Lenses & filters
Kodak Lenses and Shutters Product booklet
Product booklet for Kodak Lenses and Shutters. 50 pages in English. Read the original PDF, download or print a copy without registration.
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- Kodak Lenses and Shutters
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www.orphancameras.com tENs
SPECIFICATIONS
Kodok Ektors
Ektar ff63,I4-inch
Poge 34
tktar {s.7, lo7-rnm.
Pcge 35
Ektar {2.9, 45-mrn. rrlr$il$&$IIUTTilB$Pcge 36
TnB Eastman Kodak Company has manufactured its Ektor f/3.5, 50-mm.
own lenses for many years, and there has grown in its Poge 37
organization a large group of experts of long experience
and great skill. It is this fact which accounts for the out- Kodsk Anostigmofs
standing position of the Company among the world's
manufacturers of lenses. The real value of a lens can be l/?.5, f/4.5 ("35")
judged only by its performance, and on this basis Kodak Puge 38
lenses hold an unexcelled position in the particular fields f/5.6 ("35" ond Bonlorn)
fcrvhich they are designed. Poge 39
Modern photographic lenses and shutters of high qual-
ity rcpresent the most perfectly developed stage of optical f/4.5 fBonrom)
and mechanical skill. The production of a good lens Pcge 4O
reciuires the co-operation of many experts, each of whom f/t.s (Dvo Six-Zo)
is selected after many years of training and painstaking Poge4l ,: t:
experience: lens designers who apply their knowledge of
rnathematics and geometrical optics to the calculation of f/4.5 (Recomor l8)
the shapes and arrangements of different kinds of glass Poge 42
which go to form a lens; technicians and craftsmen who ff4.5 {Reromcr 33)
grin.l and polish the glass and assemble it to a finished Poge 43
lens; physicists and optical experts who work in conjunc-
tion with the designers of the lens and camera, and who f/4.5 Seeciql II
ccntrol the optical quality of the finished product. Pose 44 I 6ZO ona
The shutter is important both because it times the expo- U4.s \ 616 Kodsks
sure and because its case must maintain the spacing and Pose45 |
alignment of the lens elements. Successful shutter design
' depends on the application of the knowledge of physicists ry5.9 I czoo'a
and ergineers, and on the skiil of experienced craftsmen. Pnge 46 l 615 Ksdakr
Here again, as in the case of lenses, the Eastman Kodak r/4.5,5- to I2-inch
Company has attained an outstanding position. ?aga 47
In order to meet the high standards required of photo-
. graphic lenses and because of the specialized nature of the f/7.7,$-inch ,
Pcae 49 '::i;
Lens Dimenrions
o "Winler Paltern" takenw'ith a Kod,ak Poge 5O
Recomar33, Kodah Anustigm.otfl+.5.
Proieclion Lenreg
for Fnlorging
Pcge 5l
)View original page 2Page 3 · Read text
o Spec'ialKodak lens types-Long f ocus,w'idea'perture,w'id,eangle.
work involved, the Eastman Kodak Company maintains a separate
factory devoted to the production of optical work of the highest pre-
cision. Lenses and lens mounts for every purpose are designed here,
and models of them are made and tested; from these models, lenses
are made for use on cameras of Kodak manufacture. {
A SHORTHISTORYOF PHOTOGRAPHICLENSES {
Dunrxc the 100 years in which photography has been practiced, lens
design has reached a remarkable degreeof advancement. The earliest
"landscape" photographs were taken with a single meniscus lens,
with a small stop or diaphragm situated a short distance in front of
the concave side of the lens. The speed of this lens was only about
fl12, but it had surprisingly satisfactory covering power over the
50o field normally demanded of it. This lens, first designed by
Wollaston, is still manufactured in large quantities for simple
cameras, for which it is entirely satisfactory. Such lenses are not
used at greater apertures, becausethe quality of the image would be
spoiled bry several aberrations. These are (1) Spherical aberration,
which gives a very slight blurring or hazinessof the definition over
the entire picture. This defect becomes rapidly greater with in-
creased aperture, and is the factor which prevents the use of this
type of lens above about f ll2. (2) Astigmatism, which makes the
image decidedly unsatisfactory beyond the 50o field. Astigmatism
could be removed by changing the shape of the lens, but only with
the result that the field becomes curved. Since photographs are
practically always made on a flat film, it is clear that a flat field is
essential, even though it involves the introduction of some astigma-
tism into.the outer parts of the image.
t*aD
B,
EIi,View original page 3Page 4 · Read text
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When portrait photography was attempted around 1840, the low
speedof the landscapetype of lens was a great limitation, so, in that
year, the famous Petzval Portrait Lens was designed.This had the
remarkable speed of f13.5, but the construction was such that com-
plete flattening of the field was impossible, even if considerableastig-
matism were permitted. This type of lens therefore will not cover a
field of more than about 20", and for critical delinition, 10orepresents
about its limit. Nevertheless,for projection and some other purposes
where a 10o field is adequate, the Petzval type of lens is still exten-
sively used, at apertures up to fll.6.
