Light meters
Weston 650 - Universal Exposure Meter 1936 User manual
User manual for Weston 650 - Universal Exposure Meter 1936. 19 pages in English. Read the original PDF, download or print a copy without registration.
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Document details
- Brand
- Weston
- Model / document
- Weston 650 - Universal Exposure Meter 1936
- Document type
- User manual
- Language
- English
- Pages
- 19
- File size
- 1.9 MB
- Category
- Light meters
- Document date
- Not specified in catalog
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Page 2 · Read text
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i"
WESTON/vtODEL6so
E?-'
UNIVERSAL
PLEASENOTE EXPOSUREMETER *.
A registration card is packed \4rit+;
eachModel 6so ExposureAAeter
when'shipped. Pleasecheck the
serial nurnbershown.on the card
with the nurnberabove the Light
Value scale. This card identifies The"Guide to
you as the owner of your meter. Perfect Exposures
F.14S0 70M 4/37 Prlnted in U.S.A.View original page 2Page 7 · Read text
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THE THEORY OT' EXPOSURE H & D CURVE
The purpose of this chapter is to acquaint When light falls upon a sensitized. Iilm a
the more advariced photographerwith addi- physical change takes place, and this change
tioual methods of obtaining exposure by rvhicll depends upon the intensity and color of the
the scene brightness range can be fitted to the light on the film; upon the time it acts; and
lilm range or latitude so as to obtain auy dc- also upon the sensitivity of the emulsion. When
sired average density in the negative, and the film or plate is developed, the sensitized.
silver salts which were acted upon by lightspecial lighting ellects.
are reduced to metallic silver, and the amount
To obtain these special ellects it may be of reduction is a function of the exposure and
helpful to refer briefly to the theory of expo- the time of development. This elTect was
sure and horv the meter functions with rela- made the subject of scientific investigation by
Hurter & DriIlield. They found that for ation to the H & D exposure curve.
given development, the relation between ex-
It can be shown mathematically that the posure and film density could be expressed by
brightness of an object (the light rellected a curve now known as the H & D curve. A
characteristic curve typical of average com-from it) is the direct criterion of exposure,
mercial films is illustrated on pages 22 and 23.
and not the intensity of light falling upon the This shows the relation between the exposure
object. and the resulting density of the iilm. Thc
lower end which deviates from the straight
Exposure is the product obtained by rnulti- line at the point "d" is the region of under-
plying the light on the photographic film by exposure, the straight portion between .od" and
the time it acts. From this action of exposure "b" is the region of correct exposure and
upon the photographic emulsion it can be the upper portion which extends beyond the
straight line at the point "b,' is the region ofshown that there is a direct relation between overexposure. This does not mean, however,
the brightness of the object to be photographed that the under and over exposur.e regions are
and the resulting effect in the negative. The not frequerrtly useful. Darkest objects and
oxposure meter is therefore calibrated in the brightest high lights of any scene may
brightness units, candles per sq. ft. well extend into the lower and upper regions,
respectively.
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Let us assume a scene consisting of a lime- It is preferable to keep the denslty about
stone building and a few well lighted trees average or below as this gives better printing
with grass in the foreground. The brightest and enlarging properties.
object is the stone r,vork in the sun which, let
us say, has a brightness of 320 candles per SCENES BEYOND THE FILM RANGE
sq. ft. and the darkest object is the trunk of So far we have discussed scenes in which the
a tree rvhich has a brightness of say 25 candles brightest range lies well within the film range,
per sq. ft. l that is, Iess than 128 to 1.
Further, assume we are using a high speed t There are many scenes, however, in which
Orthochromatic film having a speed value of the brightness range greatly exceeds the film 16 to which the dial rvindow is set. Then if {tt range and the photographer, without means
the brightness range, 25-320, is placed at the for determining the facts, wonders rn'hy he
low end of the film range, i.e., with the .oIJ" fails to obtain a pleasing negative. Such
position set to 25 as shown in Fig. 2, and we scenes are, for example, (1) a road in the
use any exposure indicated say 11230 second at rvoods with patches of sunlight on the roacl
f/76, we will obtain a negative having a den- adjacent to deep shadows among the trces
sity variation corresponding to the part of the lvhere the measured brightness may lle 500
film strip from ttMt' to "N," or a negative of candles pei sq. ft. and 1 candle per sq. ft.
lorv average density. rcspectivcly, or (2) a rvaterfall in a rvooded
and rocky area, where the foam may reach alul' Again, if we set the brightness range, 25-820, brightness of 500 candles per sq. ft. and the
midway in the film range as shown in Fig, B shadows on rocks and trees rnay be as low as
and use any exposure indicated, say 1/80 sec- 7, or (3) interiors where portions may be
ond at f/9 we will obtain a negative having lighted by direct sun or skylight and the rest
the densities lying betrveen "P" and ..e,, on in deep shadow.
