased depth of field by the optical system 20. In 
effect, the optical system 20 simulates a wide angle lens system with 
improved depth of field of focus which has been observed by photographing 
a small object O located a short distance from the objective lens 23 with 
that object O in focus as well as objects at a relative large optical 
distance, up to infinity, being in focus. 
Referring now to FIGS. 7-10 which are similar to FIGS. 3-6, respectively, 
but illustrate the use of 35 mm film in a still camera and the comparison 
between a conventional optical system and the optical system 20 of the 
present invention. In a still camera, the 35 mm film 35' is advanced in 
the horizontal direction of arrow 36' in an amount equal to eight 
perforations 40' for each picture frame 37'. Although the film stock for 
motion picture film 35 and still camera film 35' may be identical, the 
picture frame 37' of a still picture is centered on the center line 38 of 
the film and has a width SW of 1.485 inches and a height SH of 0.991 
inches. In other words, the width SW of a still picture frame 37' is 
slightly larger than twice the height H of a movie picture frame 37 and 
the height SH of a still picture frame 37' is slightly larger than the 
width W of a movie picture frame 37. Referring to top plan view FIG. 8, 
the film 35' moves behind the aperture wall 42' having an aperture 43' of 
a width SW, that is, the width of the picture frame 37'. Again, with a 
conventional objective lens 44' having a focal length F in this still 
camera arrangement, the field of view angle SA has the mathematical 
relationship to the aperture/film width SW and the focal length F, as 
follows: 
##EQU2## 
Assuming the focal length F of the objective lens 44' is 50 mm (the same 
as in the illustration of FIG. 4), the field of view angle SA will be 
41.33.degree. which is larger than the movie film example of FIG. 4 
because the aperture/film width SW of still film is larger than the 
aperture/film width W of movie film. Referring to FIG. 9, if an objective 
lens 23 of the optical system 20 of this invention having a focal length F 
of 50 mm is used to produce an intermediate image 25 of a width SW' of 
11/2 times the width SW, then the field of view angle SA' of this 
intermediate image 25 equals 50.90.degree. which is 17.57.degree. larger 
than field of view angle SA. Referring to FIG. 10, which is similar to 
FIG. 6, this expanded field of view angle SA' of 58.90.degree. produces an 
image of the width SW as though the objective lens 23 has a focal length 
F' of 33.4 mm. Again, as with the example of the movie film application of 
FIGS. 3-6, the effective focal length of the objective lens 23 of the 
optical system 20 of this invention is reduced by about one third to 
create the effect of a wider angle lens than is actually used as the 
objective lens and an apparent increase in the depth of field. 
Referring now to the modification of the present invention shown in FIG. 11 
which diagrammatically illustrates the optical system, generally 
designated 50, without the normal surrounding barrel, such as barrel 22 of 
optical system 20 in FIG. 2. From the front end of the optical system 50 
closest to the near object O to be photographed, the optical system 50 
includes an objective lens 53 for forming an intermediate image 55 that is 
transmitted by a field lens 57 through an Amici prism 63 to turn the 
optical axis 54 90.degree. for the light radiation to pass through a relay 
lens 58 to the reflex mirror 60 to form the final image 59 in the camera 
behind the face 51. The objective lens 53, field lens 27 and relay lens 58 
may be the same as the objective lens 23, field lens 27 and relay lens 28 
of optical system 20. Essentially, the optical system 50 is the same as 
the optical system 20 of FIG. 2 except for the inclusion of the Amici 
prism 63 for deviating, bending or turning the optical axis 54 by 
90.degree.. The Amici prism 63 is provided with a roof edge and also 
serves to invert and revert the image whereby the Pechan prism 31 provided 
in the optical system 20 for inverting or reverting the image is not 
needed in the optical system 50. By this arrangement the camera can be 
oriented at 90.degree. to the direction of the object O for obtaining 
special photographic effects, such as being able to photograph a small 
object O sitting on the ground or floor. Again, because of the length of 
the optical axis 54, even though it is turned 90.degree., there is 
adequate space, shown by the cross hatched areas L' and L", for lighting 
the near object O positioned close to the objective lens 53. In fact, the 
area L" directly below and on the sides of the lens system is not limited 
by the camera. 
Referring now to the modification of the present invention shown in FIG. 