Further attempts to discover a type of construction intermediate
between the landscape lens and the portrait lens revealed the fact
that types with good covering po\^,.ercould be made to operate only
at small apertures. A compromise was the Rapid Rectilinear l-ens,
designed in 1866, which at Jl8 covered a 45" field reasonably u'ell
before the inevitable astigmatism began to spoil the image.
Optical theory was advancing rapidly during the latter part of the
last century, and in 1880,it was realizedthat the elimination of astig-
matism with simultaneousflattening of the field would be much sim-
plified if optical glass of high index and low dispersion could be
obtained. By 1888,this problem had been solved by the introduction
of barium crown glass having just the desired properties. This led
to a great burst of activity in the design of lenses,and within 15
years, a considerablenumber of entirely new lens types had appeared,
in all of which the possibility existed of flattening the field with
simultaneous removal of astigmatism. Such lensesreceived the name
"anastigmat," although some of the types were so unpromising and
were so poorly designed that pictures made by them were no better
than those made by a good rapid rectilinear lens.
The early anastigmats worked at low apertures, and for many
yearsy'S was considered a fair speed for general use. But, gradually,
the unsuitable types were eliminated, and good types were worked
out more fully, so that by 1914,f 14.5had become the normal speed
of a good lens. Since 1920,f13.5 has become common, andrecently,
by following up some of the early types in greater detail, fl2 and
even faster lenses have been made for miniature cameras, all of
"normal"which cover satisfactorily the field of 50". The Kodak
Ektar fl2, 50 mm., is an excellent example of a modern miniature
camera lens. In cin6 lenses,because the field is ordinarill' onl1. f 50
in size, the larger apertures are achieved more easily.View original page 4Page 5 · Read text
7
IENS PROPERTIES
THEORETICALLIMITSOF DEFINITION
THn structure of light itself imposes a limit to the definition of a
theoretically perfect lens. The simple geometric theory of light
would indicate that the smaller the aperture, the better the defini-
tion. Actually, this is not the case,and the wave theory of light indi-
cates that the larger the aperture, the better the definition. Due to
the structure of light waves, a beam of light in passing through a
small aperture does not continue unchanged but spreads slightly at
the aperture edges. This behavior is analogous to the spreading of
water waves after passing through a small opening in a breakwater.
As a result of this spreading of light, or diffraction, the image of a
point of light is a small blur, for a theoretically perfect lens. The size
of the blur is decreasedas the aperture is increased, as light waves
coming from various parts of the aperture reinforce each other at the
center of the image, but cancel out in its outer portions. This inter-
ference effect depends on ivave length as well as the size of the aper-
ture. Trn'o such images which are very close together may merge and
be indistinguishable.As the,size of blur is decreasedby increasing
the aperture, the two images become smaller and appear separate,
"resolving or are resolr.ed.The term power" refers to the ability to
create separate images of points in the subject which are close
together. A textbook on physical optics should be consulted for a full
explanation of this matter.
The relation between resolving power for points, effective lens
diameter, and wave length is stated thus: a:1.22)\ L
where a is the angular separation of two points just resolved
where \ is the wave length of light
and L is the effective diameter of the lens.
Therefore, the angular resolving po$-er for two distant points is the
same for all theoretically perfect lenses of the same effective diame-
ter, regardless of relative aperture. It also follows that the linear
separation of images just resolved in the focal plane is proportional
to the /-number of the aperture regardless of effective diameter.
Thus, for theoretically perfect lenses, the wider the relative aper-
ture, the higher is the resolution and the finer is the detail resolved
in the aerial image. In the case of telescope lenses, this is achieved
in practice; consequently, large telescope lenses have a resolving
power, can tolerate magnification, and shorn-detail in proportion toView original page 5Page 6 · Read text
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their apertures. It is for this reason that astronomers make larger and
larger telescopes. But, in the case of a telescope lens, only a very
small fieklis used, the stars observed being usually at the very center
of the field. \\Ihen a lens is made for a camera, however, it must have
a wide field in order to give a picture of appreciable size, since other-
wise the focal length would be too great and the camera very clumsy.
