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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 LunaPro F is ideally suited to this type of measurement because of its null meter design.

To utilize this function, you must first determine by testing the limits of exposure change for highlight and shadow areas from average that are acceptable to you with your film. Once this is done, the calibrated reference scales on the meter will automatically indicate if you are within acceptable limits of the film.4www.butkus.org

For example, if your testing with a particular type of film shows that you could accept an exposure change from average of UNDER (under exposure) 2 to OVER (over exposure) 2 1/2 EV, your total range would be 4 1/2 EV. Using reflected measurement, you could then read the light from the most important area of the scene and then null for that reading. 

Then, without further adjustment of the calculator dial, you could take light readings from highlight and shadow areas and read the EV variance of these areas. If, in this case, the readings fall within the UNDER 2 to OVER 2 1/2 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.

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 you 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.4www.butkus.org 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.

With transparencies, about 1 EV is the largest practical shift if your main subject is close to 18% reflectance.

Situations may arise where the meter shows a range of light intensity that is beyond the total range of film acceptance. In these cases, the use of fill light to lighten shadows or a "gobo" (a device to block or modify light such as a dark card) to soften highlights may be indicated. When the proper corrective action is taken, the scene brightness range can again be checked to be sure the limits of the film are not exceeded. Modifying the lighting can also be used instead of shifting the exposure as mentioned above if so desired, as in the case of transparency film where the main subject is close to 18% reflectance such as with some skin tones.4www.butkus.org

11. j. Lighting Ratios

Lighting ratios, the relative strengths of different lights in a scene, can be used to create certain moods or effects. Sometimes, manipulation of lighting ratios is needed to hold detail in shadow and highlight areas.

To determine a lighting ratio, take an incident reading of the main light and null the meter. Then, without readjusting the computer dial, read the other light or lights in the scene. When reading the secondary lights, deflection of the meter needle will indicate the strengths of those lights in relation to the main light. The method of reading lighting ratios is similar to that described under Scene Brightness Range.

11. k. Fill Flash

When lighting ratios are very high, the difference of the light levels in the areas of direct light and shadow may be so great that the film will not be able to record detail in both areas at the same time. If this occurs, a useful technique for bringing lighting ratios to a more manageable level is fill flash.

By using supplemental flash, generally electronic flash, a sufficient level of light can be introduced into the shadow areas to make proper recording of detail possible. The Luna-Pro F is a useful tool in determining the relative strengths of available light and flash illuminating the scene and can help to adjust to the proper lighting ratios.

Example Method I:

Assume you are shooting a scene where, in order to hold detail in a shadow area, you want the shadow exposure to be 2 stops under the mid-tone reading.

1) Take an incident reading and null the meter.
2). Without moving the computer dial, read. in the shadow area. The needle deflection indicates the shadow is 3 stops under your mid-tone (incident) reading. If you wish, electronic flash can be used to bring more light into the shadow area and bring the shadow illumination into the desired range.
3) Select your working aperture and shutter speed from the initial incident reading (i.e., at 1/125th second).
4) Since you wand the shadow area to be 2 stops under the mid-tone, set the flash mark (5) at f5.6 (2 stops under f11).
5) Take a reading (with the Luna-Pro F in the flash mode) with the flash unit directed toward the shadow area.
6) Manipulate the flash unit (changing the position or power control) until the meter needle deflects to the null point. Make sure that little, if any, ambient light strikes the measuring cell of the meter.

If you have a leaf shutter camera and are not able to adjust the flash, you card determine fill flash exposure by adjusting the. aperture and shutter speed settings.4www.butkus.org4www.butkus.org


Example Method II:

Follow steps 1 to 3 as indicated for Method I.

4) Fire the flash into the shadow area and take a reading with the Luna-Pro F in the flash mode. Let us assume that the flash is not powerful enough to bring the exposure into the two stop range and the Luna-Pro F indicates an exposure at f4.

5) Change your initial exposure to 1/250th second at f8. Note that this will give you the same exposure value as 1/125th second at f11.

6) The flash reading of f4 is now within the desired two stop range of the mid-tone reading at f8.

When doing any work with flash, you must work within the camera's 'sync' speed (the shutter speed at which the flash will synchronize with the shutter).

