Close-up lenses for model S3 and S4

Close-up
Close-up lenses

Measuring the luminance of small surfaces.

The Hagner Universal Photometer can be provided with close-up lenses for measuring the luminance of small surfaces at short distances, for example text on data terminal screens, without troublesome light loss.

The close-up lenses are available in sets of 3:

  1. Focal length 500 mm: (2 dioptres)
  2. Focal length 250 mm: (4 dioptres)
  3. Focal length 125 mm: (8 dioptres)

The lenses can be used separately or in combination with each other.

The following table applies when using close-up lenses with the Hagner Universal Photometer.

Lens combination Focal length (mm) Measuring distance* Object-lens approx mm
A 500 500 1.11
B 250 250 1.11
C 125 130 1.11
A + B 167 170 1.23
A + C 100 100 1.23
B + C 83 85 1.23

*The measuring distance is equal to the distance when the object is seen sharply through the view-finder. Lense combination is counted from the instrument and outwards.

When close-up lenses are used, the lumiance (L) of the object is obtained from the following equation:

L = F x LM where F is the correction factor from the above table and LM is the luminance measured with the close-up lense mounted.

It should be noted that the luminance (L) is the average luminance of a cone with the object on the "top" and the surface of the outermost lens as a base.