12, the optical system, generally designated 70, is substantially similar 
to the above-described optical systems 20 and 50 illustrated in FIGS. 2 
and 11, respectively. On the optical axis 74 from the object O to the 
final image 79, there is provided an objective lens 73 (like objective 
lens 23 and 53) forming an intermediate image 75 that is transmitted 
through a field lens 77 (like field lens 27 and 57) to a fold mirror 84 
that turns the optical axis portion 74a by 90.degree., shown as optical 
axis portion 74b, to another fold mirror 85 that turns the optical axis 
another 90.degree., shown as optical axis portion 74c, which is in a plane 
parallel to the plane of the optical axis portion 74a. Along the optical 
axis portion 74c there is provided a first Pechan prism 81a, a second 
Pechan prism 81b and a relay lens group 78 to transmit the light to the 
reflex mirror 80 and form the final image 79 in back of the face 71 of the 
camera. The fold mirrors 84 and 85 may also be mining prisms. The barrels 
for containing the optical system 70 are provided with rotatable joints, 
which will be described in connection with FIGS. 14 and 15, at fold 
mirrors 84 and 85 to allow the barrel enclosing optical axis 74a to be 
rotated about the optical axis 74b as shown by the arrow R and for the 
optical axis 74b to be rotated about the optical axis 74c as shown by the 
arrow R'. The Pechan prism 81b is mounted in the barrel in a fixed 
position with respect to the face 71 of the camera to invert the image to 
be formed as the final image 79, which is the same function performed by 
the Pechan prism 31 described in connection with the optical system 20 of 
FIG. 2. The Pechan prism 81a is rotatable about the optical axis 74c, as 
shown by arrow R" for correcting the orientation of the final image 79 
caused by rotating the barrels in the directions of arrows R and R'. By 
this optical system 70 of the invention, the versatility of the different 
positions of the camera and the objective lens 73 is greatly increased and 
the optical system has the ability of being rotated in one or both of the 
optical axes 74b and 74c to follow a moving object without moving the 
camera merely by guiding the barrel surrounding the optical axis portion 
74a to follow the object. Again, the length of the optical axis 74 
provides space, shown by the cross hatched areas L' for lighting the front 
of the object O, as with the previously described embodiments of this 
invention. 
Referring now to FIG. 13, an optical system 70' is shown that is 
substantially the same as the optical system 70 of FIG. 12 and components 
of the optical system 70' that are the same as the optical system 70 will 
be identified by the same numerals with a detailed description thereof 
being omitted. The differences between optical system 70' of FIG. 13 and 
optical system 70 of FIG. 12 is that the Pechan prism 81b for inverting 
the final image 79 is omitted and folding mirror 84 is replaced by an 
Amici prism 83, similar to Amici prism 63 in the embodiment of FIG. 11, 
for inverting the final image 79. This simplifies the optical system and 
reduces its cost without sacrificing the versatility of the optical system 
70 illustrated in FIG. 12. 
In each of the modifications of the present invention shown in FIGS. 11, 12 
and 13, the folding mirrors and prisms may be located anywhere along the 
optical axis of the system and various types of equivalent optical 
elements may be used for accomplishing the functions of these mirrors and 
prisms, as well as the functions of the lens groups. 
Referring now to FIGS. 14 and 15, a simplified exterior view is shown of 
the lens cylinder or barrel assembly, generally designated 90, which is 
adapted to contain the optical system of this invention, as shown and 
described with respect to FIGS. 12 and 13, wherein there are two 
90.degree. bends or deviations in the optical axis 74 of the optical 
system. The lens barrel assembly 90 includes the objective lens group 73 
which is detachably connected to the face 91 of a first barrel section 92 
containing the folding mirror 84 of the optical system 70 or the Amici 
prism 83 of the optical system 70'. A second barrel section 93 containing 
the folding member 85 of optical system 70 or 70' is rotatably connected 
by a flange 94 to a flange 95 on the first barrel section 92 for allowing 
rotation about the optical axis portion 74b, as shown by arrow R in FIGS. 
12 and 13. A lock mechanism 96 may be provided for selectively locking the 
tubular sections 92 and 93 against relative rotation. Similarly, a 
selectively operable rotation joint 97 is provided between barrel section 
93 and a third barrel section 98 of the barrel assembly 90 for allowing 
selective rotation of tubular section 93 about the optical axis portion 
74c as shown by arrow R', in FIGS. 12 and 13. The relay lens 78 is 
provided at the base of barrel section 98 adjacent the camera face 71. The 
field lens 77 can be provided at any convenient location in the barrel 
assembly 90 and is not shown. An external adjustment ring 99 may be 
provided on the barrel tubular section 98 for adjusting the angular 
position of an internal element, such as the Pechan prism 81a (not shown). 
Other conventional devices and adjustments may be provided in the barrel 
assembly 90, such as a removable filter 100. The shape, diameter, etc. of 
the barrel assembly 90 is unimportant to this invention except to the 
extent that it must accommodate an optical system, such as the optical 
systems 70 and 70' described above, and provide all of the degrees of 
motion and adjustment that may be required. For example, the barrel 
portion 98 could be much shorter and a lengthy barrel portion provided 
between the barrel portions 92 and 93 or the barrel portion 92 could be 
much longer with a shorter barrel portion 98. 
Although a specific embodiment of the present invention has been described 
with several variations and modifications, including specific prisms and 
lenses, it is to be understood and will be appreciated by those skilled in 
the art that the present invention may be practiced by using various other 
components and elements in different arrangements for accomplishing the 
same functions as this wide angle, deep field, close focusing optical 
system.