News

Gossen Notes: How do I use the Micro attachment to measure at the microscope?

Wed, 03 Aug 2011 00:00:00 -0700

First of all, a reference specimen showing a common structure has to be laid under the lens. After having set the correct film sensitivity at the exposure meter, the exposing time to a freely selected aperture value is measured at the ocular take. Please note the measured time/aperture combination.

Then, an exposure chart is made with different times.

The set illumination must be continuous at all times.

After having developed the film, please select the result with the correct exposure. The time with which this photo had been exposed corresponds to an aperture value for the measured exposure. This aperture value is the reference value for all future measurings. So the corresponding exposure time is measured to this fictitious aperture value. Nevertheless, it is clear to make aperture charts which is due to the different microscopic illumination procedures, specimen structures and required image effects.

Gossen Notes: Why are there still hand exposure meters?

Tue, 05 Jul 2011 00:00:00 -0700

1. The hand exposure meter permits the incident light measuring whereas the implemented exposure meter may only read the reflected light measuring.

2. Many medium and large format cameras do not have an implemented exposure meter.

3. The hand exposure meter forces us to think.

Gossen Notes: Why does the Color Pro 3F measure three colors?

Mon, 06 Jun 2011 00:00:00 -0700

Depending on the light source, the color of the reflected light is composed by very different spectres.

Pure temperature beamers like for example bulbs (artificial light), the sun or candles have a continuous color spectrum which is being shifted between blue and yellow according to the temperature of the beamer. This is why it is defined as color temperature.

Light sources like gas discharge lamps do not "produce" the light energy from thermal energy but take it from other physical processes. Therefore, they do not have a continuous color spectrum but a line spectrum. The consequence is that there is also a shift to the magenta-green axis, apart from the blue-yellow shift. This shift may only be detected by means of a third measuring cell.

Gossen Notes: What is an exposure value/EV ?

Tue, 03 May 2011 00:00:00 -0700

To make the handling Time/Aperture easier, the exposure value (EV) has been introduced.

Each step on the aperture scale corresponds to one step on the time scale. To hold the light quantity constant, you also have to change the aperture after having changed the exposure time. The graduation of both scales each corresponds to a double or a half of the light quantity.

One EV always corresponds to a certain light quantity and thus to a firm time/aperture ratio. EV 0 corresponds to aperture 1 at 1 s. If the camera permits the setting of an exposure value/EV, it will be very easy to give priority to the shutter speed or to the lens opening without having to calculate again.

Gossen Notes: What is the difference between incident and reflected light measuring?

Mon, 04 Apr 2011 00:00:00 -0700

The incident light reading measures the light which illuminates the subject. The reflected light reading measures the light which is reflected by the subject.

For the reflected light measuring, please direct the exposure meter from the camera to the subject. For the incident light measuring, please shift the sphere (white cone) before the measuring cell, go to the subject and measure to the camera. This is to guarantee that all light elements (e.g. stray light) are taken into consideration. Thus, the result is independent from the grade of reflection of the subject.

In the reflected light measuring, a soot-covered chimney-sweep would distort the result as much as a white apron-clad baker. Only the mechanic in a neutral grey overall delivers the correct result.

However, the exposure value/EV which is given by the incident light measuring is correct for all three persons.