Gossen MetraWatt Luna-Pro sbc User manual

-
GOSSEN ®
Luna-Pro
sbc
Instruction Manua l
7909-1057YO

This Luna-Pro sbc Instruction Manual is more
than just
an instruction book - it is actually a short
course
in the creative use of an exposure meter.
Section I offers "Basic Operating Instructions".
To
use your Luna-Pro sbc properly you need only read
and follow the simple instructions
in this section.
Section
II, however, moves a step forward -to
"Getting the Most Out Of Your Luna-Pro sbc." Here
you can really find out how to put the unique
versatility of your Luna-Pro sbc to work for you.
Section
III gives you "Helpful Hints" for special
shootings -action, snow and sand, sunsets, night,
and more -the type of information you need for
that extra creativity.
And Section IV provides you with full details
on the
"Accessories" for your Luna-Pro sbc -to turn it into
a true exposure system.
We sincerely hope that this manual will be of help
to you and will answer most of your exposure
measurement questions.
If it does not, feel free to
contact your specialist dealer.
In addition, our Con-
sumer Service Department is available for help
with special requests.
2
Cong ratu lations!
You now own one of the most advanced ex-
posure meter, the heart of the Luna-Pro sbc
System.
The new Luna-Pro sbc System is the most flexible,
versatile and adaptable photographic light measur-
i ng system ever devised, while at the same time
being very simple to use.
In order to get maximum
benefit from the quality design and operating fea-
tures of this precision instrument, please take a few
minutes to
read this instruction manual.
Your new Luna-Pro sbc utilizes the latest advances
in silicon cell sensors and also high performance
electronic circuitry including integrated circuits to
provide fast, accurate, repeatable readings under
the most difficult professional conditions.
The Luna-Pro sbc represents a most significant
development by Gossen GmbH, Erlangen, West
Germany, Europe's largest manufacturer of preci-
sion electrical instruments since 1919, and one of
the outstanding pioneers in exposure meter design
since
1932 .

Table of Contents
Section I. Basic Operating Instructions . 5
I. a. Zeroing the Meter . . . . . . . . 5
I. b. Inserting&Changing the Battery 5
I.c. Setting the Film Speed . 6
I. d. Exposure Factor Scale . 6
I. e. Making a Measurement . 7
I. f. Reading the Scales . . . 7
Section II.
Getting the Most Out Of Your Luna-Pro sbc . 10
II. a. Continuous or Stored Readings . . 10
II. b. The Null Method of Measurement . 11
II. c. Exposure Correction Dial . 12
Il.d. Footcandle Readings
with the Luna-Pro sbc . . .
13
II. e. Carrying Case . . . . . . . 14
11.1. Methods of Measurement . . 14
Il.g. Incident Measurement . . 17
II. h. Reflected Measurement . . 18
II. i. Scene Brightness Range . 19
lI.j. Color Crossover. .21
Il.k. Zone Systems . . . . . . . 21
11.1. Film Reciprocity Failure .... .
Il.m. Intermediate f/stops .. . ... .
Il.n. Intermediate Footcandle Values
and Exposure Time . . . . . . .
Section III. Helpful Hints . . . . . . .
Ill.a. Choosing Between Action Stopping
Ability and Depth-of-Field .
IIl.b. Snow&Sand .
IIl.c. Sunsets .. .
Ill.d. Night Lighting . . .
II I.e. Backlighting .. . .
111.1 . Copying ..... .
Ill.g. Excessive Skylight
Ill.h. Bellows (Extension) Factor
Section IV. Accessories . . . .
Section V. Using Luna-Pro Attachments
Section VI. Appendix . . . .
Service ......... . . .
Specifications . . . . . . . . .
Additional Reference Material
24
24
25
26
26
27
27
28
28
29
29
29
32
37
38
39
40
. 41
3

