Light Meter - Posted 2-17-'03

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This Luna-Pro F 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 F 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 F". Here you can really find out how to put the unique versatility of your Luna-Pro F 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 F--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 BMC specialist dealer. In addition, our Consumer Service Department is available for help with special requests.


The Luna-Pro F is the only combination flash and daylight meter with null meter readout--the only system that gives you all the critical information you need for perfect pictures faster and more accurately than any other exposure meter.4www.butkus.org

The Luna-Pro F is a very flexible, versatile and adaptable photographic light metering system, while at the same time being very simple to use. In order to get maximum benefit from the state of the art design of this precision instrument, please take a few minutes to read this instruction manual.

Your new Luna-Pro F utilizes the latest advances in silicon blue 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 F is the result of significant research and development by Gossen GmbH, Erlanger, West Germany, Europe's largest manufacturer of precision 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. Type of Reading 7

I.f. Mode of Measurement 7

I.g. Taking a Measurement 7

I.h. Reading the Scales 8

Section II. Getting the Most Out of Your Luna Pro  11

II.a. Continuous or Stored Readings 11

II.b. The Null Method of Measurement 12

II.c. Exposure Correction Dial 13

II.d. Footcandle Readings 14

II.e. Carrying Case 15

II.f. Methods of Measurement 15

II.g. Incident Measurement 17

II.h. Reflected Measurement 18

II.i. Scene Brightness Range 20

II.j. Lighting Ratios 22

II.k. Fill Flash 22

II.l. Multiple Flash 23

II.m. Shutter Speeds and Flash Measurement 23

II.n. Color Crossover 26

II.o. Zone Systems 27

II.p. Film Reciprocity Failure 28

II.q. Intermediate F Stops 29

II.r. Intermediate Footcandle Values and Exposure Time 29

Section III.  Helpful Hints a.... 30

III.a. Choosing Between Action Stopping Ability and Depth-of-Field 30

III.b. Snow & Sand ............ 31

III.c. Sunsets 31

III.d. Night Lighting 32

III.e. Backlighting 32

IlI.f. Copying 33

III.g. Excessive Skylight 33

III.h. Bellows (Extension) Factor 34

Section IV. Accessories 37
Section V. Appendix 40
Service 41
Specifications 42
Additional Reference Material 43

Operating Parts & Scales

1. Spherical Diffuser

2. Green Zero Check Point

3. Meter Needle

4. Power Switch

5. Electronic Flash Reference Mark

6. Cine Scale

7. Mode Selector

8. ASA Index Triangle

9. Film Speed Scale

10. Exposure Correction Dial

11. Computer Dial

12. Battery Test Zone

13. Flash Range Indicator

14. Exposure Time Scale

15. Aperture Scale

16. Battery Test Button

17. Exposure Correction Signal

18. Film Speed Setting Disk

19. Exposure Value Scale

20. Zone System Scale4www.butkus.org

21. Exposure Factor Scale Index Mark

22. Measuring Cell Window (under diffuser)

23. Zero Adjusting Screw
24 Table of Foot candle and Lux Values

25. Battery Compartment Lid


Basic Operating Instructions

The following instructions are a quick operating guide to the Luna-Pro F. For best results, also read the additional sections describing in detail the different functions and applications of the Luna-Pro F.

1. a. 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 (23) until the needle rests on the zero mark.

1. b. Inserting & Changing the Battery

Your Luna-Pro F is supplied with a 9-volt battery which fits into the battery compartment at the bottom of the meter. Slide the battery compartment lid (25) 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 compartment 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 button (16). The meter needle should be well within the battery test zone (12).4www.butkus.org

1. c. Setting the Film Speed
Determine the ASA speed from the data supplied by the film manufacturer. Rotate the clear film speed setting disc (18) 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 40.

1. d. Exposure Factor Scale
Check to make sure that the exposure factor scale index mark (21) is at 1. A more detailed explanation of this useful scale is on page 10..

1. e. Type of Reading
Select the method of measurement desired, either reflected or incident. (For details on incident vs. reflected measurements, see section 11. f.). For reflected readings slide the spherical diffuser (1) to

1. f. Mode of Measurement

Select the mode of measurement desired, either flash or daylight (ambient light). For daylight measurement, the red mode selector (7) should be in the depressed position; for flash measurement the mode selector should be in the raised position. Depress and release the mode selector to change the mode of measurement (i.e., from flash to ambient). There is a graphic illustration on the side of the meter which shows the positioning of the mode selector necessary to take f lash or ambient readings.

Note: The flash mode can be used for taking incident or reflected readings.