A lens cannot be made to give a theoretically perfect image for a
wide field and, in practice, the resolving power of a photographic
lens is determined by a balance between the residual lens aberrations
and the aperture.
Resolving power measurements are not as significant as the
appearance of an artilicial star image examined with a microscope
on a lens bench. This image gives more detailed information as to the
nature and extent of the residual aberrations and thus of the quality
and performance of the lens.
THE ABERRATIONS OF A LENS
Ir might be of interest to know something of the various shortcomings
which render an ordinary biconvex lens useless for photographic pur-
all of which must be correctedin a photo6raphicobjective.FBfffl trnfl
A single biconvex lens cantnilnulllfliltfflbe used to formlll]J0ran flftfrtrimage, r]ll|[but it willtlltfbet0llililt0$tlffitt0lllil0rations." If the paths \r-ere calculated for a number of oblique
rays
of light through thisffill0illiltlens from aill]fllilflililtilltdistant point situated0ttllffirnliloff to oneilflflilt|l|l|l1!ffi
l l
I l Il
i
i i
' '
fromthe ideali*.g" p.,ririon..,-,t" ,r.r,,r-turlr"J., lollo*rt
(I) Sphericol Aberrolion: If this defect is present, the various rays
from a single zone of. the lens intersect at a point or-rthe middle
ray of the beam, but the rays from different zones cross at dif-
ferent distances from the lens. The effect of a small amount of
this aberration on the image of an extended subject is to cover
it rvith a haze of light. If present in large amounts, spherical
aberration may spoil the sharpness and crispness of definition,
approximatelyilileonorfrrra0tilt$if fillffrfiil{]ilhennrnequniformlynr^crrcc."i'*-el.rilsilillyilsesover the wholefrnrrhleqnrneruillfllyfield.ilrlttllilileffiefAsatrd thehardcrmagni-leilsfnView original page 6Page 7 · Read text
their apertures. It is for this reason that astronomers make larger and
larger telescopes. But, in the case of a telescope lens, only a very
small f,eldis used, the stars observed being usually at the very center
of the field. When a lens is made for a camera, however, it must have
a wide field in order to give a picture of appreciable size, since other-
wise the focal length would be too great and the camera very clumsy.
A lens cannot be made to give a theoretically perfect image for a
wide field and, in practice, the resolving power of a photographic
lens is determined by a balance between the residual lens aberrations
and the aperture.
Resolving power measurements are not as significant as the
appearance of an artificial star image examined rn'ith a microscope
on a lens bench. This image gives more detailed information as to the
nature and extent of the residual aberrations and thus of the quality
and performance of the ler-rs.
THE ABERRATIONS OF A LENS
Ir might be of interest to know something of the various shortcomings
which render an ordinary biconvex lens useless for photographic pur-
poses, and all of which must be corrected in a photographic objective.
A single biconvex lens can be used to form an image, but it will be
"aber-found to suffer from the following seven major defects called
rations." If the paths were calculated for a number of oblique
rays of light through this lens from a distant point situated off to one
side of -the lens axis, the possible kinds of departure of these rays
from the ideal image position can be summarized as follows:
(t) Sphericol Aberrotion: If this defect is present, the various rays
from a single zone of the lens intersect at a point on the middle
ray of the beam, but the rays from different zones cross at dif-
ferent distances from the lens. The effect of a small amount of
this aberration on the image of an exter-rded subject is to cover
it with a haze of light. If present in large amounts, spherical
aberration may spoil the sharpness and crispness of definition,
approximately uniformly over the whole field. As the magni-
tude of this aberration usually rises rapidly with increased lens
aperture, it becomes progressively troublesome and harder to
eliminate as the speed of a lens is increased
(2\ Como: Coma is a kind of lateral spherical aberration. In spheri-
cal aberration itself. the various zones of a lens suffer from aView original page 7Page 8 · Read text
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longitudinal difference of focus; in coma, the rays from the
various zones strike the image plane at different distances from
the center. Thus in the presence of coma, a single point in the
subject is imaged as an arrowhead pointing radially toward the
center of the field or outward from it.