Operating Parts & Scales
1.
Spherical Diffuser
2.
Green Zero Check Point
3.
Meter Needle
4. Power Switch
5.
Cine Scale
6.
Electronic Flash
Reference Mark
7.
Battery Test Button
12
8.
ASA IndexTriangle
21
9.
Film Speed Scale
10. Exposure Correction Dial
13
11. Computer Dial
14
12. BatteryTest Zone
15
22
13. Exposure Correction Signal
14. ExposureTime Scale
15. Aperture Scale
16
16. Film Speed Setting Disk 17
17.
Exposure Value Scale
18
18. Exposure Factor Scale
19
Index Mark 23
19. Zone System Scale
20. Measuring Cell Window
(under diffuser)
21 . Zero Adjusting Screw
22. Table of Footcandle and '.
Lux Values
23. Battery Compartment Lid

Basic Operating Instructions
The following instructions are a quick operating
guide to the Luna-Pro sbc. For best results, also
read the additional sections describing in more
detail the different functions of the Luna-Pro sbc.
La. Zeroing the Meter
With the battery removed, check to see that the
meter needle
(3) rests on the green zero check point
(2) . If not, turn the zero adjusting screw (21) until
the needle rests on the zero mark.
ca . Lux
mit Diffuso~
bei 18 DIN
'e'
Ie
appr o
I. b. Inserting & Changing the Battery
Your Luna-Pro sbc is supplied with a 9-volt battery
which fits into the battery compartment
at the bot-
tom of the meter. Slide the battery compartment lid
(23) off and attach the battery to the battery clip
inside. Note that the battery can only be connected
one
way. Insert the battery into the battery com-
partment and slide the lid back
on . Check the
battery
by pushing and releasing the power switch
(4) and then pushing in and holding the battery test
switch (7). The meter needle should be well within
the battery test zone
(12) .
5

I.c. Setting the Film Speed
Determine the ASA speed from the data supplied by
the film manufacturer. Rotate the clear film speed
setting disc
(16) by the raised bars until the ASA
speed number
is opposite the white ASA index
triangle (8). A detailed ASA film speed table is on
page 36.
I. d. Exposure Factor Scale
Check to make sure that the exposure factor scale
(10) index mark (18) is at 1. A more detailled expla-
nation of this useful scale is on page 9.
6

I. e. Making a Measurement
Select the method of measurement desired, either
reflected or incident. (For details
on inciden1 vs .
reflected measurements, see section II. f. For
reflected readings slide the spherical diffuser
(1) to
either side of the meter. For incident readings,
slide the sperical diffuser
in front of the measuring
cell window (20) unit it "snaps" into the detent.
Aim the meter at the subject for a reflected light
reading or
at the camera for a incident reading.
Depress
and release the power switch (4 ). Rotate
the computer dial
(11) until the meter needle is over
the "0" null line. Read the desired combination of
f/stops and shutter speeds on the computer scales.
NOTE: When you release the power switch, the
value measured at that moment will be automati-
cally read,
and electronically stored by the Luna-
Pro sbc. To conserve battery life, the meter
switches itself off automatically after 30 seconds,
and your measurement set on the computer dial
remains for convenient
and repeated reference.
For continuous measurements, see page 10.
I. f. Reading the Scales
The Luna-Pro sbc has six scales used to give you
information on ASA index, aperture, shutter speed,
cine speed, exposure value
(EV) , and exposure
factor (EF).
In addition, accessory clip-on scales
are available for direct reading of other light
measuring values such
as footcandles.
7