II. I. Multiple Flash

Occasionally the light output from a singular flash may not be sufficient to enable you to work at the f/stop desired. When this happens, multiple flashes may resolve the problem. The Luna-Pro F can assist you in measuring the cumulative exposure of multiple flash.

Example:

The indicated f/stop, after your initial flash measurement is full; you wish to work at f22. Adjust the computer dial until the red flash reference (5) lines up with f22. With your Luna-Pro F in the flash mode, reset the meter and leave the power switch in the continuous read position. Repeatedly fire the flash. Count the number of flash needed to null the meter (bring the meter needle to the zero point).

It is important to note that for each f/stop increase desired you must double the number of flashes. Therefore, if your desired f/stop is more than a few stops away from the indicated f/stop, this method becomes impractical.

II. m. Shutter Speeds and Flash Measurement
Most electronic flash units have a relatively short duration. Therefore, actual film exposure by the flash is not affected by changes in camera shutter speed as long as synchronization is maintained. However, changes in shutter speeds will alter the effect of ambient light on the overall exposure. (As the shutter speed changes, the portion of the total exposure caused by the flash remains constant, but the portion caused by the ambient light will vary.) As long as the flash output is considerably higher than the ambient, this effect can be ignored. But when the level of ambient light exposure approaches that of the flash, attention must be given to the effect of shutter speeds. The circuitry of your Luna-Pro F is designed to indicate the f/stop which will produce correct overall exposure with a shutter speed of 1/100th to 1/125th second. If the ambient light is extremely bright, and a different shutter speed is used, the indicated f/stop may have to be modified to compensate for variations in ambient exposure caused by the change in shutter speed. To determine if compensation is required, two parallel measurements must be taken from the same position:

1. Normal measurement (flash and ambient light) with the Luna-Pro F in the flash mode.
2. Measurement of the ambient light with the LunaPro F in the ambient/daylight mode.
3. Compare the different F-Stops indicated for a shutter speed of 1/125th second in flash and ambient modes.4www.butkus.org

Any difference between the two readings calls for an f/stop modification as shown in the table below.4www.butkus.org

1. Combined measurement (flash and ambient light) with the Luna-Pro F in the flash mode.
2. Measurement of the ambient light with the Luna-Pro F in the ambient/daylight mode.
3. Compare the different F-stops indicated for a shutter speed of 1/125th second in flash and ambient modes. Any difference between the two readings calls for an f/stop modification as shown in the following table:

Example:
Luna-Pro F indicates f8 for a flash reading and f5.6 at 1/125th second for an ambient/daylight reading. The difference (f8 and f5.6) is one stop. If the shutter speed to be used is increased to 1/500th second the table below indicates that the lens must be opened up by 2/3 stop from the reading indicated by the Luna-Pro F. The higher the shutter speed (1/500th second vs. 1/125th second) will decrease the ambient light contribution to the exposure. Opening up the lens 2/3 f/stop will increase the ambient light contribution, bringing the ambient/flash ratio back to the original.

II. n. Color Crossover
The proceeding discussion concentrated on the effects that lighting can have on film, either black and white or color. However, with color, three separate emulsions are on the film each of whose individual response may be different. In normal exposure situations all three layers will track reasonably well, resulting in accurate rendition of color as well as density. However, at the extremes of exposure levels, deviations in the characteristic response of individual color layers of the film can result in a condition called color crossover. This condition results in a color shift in an area of under or over exposure that cannot be corrected without affecting the colors of the properly exposed areas of the scene. It is therefore very important to avoid this condition which shows itself as color shifts in the shadows and highlights.

II. o. Zone Systems
There are times when the lighting range cannot be brought within the acceptable limits of the film because of an inability to fill or use "gobos" (as spelled in manual) such as when photographing landscapes. When these situations arise, the exposure levels can be adjusted so that the most important parts of the scene receive proper exposure. This can be done with either black and white or color film. However, some detail, either in the highlight or shadow areas, will be lost.

When using black and white film, another technique is available to extend the capabilities of the film to record extreme lighting ranges. It is called the zone system. Instead of relying on standard measurement and exposure techniques, the zone system combines special measurement techniques, modified exposures, and altered film processing to expand the range of light values that the film can accept. In doing so, detail can be recorded which would otherwise be lost.