the film strip, which gives a negative of aver- It is obvious that since ttrese scenes extend
age density. Again, placing the brightncss beyond the lilm range, a theoretically correct
range, 25-320, at the top of the correct film exposure cannot be made and the only re-
range as shown in Fig. 4 by setting the "O:r e, position at 320 and using any exposure in- +- sumed,course ishowever,a compromise.that attemptsIt ruustto photographnot be as-
dicated, say 7/25 second then the at f /5.6,
will have the maximum safe density as shown film { read,ilysuch scenespossibleare todoomedobtain to thefailure.mosi pleasingas it is
in the film strip from "R" to "S" and a slow artistic effects if means are available for ob-
printing {ilm will result. taining accurate data for the exposure. The
reason for this is that the human eye cannot
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adapt itself to appreciate detail simultaneously dress against a dark background, and it is set
in areas of such great dillerences in bright- to the ooO" position, an undesirably great den-
ness. The exposure data cannot be deterrnined sity and halation may result. The latter may
by the eye but are readily furnished by the sometimes produce the desirable artistic effect
Weston Exposure Meter and the actual expo- of brilliance, but where it is undesirable then
sure given depends upon the particular light- it is preferable to place the rvhite object at a
ing effects desired and in this the photographer lorver density on the lilm range. For example,
must exercise his judgUrent and artistic taste. the !'O" position may be set to say 800, placing
For exarnple, take the road in the rvoods. the dress at a lower density and allowing all
If the picture is intended simply as a general objects under 6.5 candles per sq. ft. to be
scene then it is desirable to show detail in the underexposed. One can judge the effect of
trees and allow the sun spots to extend in the these cornpromises by exploring for objects
overexposed regions. The "IJ" position may having a brightness less than 6.5 candles per
be set at 1 candle per sq. ft. which means sq. ft.,-that is, the object brightness indicated
that all objects above 130 candles per sq. ft. by the "U" position.
will be overexposed. This rnay give an un-
pleasant chalky elfect to the high lights in . EFFECT OF COLOR prints and a compromise may be made by set-
fn determining the brightness of objects, ting the "U" position to 2.5, underexposing all
objects having a Iower brightness, and over- sorne consideration must be given to the kind
of film used. Orthochromatic film such as snposing all objects higher than 320 candles
Verichrome and Plenachrome are not sensitive per sq. ft.
to yellow, orange and red, so that for such
On the other hand, if the objcct is to take films, objects of these colors, rvhile possibly
a portrait of a person on the wood's road, for bright to the eye, will be dark to the film.
example a girl in a white dress, then all other This, ho'rvever, is not very troublesome in prac-
parts of the scene must be subordinate to this tice for out-of-door scenes for the reason that
object. In such a case it is preferable to most objects have colors mixed with consid-
measure directly the brightness of the dress erable gray, due to weathering, lvhich reflects and if the "O" position is set to this value, \f enough rvhite light to give a reasonable den-
say 320 candles per sq. ft. one must be con- ' t " sity on the film.
tent with underexposure for all objects lower
than 2.5 candles per sq. ft. ; It is better, however, in measuring the dark-
est and brightest objects in a scene when using
Attention should be called to the fact that these films to select, if possible, objects of a
when the method just described is used where gray or neutral color.
very strong contrast exists such as a white
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It,View original page 13Page 16 · Read text
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negative and meter are suggested for good MISCELLANEOUS
results with various sizes of negatives. INFORMATION
Sizc of Negative Distance Aperture or f/ Numbers
2 Y t x 3 Y + In Contact
3 ! a x 4 l a /a inch F nunrbers are based upon the focal length
5 x 7 2Yz inches of the lens, i.e., the distance between the lens
8 x 1 0 5 inches and the film rvhen the camera is focused for
distant objects. For usiug the exposure meter,
To determine once for all the meaning of the f values as marked on the camera, are
the meter indication in terms of the time re- sufliciently close for all scenes located at a
quired for printing, take any average negative distance exceeding 10 times the focal length
and note the meter indication when the nega- of the lens. For example, when using a lens
tive is placed as described above. Now make of 4 inch focus, the marked f numbers are
a few trial prints for various tirnes and after correct for all scenes at a distance of 40 inches
development determine which time gives the or more from the camera.
best results. Ttris gives the relation between
the meter indication and best printing time For ordinary cameras the effect of distance
for the particular paper tested. 'Ihercafter it upon f numbers need not be considered. But
is only necessary to read the meter and com- for those having cameras with extension bel-
pute the printing time for any negative used. lo'lvs or rvhen tahing close-ups, enlarging, copy-
This same procedure can be carried out for ing, etc", a multiplying factor, as given in the
all types of paper used. A simple method following table, must be applied to the marked
for carrying this out in practice is to compute f number to get the actual f number.
various values and arrange them in tabular
form for easy reference as shown below. Re- ttsta;ce T;ito
rnember that the printing time decreases in Factor i-tTtTTFF.d-l-I: i-1;a
proportion as the light intensity increascs. For example, if the focal length is 4 inches
the inches from lens is 12 carnera and the Sample Table properly distance then the focused, and scene
Meter Indication Time (Seconds) ratio is 72/4 = 3 and the table shows that the
18 72 multiplying factor is 1.5. Therefore an aper-
2 5 8 ture marked say f/8 actually becomes f/12
3 5 0 (f/S x 1.5) and should be used as such in con-
5 0 4 nection with the exposure meter. T'he same
7 0 3 reasoning applies to any other f nurnber. Con'
-30- -31-View original page 16From the M. Butkus archive. Original publisher and archive notices are retained.
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