The time, or shutter speed scale is calibrated from
1/4000 of a second to 8 hours and indicates values
as follows:
Hours are indicated 8h, 4h, etc.
Minutes are indicated 30m,
15m , etc.
Seconds are indicated 30 , 15 , etc.
Fractional seconds are indicated '2, '4, etc.
Note that each section
is alternately colored from
the adjacent sections for ease of reading. The red A/
indicates the proper reading point when using the
electronic flash attachment. See page 34.
The ASA scale is calibrated in standard ASA values
from 0.8 to 100 ,000 (100K). Intermediate values
are shown by short lines. A complete table listing
these intermediate values is on page 38 .
CAUTION: Because of the extreme measuring
range of the Luna-Pro sbc, it
is possible -under
exceptional conditions of very high or low light
levels combined with a very high or low ASA index
-that the computer displays both ends
of the expo-
sure time scale (8h and 1/4000 sec.) When this
occurs, the CORRECT reading
will be the
UPPER part of the scales!
8
EXAMPLES:
ASA 25,000 at HIGHEST LIGHT LEVEL:
Scales.show (above) 1/4000 sec. at
11128
but also (below) 8 hours at f/5.6 etc.
Obviously, HIGH ASA and HIGH light level add up
to SHORT exposure -1/4000 sec. at f/128.
ASA 0.8 at LOWEST LIGHT LEVEL:
Scales show (above) 8 hours
at f/2.8 etc.
but also (below) 1/4000 sec. at f/64
etc.
Obviously LOW ASA and LOW light level add up
to LONG exposure - 8 hours at f/2.8.
The apertu~e or flstop scale is calibrated from fl 128
to f/ O.7. Numerical values are shown on the scale at
full flstop increments. Intermediate values are indi-
cated
by short lines at 1/3 stop increments. A table
of intermediate values and the mathematical for-
mula for calculating f/stops are given in section III.
The zone system scale indicates values from I to
IX.These are the values commonly used in various
zone systems and represent a continuous grey
scale of print values ranging from black to white.
Further explanation
on use of zone system scales
are given in Section II. k. .

The cine scale allows direct reading of apertures
for various cine speeds
(f rames per second).
These speeds correspond
to actual exposure times
on the exposure time scale only for cameras hav-
ing standard shutter angles. For XL cameras or
those with adjustable shutter angles, consult the
camera's instruction book for the equivalent shutter
speeds
and read your exposure opposite that
speed
on the time scale. Also note that some reflex
viewing movie cameras use beam splitters to pro-
vide a light path
to the viewing screen. These beam
splitters reduce the light intensity to the film plane,
so that a correction factor must be applied to the
indicated f/stop. Once determined, the correction
can be programmed into the exposure correction
dial.
An EV (exposure value) scale (17) is provided for
cameras with shutters calibrated
in EV. The Luna-
Pro sbc EV scale is calibrated from -8 to +24.
Numerical values are shown for full EV values with
intermediate values indicated
by short lines at 1/3
EV intervals. Exposure values are used elsewhere
on several scales which will be explained later. It is
important to remember that a change of 1 EV is
equivalent to a change of 1 f/stop.
An EF (exposure factor) scale is included for mak-
ing exposure corrections when using filters, bel-
_ lows, extension tubes, etc.
It is calibrated for expo-
sure factors
up to 64. Detailed information on this
scale is in section II. c.
9

10
Getting the Most
Out of Your Luna-Pro sbc
The preceding condensed instructions gave you
information
on the basic operating procedures for
your Luna-Pro sbc. However, this meter
is extre-
mely versatile, and the following information will
acquaint you with the many creative possibilities
available to you when using your Luna-Pro sbc.
Il.a. Continuous or Stored Readings
The Luna-Pro sbc is capable of either continuously
reading or storing light values. For simplicity of ope-
ration, the
read and hold method is used. For eva-
luation of different lighting levels such as when
using zone systems, the continuous method
is
used. Both methods are activated by the same
power switch.
To operate the meter in the read and hold mode,
the power switch
ON /OFF button index mark (a)
must be aligned with the square switch position
indicator
(b). Simply depress and release the
power switch. The meter will automatically read
and electronically hold the value of the light level
present at the moment when the button was relea-
sad. Because advanced electronic circuitry
and a
silicon blue cell are used in the Luna-Pro sbc, the
measurement
is instantaneous with no memory or
lag. This reading will be stored and available for a
period of
30 seconds after the button is released.
After the one minute period,the meter automatically
turns itself off, prolonging battery life. Additional
readings can be taken at any time by repeating the
above sequence.
To operate the meter in the continuous mode, sim-
ply depress and hold the ON /OFF button in. The
meter will now respond
to all changes in light
values. For long term measurements, the
ON /OFF