(3) Astigmotism: In this aberration, a single point in the subject is
imaged not as a point but as two mutually perpendicular short
focal lines, one line being closer to the lens than the other. One of
these lines is in a direction tangential to the field, and the other
is radial and points toward the middle of the picture. The
longitudinal distanc'e from one of the lines to the other is a
measure of the astigmatism present in the lens. Neither coma
nor astigmatism exists at the center of the picture.
(4) Curvqlure of Field: If the positions of the two astigmatic line
images formed by u lens having astigmatism \,'ere to be com-
puted for a number of subject-points lying in the same plane, it
would be found that all the tangential lines lie on one image sur-
face and the radial lines on another. Since astigmatism does not
exist on the lens axis, these two image surfaces coincide in the
center of the picture, but are separate in the outer parts if as-
tigmatism is present. When these image surfaces are flat or al-
most flat, the lens is said to have a flat field, which of course is
necessary if the image is to be rendered as sharply as possible
on a flat film.
(5) Distorfion:When a lens has distortion, the magnification is dif-
ferent in different parts of
o To d,etermi,nethe quality of the image produ.ced' the field. This results in a
by a lens, the image of an arl,ificial star is ex-
amined at a magni.fiailion of zoo lirrtes. distortion of the image, for
instance, causing a square
object to be imaged as a
barrel-shaped or cushion-
shaped figure. When dis-
tortion is present,a straight
line running acrossthe cen-
ter of the picture remains
straight, but straight lines
lying in the outer parts of
the image field are curved
as shown on page 9.
8
i'4View original page 8Page 9 · Read text
(6) Chromqtic Aberrolion: Becausethe degree of refraction or bend-
ing of a ray of light by u polished glass surface varies with the
color of the light, it is clear that every property of a lens varies
with color. Thus the position of the image itself changesslightly
r,r,-iththe color or wave length of light, this effect being known
as chromatic aberration. Fortunately, it is possible to eliminate
this defect by using two or more different kinds of glass in a
lens, and within recent years, a sufficiently wide variety of
optical glasseshas become available to enable any type of lens
to be properly achromatized.
SUBJECT DISTORTED IMAGES ffiffiffiDISTORTION CHROMATIC ABERRATION
rF{EsuBJEcr ,t 'ot'iI"'S?::?ll'.o$.", ,.^.= ro rHE RrqHr.
ALL ABERRATIONS ARE sI{OWN GREATLY EXAGGERATED.
IF- (7') Lolerol Color, or chromatic difference of magnification. In this
I aberration, the focal length of the lens varies from one color to
another, hence, the size of the image in one color differs from its
size in another color. If present, this aberration results in colored
fringes su.rrounding the images in the outer parts of the field. In
9iView original page 9Page 10 · Read text
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black-and-white photography, these colored fringes appear as a
slight blur or f"uzziness,but in color work, especially if the lens is
used in an enlarger, colored fringes may show up very badly. For
this reason, Kodak lenses, according to their intended purposes,
are adequately corrected for this aberration.
"Look'ingo Down on,Rio" lrtken,u'ith,a l{o. 34 Koduk Anust.igntutf l+.5.
1 0View original page 10Page 11 · Read text
IENS PERFORMANCE
A rnxs of even the highest quality is incapable of imaging a point
sourceof light as a geometricalpoint. Instead, such a point is imaged
as a small blur with a very bright center and with the brightness
falling off away from the center. The size of such an image naturallv
cannot be measuredPrecisely.
DEFINITIONAT VARIOUS APERTURES
The character of such a point image changes slightly for different
apertures, but is such for good lensesthat they perform satisfactorily
at all the apertures provided. There is, however, a slight difference
in performance on changing the aperture, apart from depth of field
and lens speed changes. Decreasing the aperture from wide open
generally improves definition slightly, and removes the slight haze
caused by residual spherical aberration. This haze disappears for an
aperture decreaseof one full stop* or less, and a slight increase in
image contrast results. Definition generally improves in the center
of the picture for the first full stop decrease,but remains unchanged
by further decreaseuntil f 116 is reached. Definition away from the
center is slightly improved by decreasing the aperture further to
about two stops from the maximum. Usually there is little changeon
further aperture decrease,except for a continued gain in depth of
field. However, when f.ll6 is reached, a slight decreasein definition
sets in, due to the wave nature of light.