1. 9. Taking a Measurement

Follow Basic Operating Instructions steps 1. a. thru I. f.

For daylight measurement, mode selector (7) should be in the depressed position (see Section I. f.). Aim the meter at the subject for a reflected light reading or at the camera for an 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/stop and shutter speed on the computer scales.

For flash measurement, mode selector (7) should be in the raised position (see Section I. f.). Aim the meter as indicated above. Depress and release the power switch (4). Fire the flash. Rotate the computer dial until the meter nulls. It is important to note that the red zero mark on the exposure correction dial should remain between the two red triangles on the meter face when pulling. If the zero mark goes beyond either of the red triangles, the flash intensity is beyond the range of the meter. When past the right triangle the light level is too low. When past the left triangle, the light level is too high.

Read the proper f/stop opposite the red flash indicator on the computer dial. This indicator is located between the 1 and 2 second exposure marks.

NOTE: When you release the power switch, the value measured at that moment will be automatically read, and electronically stored by the Luna-Pro F. 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 Section II. a.

1. h. Reading the Scales

The Luna-Pro F has seven scales to give you information on ASA, aperture shutter speed, cine speed, exposure value (EV), exposure factor (EF) and Zone System values.

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 11 indicates the proper reading point when using the flash measurement mode.

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 in on page 40.4www.butkus.org

CAUTION: Because of the extreme measuring range of the Luna-Pro F it is possible--under exceptional conditions of very high light levels combined with a very high ASA index--that the computer displays both ends of the exposure time scale (8h and 1/4000 sec.). When this occurs, the CORRECT reading will be the UPPER part of the scales!



Scales show above       1/4000 sec. at f/128 
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.

The aperture or f/stop scale is calibrated from f/128 to f/0.7. Numerical values are shown on the scale at full f/stop increments. Intermediate values are indicated by short lines at 1/3 stop increments. A table of intermediate values and the mathematical formula for calculating f/stops are given in Section III.

The cine scale allows direct reading of apertures for various cine speeds (frames per second). These speeds correspond to actual exposure times on the exposure time scale only for cameras having 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 provide 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 (19) is provided for cameras with shutters calibrated in EV. The LunaPro F 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 I important to remember that a change of 1 EV is I equivalent to a change of 1 f/stop.

An EF (exposure factor) scale is included for making exposure corrections when using filters, bellows, extension tubes, etc. It is calibrated for exposure factors up to 64. Detailed information on this scale is in Section II. c. The zone system scale provides you with the capacity to read lighting ranges (in zone system values I thru IX) directly from the computer dial of the meter. Further information on zone systems can be found in Section II. k.


Getting the Most Out of Your Luna-Pro F

The preceding condensed instructions gave you information on the basic operating procedures for your Luna-Pro F. However, this meter is extremely versatile, and the following information will acquaint you with the many creative possibilities available to you when using your Luna-Pro F.

11. a. Continuous or Stored Readings

The Luna-Pro F is capable of either continuously reading or storing light values. For simplicity of operation, the read and hold method is used. The continuous method of measurement can be used for the evaluation of different lighting levels (such as when using zone systems) as well as the measurement of commutative flash.

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 released. Because advanced electronic circuitry and a silicon blue cell are used in the Luna-Pro F. the measurement is instantaneous with no memory or lag. The reading will be stored and available for a period of thirty seconds after the button is released. After this period, the meter automatically turns itself off, prolonging battery life. Additional readings can be taken at any time by repeating the above sequence.4www.butkus.org
To operate the meter in the continuous mode, simply 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 readings. This method has been incorporated into your Luna-Pro F for maximum accuracy and ease of reading.

The basic operating difference between the LunaPro F 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 readings 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 computer instantly shows a complete read-out of the measurement.

To expand the capabilities of the Luna-Pro F 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, zone system applications and lighting ratio measurements. Additional information on this extremely useful feature will be found in Section II. i.

If the meter needle is placed in "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 f/stop or one shutter speed setting); the small intermediate dots are equal to 1/3 EV.

11. 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 filters 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, commonly called filter factor and bellows (extension) factor, additional exposure must be given to the film. In addition, you may, for various creative reasons, wish to depart from the standard exposure values. For these situations, the Luna-Pro F 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 F the exposure change can be programmed into the exposure correction dial. Any readings will then be automatically corrected.

The exposure correction dial is calibrated to work both in EV (exposure value) and EF (exposure factor). Two index marks are provided at the center or normal positions for each correction method. In addition, the red exposure correction signal (17) gives a visual indication any time the exposure correction dial is in use.