switch has a lock position which is indicated by the
round switch position indicator
(c). To activate and
lock the meter on:
1) Depress and hold the power switch in.
2) Rotate the switch button clockwise until the
index mark
is aligned opposite the round switch
position indicator.
The meter will now remain
on for constant readings
until the switch button is rotated counterclockwise
opposite the square position indicator where the
read and hold mode will go into operation for one
minute, after which the meter will again turn itself
off.
NOTE: Be sure to return the switch button to the
read
and hold position (square mark) after using.
Failure to do so will result in short battery life.
II.
b. The Null Method of Measurement
Laboratory instruments have long used the null
method of measurement for obtaining precise rea-
dings. This method has been incorporated into
your Luna-Pro sbc for maximum accuracy and
ease of reading.
The basic operating difference between the Luna-
Pro sbc and a conventional meter is that, instead of
using various points along a complete scale length,
only one position (the null point)
is used for all rea-
dings and at all light levels. This results
in greater
accuracy and ease of operation. There
is no need
to change scale ranges or
to read different scales.
When the needle is set at the null point, the compu-
ter instantly shows a complete read-out of the mea-
surement.
To expand the capabilities of the Luna-Pro sbc
further, its meter face
is also calibrated in 1/3 EV
increments from the null position to ± 3 EV for use
in scene brightness measurements and zone
system applications. Additional information
on this
extremely useful feature will be found in section II. i.
If the meter needle is placed in the "over" or
"under" range, the readings on the calculator dial
will result
in over or underexposure by the value
indicated, compared to a standard exposure.
Each numerically indicated major division
on the
meter face equals one
EV (a change of one EV
equals a change by one flstop or one shutter speed
setting); the small intermediate dots are equal to
1/3 EV.
11

II. c. Exposure Correction Dial
Occasionally, the indicated exposure readings
obtained with any light meter must
be modified for
best results. This
is especially true when using fil-
ters or when taking close-up pictures where the
longer lens to film distance results in reduced light
at the film plane. To correct for these effects, com-
monly called filter factor and bellows
(e xtension)
factor, additional exposure must be given to the
film. In addition, you may, for various creative
reasons, wish to depart from the standard expo-
sure values. For these situations, the Luna-Pro
sbc, with its exposure correction dial, is ideal.
Normally when making exposure corrections, the
correction factor must be calculated and applied
each time a reading is taken. However, with the
Luna-Pro sbc, the exposure change can be prog-
rammed into the exposure correction dial. Any
readings then will automatically be corrected
as
taken.
The exposure correction dial
is calibrated to work
both
in EV (e xposure value) and EF (e xposure fac-
tor). Two index marks are provided at the center or
normal positions for each correction method. In
addition, the red exposure correction signal gives a
12
visual indication any time the exposure correction
dial is in use.
:fo use the exposure correction feature, determine
the correction factor desired,
in either EV or EF,
and rotate the exposure correction dial while hold-
ing the computer ring stationary until the white
index mark
is opposite the correction value. Any
readings now taken will reflect this correction.
For example, assume that a filter with a filter factor
of 4 x
is being used which represents a change of
2 stops. By moving the index mark of the
EF ring to
a position opposite the number 4, the meter read-
ings will automatically be compensated for the 2
stop difference.