The question arises, especially in miniature camera work, how
small an aperture can be used without loss of definition. For all
apertures normally available, that is, fl22 or larger, the limiting
definition in the case of good lenses is imposed by the type of film
and not by the lens. This is true even for negative films of highest
quality. An aperture of fl22 or fl16 may limit definition in the case
of a slow-copying film of high resolution, such as Kodak Micro-File.
Hence, Jlll or fl8 may be preferable.
The use of enlarger lenses at their smaller apertures may limit
print definition in extreme enlargements,but not in ordinary work.
It must be repeated that these small changes in performance
with aperture are of little consequence.These effects on definition
are much smaller than those due to slight errors in focusing judg-
ment and to slight camera motion.
*-E*. f.o- f l2.o to.f 12.8,or f l4.s to f 16.3.
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CIRCLEOF CONFUSIONAND DEPTHOF FIETD
Wnpnx a lens is focusedfor a certain distance, objects atthat distance
only are sharpest. Objects at all other distances are more or less out
of focus, and points outside of the plane focused upon are imaged
"circlesas blurred circles which are referred to here as of confusion."
The farther the points are from the plane focused upon, the larger
the circles of confusion and the greater the out-of-focus effect.
For critical definition or sharpness,the circle of confusion ,in tlte
print should not be larger than UI00 inch if the print is to be viewed
at the normal viewittg distance of 10 inches, or, oil an angular basis,
the circle of confusion should not subtend more than two minutes
of arc at the eye when the print is viewed for correct perspective
(i.e., when the viewing distance is equal to the focal length of the
camera lens times the amount of enlargement, if any). When the
circles of confusion exceed these limits, they appear to the eye as
small blurs rather than points, and details within the image no
longer appear sharp.
The depth of field of a lens refers here to the range of distances on
the near and far sidesof the plane focusedupon, within which details
are imaged with acceptable sharpness in the final print. Depth of
field increaseswith increasing subject distance, decreaseswith in-
creasingrelative aperture, and increaseswith decreasingfocal length,
other things being equal. Depth formulas are on pages 40 and 41 .
In addition to the factors mentioned above, the depth of field for
any lens is dependent upon the size of the circle of confusion which
is considered as acceptable. In computing the depth of field for
Kodak lenses,a circle of confusion of U200 inch is used for folding
Kodaks, 1/500inch for miniature Kodaks, and 1/1000inch for Cin6-
Kodaks. For the Kodak lensesintended for commercial, press, por-
traiture, and studio work, a circle of confusion approximately equal
to 112000of the focal length is
o The d,epend,ab,il,ity of Kodak shutters ,is used in computing the depth of ,inspectiondue in part to the careful of
each port as it ,is assembled. field. This is a smaller circle than
is usually used in computing
depth of field tables for such
lenses and is for critical defini-
tion when the print is viewed for
normal perspective.At the limits
of the range of sharpness, the
circles of confusion are of the
T2
Digitally signed by mike butkus
DN: cn=mike butkus,
o=orphancameras, ou=29, mike butkus email=mike@butkus.org, c=US
Date: 2017.07.05 13:10:52 -04'00'View original page 12Page 13 · Read text
above dimensions, and between the limits, the circles of confusion
are smaller. In the plane focused upon' these circles areaminimum'
Depth of field tables so computed for each lens are in the specifica-
tion, pages 34 to 49.
o Direct-ztision optical viezuf'nders, as used on the Kod'ah
Bantams, Retinai, Duo Six-zo's, etc., consist of a strong^
negative iens, Lr, which forms a airtual image in front.of
thi tens. urri a weah bositiz,elens, Lz, which pluces this
ztirtual image about 5-feet ahead of the camera.
f=-IMAGEOBJ ECT IMAGE
BY Lr& L2 BYLI
DEFINITIONAND CAMERA TECHNIQUE
Poon definition in negatives is most often due to faults in camera
har-rdling, in particular, camera motion and focusing error. Small
cameras are not held sufificiently steady by the average person for
longer than 1/50 to 1/100 second,nor large hand cameras for longer
than 1/25 second. While the use of a good tripod eliminates camera
motion, in many casessuch use is inconvenient.
When a tripod is not available or its use not convenient, it is
recommended that shutter speedsof 1/25 second or less be used for
large cameras, and 1/50 or preferably 1/100 second for small cameras'
if light conditions permit. Camera motion can be reduced by the use
of a cable release,since the camera rrray be gripped firmly rn'ith both "trigger hands. To release a shutter properly involves a squeeze"
and care should be taken to avoid hand motion. Holding the breath
at the instant of exposure often helps.