To use the exposure correction feature, determine the correction factor desired, in either EV or EF, and rotate the exposure correction dial while holding the computer ring stationary until the white index mark is opposite the correction value desired. Any readings now taken will reflect this correction.

For example, assume that a filter with a filter factor of 4x is being used. This represents a change of 2 stops. By moving the index mark of the EF ring to a position opposite the number 4, the meter readings 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 photography using available light and artificial light including flash, motion picture photography, and with cameras calibrated only in EV.

After completing "corrected" measurements, be sure to return the correction dial to its "O" position (red signal will be covered by black tab).

11. d. Footcandle Readings With The Luna-Pro F

The Luna-Pro F is a precision instrument designed to give highly accurate photometric readings specified in readily usable photographic terms. However, footcandle readings can also be obtained with the Luna-Pro F either by converting the photographic reading or by use of an accessory snap-on foot candle scale.

A conversion table of EV to foot candle readings is included on the underside of the meter. To determine the equivalent foot candle reading, set the ASA film speed scale to 50, slide the spherical diffuser 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 foot candle value opposite the EV reading just obtained. Similarly, lux values can also be determined. Note that for each change of one EV, the foot candle 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 foot candles is given in Section III along with pre-calculated values at 1/3 EV.

The most precise foot candle readings are obtained by means of a flat diffuser. When using the spherical diffuser of the Luna-Pro F. all the light falling on the diffuser from an angle of approximately 180° is integrated for a final reading.

 Since most photographic subjects are three dimensional, this results in more accurate photographic exposures, but can give improper foot candle readings.

When using the spherical diffuser, footcandle readings are most accurate when reading direct light beams such as from spots, arc lights, etc.

11. e. Carrying Case
Your Luna-Pro F is supplied with an exceptionally strong and functional carrying case. It is constructed of the finest heavy-duty materials for long life and extra protection for the meter. Extra thick material and heavy stitching make this case suitable for the abuse encountered in professional usage. The complete top section of the case is removable for ease of handling when taking frequent exposure readings.4www.butkus.org

To insert the meter, open the case by unsnapping the fastener at the rear of the case and swing the top section forward. Insert the meter strap through the openings at the rear of the case. Place the meter into the bottom section of the case and secure with the retaining strap. To remove the top section of the case completely, unsnap the fastener at the bottom of the case.

11. f. Methods of Measurement

There are two basic methods of obtaining measurements with the Luna-Pro F. incident and reflected light readings. Both methods are popular and when used properly, both are valid 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 manual 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 F 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 relatively predictable. This consistency of response is what allows the use of light meters and other photographic instruments to predict the final outcome of an exposure.

Film responds to only a limited range of illumination levels before its ability to record that light illumination level properly is lost. Any instrument designed to measure or expose film must take that into consideration. The response of the film to light is generally 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 representative sample H & D curve for a film is illustrated below.


This curve shows, among other things, the change of density of the film vs. the "zog" (yes, correct spelling from manual) 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 (log 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 different 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.

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 reflectivity of the object being photographed. This is because the film does not know what the reflectivity 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 average" is the basis for readings taken with both reflected and incident methods of measurement. However, under the same lighting conditions, different 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 eliminate 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 method will be broken down into a discussion of incident and reflected light measurements.

11. 9. Incident Measurement

When reading incident light, the spherical diffuser is placed in front of the measuring cell window and pointed toward the camera, i.e. opposite the subject 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 indicate the light value reflected from the subject into the camera lens and onto the film. It does not 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 indicated should be adjusted to compensate for the difference in reflectivity from the 18% standard. When the subject is very light decrease the exposure 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 judgment as to the degree of variation in subject reflectivity from an average scene (18% reflectivity).

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 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 inaccessible and receives the same illumination as the meter. They also allow you to determine the individual strengths of multiple light sources striking one subject by reading each source independently. In most cases with average subject matter, the incident method is a fast, simple and accurate way to determine exposure.

11. h. Reflected Measurement

When reading reflected light the meter is pointed toward the subject from the camera position without the spherical diffuser (1) over the measuring cell. Light reflected from the subject 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 F has a measuring angle of 30° when taking a reflected reading. The light from all objects within that 30° 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 accessory spot attachments used to eliminate the effect of the light or dark areas. As an alternative, an incident reading can be taken.

When measuring a subject that departs significantly from an 18% reflective surface, you may wish to modify your readings. This is because the reading 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 example, if a reflected 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 trying to evaluate the relative range of reflected light from various subjects that may have different reflectivity and may be receiving different amounts of light. Because the reflected reading measures the light reaching the lens, differences in subject reflectivity and level of illumination are accounted for. Therefore, you can determine the extremes and distribution 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.