Rotating the exposure correction dial corrects the
indicated exposure by changing the shutter speed
(and flash symbol), cine speed, and EV scales.
Therefore, this feature can be used for still photo-
graphy using available light and artificial ligth
including flash, motion picture photography, and
wi
th cameras calibrated only in EV.
After completing "corrected" measurements, be
sure
to return the correction dial to its "0" posi-
tion (red signal will be covered by\black tab).
ILd. Footcandle Readings
With The Luna-Pro
sbc
The Luna-Pro sbc is a precision instrument
designed to give highly accurate photometric read-
ings specified in readily usable photographic terms.
However, footcandle readings can also be obtained
with the Luna-Pro sbc, either by converting the
photographic reading or
by use of an accessory
snap-on footcandle scale.
A conversion table of EV to footcandle readings is
included on the underside of the meter.
To deter-
mine the equivalent footcandle reading, set the
ASA film speed scale to 50, slide the spherical dif-
fuser over the cell window for incident readings,
point the meter toward the light source and take
an
EV reading (null the meter). Turn the meter over
and read the footcandle value opposite the EV
reading just obtained. Similarly, lux values can also
be determined. Note that for each change of one
EV, the footcandle level changes by a factor of 2.
This is because the EV scale is equivalent to a full
stop scale in that each change of one EV or one
f/stop results
in either twice or half the amount of
light. A formula suitable for calculating intermediate
values of footcandles is given in section III along
with pre-calculated values at 1/3 EV increments.
For direct reading of footcandles,
an accessory
snap-on footcandle scale is supplied with the
Studio Attachment. When attached, this scale
allows quick, direct read-out of
t~e equivalent foot-
candle readings without having
to change ASA
values or using a conversion table. Detailed
instructions for its use are included with the scale.
The most precise footcandle readings are obtained
by means of a flat diffuser such as the one supplied
with the Studio Attachment. When using the spher-
ical diffuser of the Luna-Pro sbc, all the light falling
on the diffuser from an angle of approximately 1800
is integrated for a final reading. Since most photo-
13

111
II
graphic subjects are three dimensional, this results
in more accurate photographic exposures, but can
give improper footcandle readings.
When using the spherical diffuser, footcandle read-
ings are most accurate when reading direct light
beams such as from spots, are lights, etc.
II. e. Carrying Case
Your Luna-Pro sbc is supplied with an exceptionally
practical carrying case.
It is made of smooth, sturdy
materials for long life and extra protection for the
meter. The handy design
and a double zipper, as
well as the belt loop ma ke this case suitable for pro-
fessional use.
14
II. f. Methods of Measurement
There are two basic methods of obtaining measure-
ments wit
J:1 the Luna-Pro sbc, incident and reflected
light readings. Both methods
are popular and when
used properly, both
are vaiid and will give good
results. However, to evaluate properly the ways in
which these two methods function, it is necessary to
discuss briefly how the meter operates and how film
responds to light. It is beyond the scope of this man-
ual to get into a detailed discussion of sensitometry,
the study of tone reproduction. There are many
excellent books available on the subject, some of
which
are listed in the appendix. This manual will
just relate in simple terms, how the Luna-Pro sbc
works
and under which conditions you may wish to
use either incident or reflected light readings.
All films have characteristic responses to light
which, although they may vary from film to film and
with changes
in storage and processing, are rela-
tively predictable. This consistency of response
is
what allows the use of light meters and other photo-
graphic instruments
to predict the final outcome of
an exposure.

