Tests for visual determination    

In order to determine visually the resolution values reticle group tests have proved to be a very good investment. Depending on the system to be checked, those tests are available with different frequency ranges and different grading.

For the examination of intensifying foils tests with reticle groups arranged in only one direction are sufficient: system faults of different directions are not to be expected, geometrical faults dependent on direction will not have any influence on the test, as the tests are put directly on the cassette.

When checking optical relay systems where different resolution values of tangential and meridional direction due to specific optical aberrations can be expected (for instance in RGB systems) it is advisable to use tests with dense reticle groups, vertically arranged to one another.

In order to avoid reading errors due to the so-called pseudo focus, the number of test group bars visible in the picture should correspond with that of the test. A special form of the group test is the broom test with its continually changing local frequencies. With ist aid reading errors due to pseudo focus can surely be avoided.

To avoid Moiré-effects and the resulting reading uncertainties when using a stray radiation screen it should be taken into account to arrange the reticle groups under an angle of 45° to the segment direction of the stray radiation screen.

Tabular description

Tests for photometric measuring of the exposures     

For photometric measuring - and determination of the modulation transfer function (MTF) of a transfer system - tests without gaps between the single reticle pairs or reticle groups were developped in order to avoid measuring errors caused by vicinity effects. To obtain a constant measuring reliability over the whole frequency range, the values drop to the same extent after reaching the highest local frequency (compare tabular test description).

Tabular description

Tests for focal spot determination     

With the aid of a star test (or a sector star test) exposure, the size and form of a focal spot can easily be determined. This method takes less trouble than the slit or pinhole camera method and is sufficient for the solution of many problems, on condition that there is an approximately ideal intensity distribution.

The focal spot expansion l ensues from the formula


    a     =star angle (see tabular test description)
    d     =diameter of the blurred figure on the test exposure
    m     =scale of exposure (= star diameter of the exposure : star diameter of the test); for focal spots 0,6 mm an exposure scale m = 2 proved to be good.

Tabular description


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