Close-up lenses for model S3 and S4

Close-up lenses

For the Hagner Universal Photometer, model S3 and S4

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:

A.

Focal length 500 mm

(2 dioptres)

B.

Focal length 250 mm

(4 dioptres)

C.

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, model S3.

Lens combination Focal length (mm) Measuring distance* object-lens approx mm Correction factor (F)
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.