Film responds to only a limited range of illumination
le ve ls before its ability to .record that light illumina-
tion level properly is lost. Any instrument designed_
to measure or expose film must take that into con-
sideration. The response of
the film to light is gener-
ally graphically illustrated by what is called a
"characteristic curve" or H&D curve, named for
Hurter and Driffield who originated its use. Although
it is not necessary to use such a curve to determine
exposures, using one
as an illustration will help in
evaluating proper light measuring techniques. A rep-
resentative sample H& D curve for a film is illus-
trated below.
2.00
1.60
~ 1.20
in
z
~ .80
Should::..,, __ _
Straight Li ne
Toe
. 401---_-
0.30 0.60 0.90 1 .20 1.50 1.80 2. 10 2.40
RELATIVE LOG E
This curve shows, among other things, the change
of density of the film
vs. the log of the exposure.
With negative film,
as the exposure increases, the
negative density increases. It
is broken down into
three distinct regions, the toe, straight line portion,
and shoulder. In order to record detail properly on
film, the light values (long exposure) should fall
within the range where they intersect the straight
line portion of the curve. If the exposure falls into the
area of the toe or shoulder, the film will lose shadow
or highlight detail respectively. This
is because, once
those areas
are reached, little or no change in film
density occurs with a change in exposure, and it is
the change of density that produces differentiation
and detail. Therefore, your light meter must give you
an exposure value that will adjust the measured light
so that when it reaches the film, it will fall within the
straight line portion of the film's recording ability.
The H&D curve shown above indicates relative log
exposure. However, because different films have dif-
ferent light sensitivity ranges which would affect the
density vs.
log exposure in actual use, the meter
must
be programmed for these differences. The
ASA film speed setting control on the calculator dial
of the meter accomplishes this programming.
15

In order for this ASA value to be meaningful, all
meters and other light measuring devices that
relate to photographic applications must take into
account not only the film speed, but also the reflec-
tivity of the object being photographed. This is
because the film does not know what the reflectiv-
ity of a particular object is. It only responds to light
levels. Therefore,
all other conditions being equal,
a light subject with a low level of illumination may
record
on film the same as a dark object with a high
level of illumination. To standardize these varying
conditions
and to allow you to work with different
meters and films, a reflectance of 18% value and
the understanding that it represents a "typical aver-
age" is the basis for readings taken with both
reflected and incident methods of measurement,
although under the same lighting conditions, differ-
ent readings for the same scene can be obtained
when using both methods, depending
on subject
reflectivity. This may seem strange at first, but it is
true, and sometimes causes confusion. To elimi-
nate this confusion (something no meter or other
device can do), you must consider your subject
matter and how you want it to appear
on the film.
For simplicity, the discussion of this evaluation
16
method will be broken down into a discussion of
incident and reflected light measurements.

II. g. Incident Measurement
When reading incident light, the spherical diffuser
is placed in front of the measuring cell window ami
pointed toward the camera, i. e. opposite the sub-
ject being photographed, so that the diffuser will
receive the same light intensity and distribution as
that falling on the subject. The reading at this point
indicates the strength of the light, but does not indi-
cate the light value reflected from the subject into
the camera lens and onto the film.
It does indicate
the light value that would
be reflected into the lens
from an 18% average reflective subject. Therefore,
when working with subjects that are primarily very
light or very dark, the incident exposure reading
rndicated should be adjusted to compensate for the
difference
in reflectivity from the 18 % standard.
When the subject
is very light, decrease the expo-
sure by 1/2 to 1 f/stop. When the subject is very
dark, increase the exposure
by 1/2 to 1 stop. The
amount of change
to the exposure will depend on
your judgement as to the degree of variation in sub-
ject reflectivity from an average scene.
Situations may arise where you have extremes of
light and dark subjects, all of which are important in
the same scene. Under these conditions, the meter
, /,"" I
/ I
... ..-/'" I
I
I
I
I
should be used in the reflected light method as
described under scene brightness range and zone
systems.
Incident light readings are most valuable when
determining exposures where the subject
is inac-
cessible
and receives the same illumination as the
meter. They also allow your
to determine the indi-
vidual strenghts of multiple light sources striking
one subject
by reading each source independently.
In most cases with average subject matter, the inci-
dent method is a fast, simple and accurate way to
determine exposure.
17

