Foto- (en film-) camera's zijn al sinds mensenheugenis voorzien van ingebouwde meters om het invallend licht te kunnen bepalen.
Waar het eerst slechts een indicator was is het nu een compleet geautomatiseerd systeem dat sluitertijd, diafragma en filmsnelheid aanpast.
Echter, soms is het handig om een externe meting te verrichten bijv. als de camera op het statief zit en het onderwerp echt van dichtbij gemeten dient te worden.
Daartoe heb ik sinds ca. 1975 een Gossen Sixtar lichtmeter, anno 1966(!!), in bezit.
Gossen Sixtar lichtmeter
The 1966 Gossen Sixtar (in US Super Pilot) exposure meter was a derivative of the Lunasix, apparently aimed at the advanced amateur.
The Sixtar has a display with match needle instead of luminance scale, making it easier to use.
The Sixtar measures continuously, there is no power switch. The match needle is aligned over the reading needle and then corresponding aperture and shutter speeds read from the scale.
For low light, the button is depressed to activate a reduced scale. In extreme low light, this button can be depressed further to lock the reading needle.
|Type||Hand held exposure meter|
|Sensor||CdS (Cadmium Sulphide)||SBC (Silicon Blue Cell)|
|Measurement||Ambient reflected & incident|
|Sensitivity||-6 to +24 LV|
|Display||Moving needle + Match needle|
|Aperture||f 1 to f 45|
|Film Speed||6 to 12,500 ISO / ASA|
|Time||1/2,000s to 2 hours||1/2,000s to 30 minutes|
|Power||2 x Mallory mercury cell / 1 x Varta V625PX / 1.5V|
|Dimensions||95 x 71 x 34mm|
Setting the film speed
|Rotating the selector disc (6) by its actuating bosses until the number of sensitivity of the film used is shown in the scale of sensitivity DIN (13) or on the ASA (ISO) scale (5), coinciding with the mark fixed to the reading window.|
Measures the reflected light
|Push the diffuser cap (1) bottom left or right until net snap.The SIXTAR is ready for operation.
To measure the reflected light exposure meter will be directed to the object to be photographed in the direction of the arrow.
Measurement of the incident light
Placing the diffusing cover (1) exactly in the center front of the measuring gap.
The SIXTAR is ready to run right snap.
To this end the meter will be directed to the camera, in the direction of the
red arrow in the illustration.
The drag needle (9) SIXTAR is mechanically coupled to the computer.
Turn the knurled ring (4) so that the needle (3) of the galvanometer passes exactly through the center of the white ring on the follower pin (9).
Then read on the scale (10) and (11) a combination of exposure time / appropriate diaphragm.
The exposure index appear red numbers on the scale (13). For film, diaphragm use reads vis-à-vis the rate of shooting (12).
RED BEACH corresponds to a "forbidden area" which means that if the needle is in this area should be engaging another measurement range.
Thus if the white of the meter needle is in the red left field, it will be necessary to press the switch (2) measurement range of up to perception of a clear resistance. If, however, on the occasion of a new measure, the needle of the device is in the red field on the right, it will then return to the previous measurement range by simply releasing the switch (2).
BLOCKING THE NEEDLE in low light becomes possible by first pressing the switch (2) measuring range up to perception of a clear resistance; leave the needle to stabilize and continue to support.
The needle of the meter is found then blocked, which can adjust the drag pointer and read the indicated values.
Batteries / Piles
The batteries (or battery) used are of the PX 13 MALLORY (2 pcs) or Varta V625PX (1 pc.) kind, whose life depends on the current consumption. Battery life of 1 year (Mallorry) or even 7 years (or longer with the Varta) is possible if care is taken not to open the case of this all-ready light meter if not during measurement operations.
One should frequently check the battery voltage. Their replacement is necessary when the meter needle moves away from the yellow mark (8) upon actuation of the pushbutton (16). In this case, open the battery compartment by turning to the left, pressing lightly. Check the new batteries following the steps above.
The zero adjustment of the needle is performed by removing the batteries. The needle should then be on the left edge of the red zone. If it is not so, returning the meter needle to the correct zero position by turning the zero adjustment screw located in the lower part of the device.
The back of the table gives the values rounded SIXTAR in LUX (worldwide) and FOOTCANDLE (US only)
(ft-c) - 1 FT-C = 10.76 LUX corresponding to the reading on the dial in the event of measurement of the incident light.