Focusing error may be minimized by the proper use of coupled
range finders, or separate range finders. The acquiring of ability for
precise estimation of distance is also desirable. For all close-ups,the
distance cannot be estimated with sufficient accuracy, but must be
measured either with a range finder or a suitable rule or tape. A
general knowledge of depth of field should also be applied in securing
good definition throughout the subject.
1 3View original page 13Page 15 · Read text
MANUFACTUREOF KODAKLENSES
IENS DESIGN
Ir is not commonly realized that lens design is a very long, tedious,
and complicated process requiring months or even years. Briefly, it
comprises the following operations: First, the designer must decide
the type that is to be used, based usually on previous experience.
A likely form must then be worked out, which is tested trigono-
metrically by much numerical computation to determine its defects.
The design is then altered, and the corresponding changes in the
various lens defects (aberrations) are ascertained. On the basis of
these changes, further alterations in the lens construction are then
attempted, until eventually a formula is reached which is satisfac-
tory in all respects. In the course of a design, a number of different
combinations of optical glass types mav be studied before an accept-
able design is reached. In the design of each camera of Kodak manu-
facture, a lens and shutter are often developed at the same time.
TESTING NEW IENS DESIGNS
WnBN a new design has been completed, a sample is made with the
utmost care and tested in every possible way. First the lens is used to
form an image of a distant point source, and the image is examined
on an optical bench at a magnification of about 200 times. The lens is
tilted about its nodal point during the test so that the quality of
definition over the entire flat field can be examined. The lens is next
used to take photographs of various outdoor and ir-rdoor test objects.
A photographic test provides a permanent record of the performance
of the particular lens, and it is also valuable as it reveals any ghosts
and flare spots due to internal reflections from the polished glass
surfaces. If the lens has a focusing mount, the accuracy of the focus-
ing scale is also checked by actual photographic tests. Faster lenses
intended for use on enlargers must also be tested and if necessary ad-
justed to remove lateral color. This is because enlargers are becom-
ing more and more commonly used for making three-color separa-
tion negatives, and noticeable chromatic difference of image size
will ruin the color prints so produced.
Other properties of the lens are also examined, such as its light
transmission, the uniformitl' of illumination over the field, and the
erccuracy of the diaphragm numbers.
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o Optical, glass i,y.;la! form pefore be'i,ngcut into small-slabs for molding. The slabs
may range'in weight from a few oulncesto sezseralpounds.
o Each piece of glass ,is carefully checked on th'is 'instrument ond class'iJtet|us to'index
of refract'ion before be'ing cut for mold'ing.
MANUFACTURINGMETHODS
PopurAR conception has sometimes associatedprecision-madeprod-
"handmade"ucts with methods. However, it has been proved that
modern production methods in many fields provide a quality of
product never before attained, and many examples are seen in our
everyday life. It is now established that lenses and shutters are
products of this type, and the very nature of the processesand the
intricate steps involved in their manufacture can be best carried out
by craftsmen who are specialistsin a particular line. This specializa-
tion of skill is cle arly evident in Kodak lens manufacture. The tech-
nicians and craftsmen who produce Kodak lensesare carefully chosen
and are assigned to work for which they are particularly suited,
either by natural aptitude or by special training.
As pointed out before, the first stage in the creation of a new
photographic lens is its design, which calls for extensive experience
and involves thousands of exact computations. Some points of
interest in lens design have been described briefly on pages 7 -9.
Regular production of a lens for camera use can be started only
after a model of the lens and its mount, 2S conceived by the lens
designer, has been thoroughly tested in the laboratory and under
actual working conditions. For the sake of simplicity and continuity,
a typical lens and its mount will now be traced through the various
stages of production and inspection
T6View original page 16Page 17 · Read text
IENS BIANKS
Oprrcar, glass is examined for possible flaws and the refractive and
dispersive properties are carefully checked. It is then cut or sawed
into squares or slabs of the proper dimensions. These slabs are then
"puddled"heated or in a furnace until the glass is soft. The soft
slabs are then put into a hot mold and pressedinto discs of approxi-
mately the same diameter as the finished lens and with the surfaces
curved, to reduce the time required for grinding. The hot molded
.blanks"discs or are then placed in annealing ovens and allowed to
cool very slowly to remove any internal strains set up in the molding
operation. After being annealed, the blanks are examined and any
which show fire cracks, deep pits, imbedded dirt, large bubbles, or
striations are discarded. The blanks which pass inspection must be
free from these and other defects.