II. h. Reflected Measurement
When reading reflected light, the meter is pointed
toward the subject and light reflected from the sub-
ject passes through a collecting lens onto the
measuring cell. This is the same type of path the
light takes when exposing film in your camera. The
meter cannot "read" any single element
in its field,
such as a face or highlight; it integrates all the light
reflected throughout the measuring field, and
indicates an exposure which will record the total
picture on the basis of an overall 18 % value.
In most cases, you can simply use this reading to
get a perfectly exposed picture. However, there are
a few situations where the readings should
be
modified.
The Luna-Pro sbc has a measuring angle of 300
when taking a reflected reading. The light from all
objects within that 300 measuring range will be
averaged to give you the final reading. If you have
one or more objects that are significantly lighter or
darker than the rest of the scene, the objects will
bias the reading away from the average. In cases
such
as this, the meter should be moved in closer
to the main subjects of interest or one of the acces-
sory spot attachments used to eliminate the effect
18
of the light or dark areas. As an alternative, an inci-
dent reading can
be taken.
When measuring a subject that departs signific-
ar.t1y from an 18 % reflective surface, you may wish
to modify your readings. This is because the read-
ing indicated will make the subject appear
on the
film as if it were 18 % reflective.
In certain cases, you may not want the subject
being measured to fall into that category. For exam-
ple, if the indicated reading is set in your camera
when measuring a brilliant white bridal gown, the
resulting image of the gown on the film will appear
with the same density
as if it were 18 % gray
instead of white. Here again, you may wish
to use

an incident reading or compensate the reflected
reading by increasing exposure. The same is true
for very dark objects,
i. e., a black tuxedo, except
the exposure would be decreased.
Reflected readings are particularly useful when try-
ing to evaluate the relative range of reflected light
from various subjects that may have different reflec-
tivity and may
be receiving different amounts of
light. Because the reflected reading measures the
light reaching the lens, differences in reflectivity
and level of illumination are accounted for. There-
fore, your can determine the extremes and distribu-
ti
on of light from the scene just the way your film
will record
it. This technique is covered in sections
Scene Brightness Range and Zone Systems.
II. i. Scene Brightness Range
In order to assure proper exposures for highlight
and shadow detail in scenes with a wide range of
light intensity and subject reflectivity, the extent of
the lighting range must
be determined. The Luna-
Pro sbc is ideally suited for this type of measure-
ment because of its null meter design.
To utilize this function, you must first determine, by
testing the limits of exposure change for highlight
Proper me te ring aids in r ecordi ng all detail of a scene.
and shadow areas from average that are accept-
able to you with your film. Once this is done, the
calibrated reference scale on the meter will
automatically indicate if you are within acceptable
limits of the film.
For example, if your testing with a particular type of
film shows that you could accept an exposure
UNDER
OVER
19

change from average of UNDER (under exposure)
2 to OVER (over exposure) 21 /2 EV , your total range
would be 4 1/2 EV. Using reflected measurement,
you could then
read the light from the most impor-
tant area of the scene
and then null for that read-
ing. Then, without further adjustment of the cal-
culator dial, you could take light readings from high-
light and shadow areas and read the EV variance
of these areas.
If, in this case, the readings fall
within the UNDER 2 to OVER 21 /2 EV range, your
exposures will be good. However if for example,
your readings resulted in UNDER 3 and OVER 1,
you would lose shadow detail, even though the
total range is still only 4 EV. A simple solution would
then be to reread the shadow intensity and rotate
the computer dial until the meter needle
is opposite
2
on the UNDER side which is within the film limits.
UNOE .R
OVER
20
Then recheck the highlights which should now read
OVER 2. You would then use the new exposure
setting indicated
on the computer dial. The scene
brightness range has not changed, but the meter
has adjusted to your exposure
so that your are
working within the range of the film.
To see this
graphically in terms of film response see the H&D
curves to the right.
It is important to note that this exposure adjustment
method works best when using negative films
because different density levels can be adjusted for
in printing. With transparency films, this type of
exposure adjustment should
be used very carefully
because you are viewing the original without the
benefit of printing correction.