Despite this, the SIXTAR can not be used as a true light meter, because illumination, for example in lux or footcandle, by definition can not be measured on a flat surface.
The SIXTAR indeed uses a diffusing sheet that better captures the entire light that is the photographic point of view.
Different topics are usually embossed sets that receive light from many directions: sun, sky, reflections of houses, trees, soil, etc ....
It is only if the one receives a directed light beam (projector) you can use the table values in practice to measure the illumination.
For measurements of the reflected light, it can not indicate values in lux, as measured by the light reflected from the object.
Measuring the reflected light does not determine the illuminance as the measurement of the incident light, but the luminance. Luminance indicates the amount of light emitted per unit area (luminance unit is the apostilb, abbreviated asb).
The measured values for the measurement of the reflected light, expressed as asb are approximately 7.5 times lower than the values in lux for measuring the incident light.
It has, for example:
|lux measurement of the incident light 18 ° DIN||0.7||1.4||2.8|
|asb (measurement of the reflected light)||0.095||0.19||0.38|
Indications for reading
The old exposure time '2,' 4 '8 ... represent fractions of a second, that is to say, 1/2, 1/4, 1/8 sec. etc. ...dropoff Window
Details relating to the implementation of measures
The SIXTAR measures light understood as a nail, which is returned by the object to be photographed.
The indication raised does not only depend on the light intensity but also the colors and reflective objects.
The lighting remaining the same, the needle will deflect more strongly if the meter is directed onto light objects and more weakly in the case of dark objects. The meter totals the partial clear details and responds to an average value.
In some cases contrasts clarity or particularly strong color, it is preferable to perform the measurement on the part of the most interesting object of exposure viewpoint. Black and white, it is usually in the dark part that we would like to distinguish certain details; in color photos, for cons, it is usually clear parts in which we want to see a good modeling. It is therefore necessary to approach some of the object to be photographed, but avoid your shadow or that of SIXTAR is not projected on the object. This method is known under the name of "close measurement" (Nahmessung).
The angle measurement SIXTAR, limited to 30 °, is one of the particular advantages of this meter. It allows highly accurate and effective action. The opportunity to contrast the different subjects or objects to be photographed up the SIXTAR at the forefront of exposure meters.
The needle of the mobile unit indicates the distribution, uniform or not, the brightness of the object.
In the measurements carried out from the object towards the camera, the SIXTAR fully enters the light incident on the portion of the object facing the camera, without taking account of the reflectivity or color of the object.
When photographing is hardly visible details, conduct the measurement of the incident light into an equivalent point, that is to say, benefiting from the same illumination. To measure, do not direct the SIXTAR directly on the camera, but in parallel to a line connecting the object to the camera. This method of measurement of the incident light into an equivalent point must often be used as, for example, for taking open air photos. Therefore, if you have the same illumination at the location of the subject, as that of the device, simply turn around and take the measurement with your back to the photographed object.
Schwarzschild effect (emulsion / roll-film only)
Photos obtained under low illumination require long exposure times (requiring the use of a foot). This fact leads in films from all sources, the effect Schwarzschild said: times measured for the shot must be extended to prevent underexposure.
Various qualities of films, that exhibit a more or less pronounced effect. This is why it is not considered on the scale of SIXTAR. For all color film, the Schwarzschild effect can further cause shades offsets (colors rendered falsely) that require compensation by special filters.
Some types of plans are accompanied by film features and instructions on shooting time prolonged pose. In other cases we recommend to go to a specialized laboratory color work or film manufacturer.
Maintenance / handling
The SIXTAR is a very sophisticated device, built and calibrated precisely. The photo-resistant new type of an element which is provided with this unit allows exceptional performance. So it should not be unnecessarily exposed to light, if you want it permanently ensures a proper job. Limit the duration of measures towards the sun, the strictly necessary.
When not in use, leave your SIXTAR rest in its case to protect from light. Indeed, photo-resistant element is not subjected to actual change in its properties, when it is subjected to the action of light, but has a sort of prior illumination memory. Greater measurement accuracy will be obtained when the previous illumination has been nil.
You can control yourself the proper functioning of SIXTAR by checking the battery and setting the zero.
Additional tests, for example, comparative measurements with a meter of the same or a different kind, are not feasible with sufficient accuracy without special devices (optical bench).
In the event that your SIXTAR fails, do not try to repair it yourself. Return it immediately, or if you like fifty years later, to your photographer. ()
Frank december 2014