LENSGRINDING
Arrpn being molded and annealed, the blanks are sent to the grind-
itrg rooms. There the blanks are ground by hand with coarse emery
until each surface has approximately the correct curvature and the
proper thickness, with due allowance for the amount of glass that
will be removed by the final grinding and polishing operations.
For the final grinding and polishing, the rough ground blanks are
cemented with pitch to a cast-iron tool in such a way that all their
T7
o Small slabs, cut from the l,orge slabs p'ictured on. the opposite Page, are softened at
r6ooo F. ond then pressed to form the molded,blanks from wh'ich the lenses are ground.
o Electr,ic annealing lve'n wh'ich rernovesany stra'in present'in th.emolded blanks. A
zueek,is regu,iredfor the molded blanks to cool to room temperature.View original page 17Page 18 · Read text
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t:
upper surfaces lie in a single
spherical surface. This is done bY
affixing small buttons of Pitch to
the backs of the blanks, and then
sticking them face down upon a
smooth spherical grinding l.P
having the exact radius of curva-
ture which is to be formed on the
"blockittg lenses. A suitable
body" is then heated and low-
ered onto the pitch buttons. The
pitch softens and sticks to the
hot body, so that when cool, the
whole block of lensescan be liftedo Inspect'i,ng molded and anneo'led lens
btanki f or f ie cracks, striat'ions, a'nd large from the lap and the lenses are
bubbles. ready to grind. The block of
lenses is placed on a revolving spindle, the lens surfaces are painted
with emery and water, and the lap is moved back and forth over the
lenses.The grinding is done with successively finer grades of emery
as the surface becomes smooth and takes on the required curvature.
The lenses are checked carefully with contour gauges and inspected
for scratches as the grinding is continued.
IENS POTISHING
WnBx every lens on the block has been smoothly ground, the emery
is washed away, and the lensesare polished with rouge and water on
a pitch-lined polishitrg shell. Polishing takes from one to ten hours
depettding on the size of the lenses and other factors. The accuracy
of the radius of curvature and the sphericity of the surfaces are
tested by means of a glass test plate of opposite curve. When such a "Newton's test plate is laid upon a lens surface, the presence of
Rings" or interference colors in the thin layer of air between the sur- "frt" faces allows measurement of the closenessof between them to
within a few millionths of an inch.
After being polished, the finished surfaces are sprayed with shellac
"blocking body." They are then remounted, and remove,Cfrom the
polished side down, oo another body, and the second lens surface
'grou*d and polished.
When both sides have been polished, the lens is cleaned by suc-
cessivebathings in alcohol, xylol, ammonium hydroxide, and'soap
.:|, 18View original page 18Page 19 · Read text
suds to remove every trace of grease,shellac,pitch, etc. The lensesare
then inspected again for surface scratches,thickness, and sphericity.
CENTERINGAND EDGING
Arrpn grinding and polishing, the lensesmay be decentered,that is,
the optical and geometrical centers may not coincide and the lenses
must be larger than the mount. To correct these, each lens is
cemented to a hollow lathe chuck in such a way that it is centered to
make the optical axis of the lens coincide accurately with the axis of
rotation of the lathe spindle. This is accomplished by the lathe
operator, who adjusts the lens on the rotating chuck until the image
of a test object, reflected by the lens surface, no longer appears to
rotate. The optical and rotational axes then coincide.
A grinding wheel charged with diamond dust is then brought up
against the edge of the lens, and the excessglassis ground off to make
the lens perfectly symmetrical and of the proper diameter. If the
edge is to be beveled this is also done at this time.
CEMENTING
Ix certain types of lenses,two or more of the elements are cemented
together to form a single unit. Cementing is done in a special room
which is kept scrupulously clean and free from dust. The cement,
Canada balsam, is specially refined to remove dirt and excessturpen-
tine. The elements to be cemented are heated to a predetermined
temperature on automatically controlled hot plates, the Canada
balsam applied, and the two sur-
faces placed in contact at once to o Checking the lens blanhs f or th,ickness.
exclude air bubbles and dust. w'ithThe coarseblanks erneryo.re rough-groundand water to obta,inby handthe
Great care must be taken to keep proper th'ickness ond surface curaoture.
the cemented elements centered,
and after being cemented they
are inspected to make sure that
they did not slip in the operation.