A complete discussion of this technique is far beyond this manual. References are given in the appendix which should help you become familiar with this very useful photographic tool.

The Luna-Pro F is well suited for use with most zone systems because of its null meter principle of operation and the zone system scales (20). Most systems are based on a central zone, representing a certain lighting level called Zone 5. From this level, the range of light from highlight to shadow is measured and referred to this central zone. The level of variance from the central zone determines the amount of exposure correction and processing modification, if any, that is needed. With most meters, the zone equivalents must be marked on the face or transferred to another sheet to correlate with changes in light level. However, with the LunaPro F. the computer dial can be used to adjust the meter needle at any light level. Any subject can be nulled for and light variations from that level read in zone system values I thru IX directly off the meter face in EV. This means that you can always set null for Zone 5. Or, you may wish to bias the reading in one direction.

Simply turning the computer dial of the Luna-Pro F allows you to put the meter needle anywhere from -3 to + 3 EV from a normal value.

To use the zone system scales of the Luna-Pro F. take a measurement of a central zone (Zone V), noting the corresponding EV values for each zone value. Using the EV scale as a reference point, measurements of highlight and shadow areas can then be translated into zone values.

Example:
Take a reading of a central zone or mid-tone (Zone V) and null the meter. Assume the EV indicated for Zone V is '8'. Note the EV values indicated for the other zone values. In this example:

Zone I = EV 4   Zone VI = EV 9

Zone II = EV 5   Zone VII = EV 10

Zone III = EV 6   Zone VIII = EV 11

Zone IV = EV 7   Zone IX = EV 12

Zone V = EV 8

Now you can take a reading of a highlight area, null the meter and note the EV indicated. Assuming the highlight reading corresponds to an EV 12, the zone value would then be Zone IX (see chart above). Now take a shadow reading, null the meter and note the EV indicated. Assuming the EV value is '5', the corresponding zone value would be a Zone II.

The zone system scale of the Luna-Pro F enables you to easily measure zone system values and establish information regarding tonal range in a scene.4www.butkus.org

In the example above, Zone V (a mid-tone) is used as a reference point; however, with the Luna-Pro F you can select any zone or light level as a reference. A reading is taken of a particular area, the meter is nulled and the EV value noted (i.e., EV = 7). If you would like that area to be represented as a Zone III rotate the computer dial until EV 7 is directly above Zone value lilt At this point, a reading of the appropriate apertures and shutter speeds will render the particular area measured as a Zone III.

With a little practice, you will be amazed at the ease of obtaining this specialized information.

11. p. Film Reciprocity Failure
All photographic exposure meters rely on a principle of film exposure called reciprocity, to function properly. Basically, the film integrates or adds up light during exposures to produce the latent image. Within certain limits, the same image density is achieved for short exposures of high intensity as with long exposures of low intensity, as long as the product of intensity times time is constant. When the exposure times get very long or very short, however, this reciprocity effect is lost, and an accurate prediction of exposure, and color balance with color films, cannot be determined solely by the meter reading. It is therefore important to check the instructions supplied with the film in use to determine when reciprocity failure can be expected, how severe it will be, and how to correct for it. Here again the Luna-Pro F greatly assists in exposure determination because the corrective filters suggested by film manufacturers to adjust color shifts from reciprocity failure have an effect on exposure. These filter factors can be programmed into the Luna-Pro F and the new, corrected f/stop read directly.

11. q. Intermediate f/stops
The Luna-Pro F is calibrated in 1/3 f/stop increments with numerical indications at full stops. A table is included below with the actual numerical values of the 1/3 stop increments listed for levels from f/0.7 to f/128. Values not listed can be calculated from the formula that follows.

For example, if you wish to stop down 1/4 stop from f/4, take the square root of 2:  which equals 1.414 and raise it to the power.25 which is the decimal equivalent of 1/4 stop.

11. r. Intermediate Footcandle Values and Exposure Times
Calculation of intermediate values of foot candles and exposure times is basically the same as calculation of intermediate values of f/stops except that the value square root of 2 is replaced by 2 in the formula.

For example, you have a foot candle level 1/2 stop above 700 as represented on the chart on the back of the Luna-Pro F.

New footcandle level = (old level) (2(f/stop change)) 
                                = (700) (2( ))
                                = (700) (1 .41 4) = 990

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