The temperature at which the
cementing is done must be care-
fully controlled so that all sol-
vents will be driven off to insure
a permanent bond without dis-
coloring the balsam which would
turn brown if overheated.
t9View original page 19Page 20 · Read text
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o Rough-ground, blanks cemented to blocksfor grinding an^d?olishing. ^The number of
blanks"OUinea on,a s,ingletool'is deterrn'inedby the shape of the l,enssurface.
MANUFACTUREOF LENS MOUNTS
Mour.rTrr.{c the lens is an important step in the manufacture of a
photographic objective. The quality of a lens depends as much on
the mounting as on the optical parts that comprise it. The mount
for each lens type is designed with the lens. It is of course obvious
that the extreme care which is exercisedin the manufacture of Kodak
lens elements would be wasted if the lens were not properly mounted.
A lens mount must not only center the lens with respect to the
carnera axis and keep the principal planes of the lens parallel with
the camera front, but it must also maintain the separation between
the elements which the designer specifiedin the formula. The mounts
for front-element focusing lenses must be accurately made with the
ippropriate threads. Such mounts must be free from play so that
the lens will be accurately focused for the distance indicated on the
scale, regardless of whether the focusing mount is turned clockwise
or counter-clockwise.
To assure the maintenance of accuracy of mounts, extensive use is
made of special gauges and inspection methods, and particular care
is taken in the selection of the proper material. A complete labora-
tory for testing material is maintained at Rochester. Here, extensive
mechanical and chemical tests are made on the materials used in the
manufacture of mounts and shutters. Samples are tested for
strength, durability, and resistance to corrosion. Special attention
20View original page 20Page 21 · Read text
is paid also to the threads in Kodak mounts. As soon as a thread
chaserstarts to cut threads whose surfacesare not smooth and true to
shape (even though the pitch and count are cbrrect) , it is discarded.
This is only one reason why Kodak mounts have a reputation for
smooth operation, for lack of play, and for remainitrg in accurate
working order. Kodak lens mounts are made by craftsmen and instru-
ment makers equipped with finest tools available for the work.
MOUNTING THE LENS ETEMENTS
WnBx the lens elements have been completed and the mounts made,
the lensesare assembledin the mounts and given a final inspection.
These lenses (with the exception of the simple types of single ele-
ment lenses)are mounted in one of two different ways. One method
is to spin the lens in the mount and the second method makes use
of a retaining ring. Either method makes a positive, permanent job
and keeps the lens in perfect alignment in the mount. Kodak lenses
are never cemented or waxed into place. The mounts for Kodak lenses
are turned so that the lensesare an accurate fit, that is, the lens and
2l
o Lens grind,ing and polishing-Shells charged zt,ith ernery rnove over the rotating
blocks to grind the blanks. For pol'ish'ing, p'itch-l,ined shells are used with rou,ge.View original page 21Page 22 · Read text
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mount diameters are made so
that the lens slips into the mount
snugly and without play. In the
spinning method, the mount is
made with a suitably thin sleeve
on it. After the lens is slipped into
the mount, this sleeve is turned
over with a rounded tool so that
the lens is held firmly in the
mount. The final step in assem-
bly is the mountir,g of the lens in
the shutter.
FINAL INSPECTION
Aprpn the lens has been mounted,
it is sent to the inspection depart-
ment. All the previous inspec-
tions, described before, have been
departmental inspections with
the primary purpose of checking
on the accuracy and the qualityo Centering and edg'ing-Each lens ele-'ment must be centered accurately and 'its of the work being done by that
edge ground to f,t the rnount. particular department. In addi-
tion, final inspection is carried
out in a department entirely independent of the rest of the plant.
The sole purpose of this inspection department is to examine each
lens manufactured to see that it meets the rigid requirements and
specifications to which all Kodak lenses and shutters are made.
Adequate tests are carried out here on each individual lens, not
merely on lensesrepresenting a group.
The great care that is exercisedin the inspection of lensesis exem-
plified by the reproduction on page 26 of a test exposure made with
an Eastman Ektar f16.3,14-inch lens. This is but one of the many
tests to which Kodak lenses are put before they are released for
camera use
Quality in a lens or shutter may not be in evidence upon first
examination. The purchaser must rely to a certain extent upon the
integrity and reputation of the manufacturer to guarantee this
quality. The Eastman Kodak Company confidently accepts that
responsibility.
22View original page 22From the M. Butkus archive. Original publisher and archive notices are retained.
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