ISO 14490-10:2021 Optics and photonics — Test methods for telescopic systems —Part 10: Test methods for axial colour performance

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Optics and photonics — Test methods for telescopic systems —Part 10: Test methods for axial colour performance是于2021-02发布的ISO标准，适用于全球范围。

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Optics and photonics — Test methods for telescopic systems —

Part 10: Test methods for axial colour performance

1 Scope

This document specifies the test method for the measurement of the axial colour performance which includes axial chromatic aberration and spherical aberration of telescopic systems and observational telescopic instruments.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 14132-1, Optics and photonics — Vocabulary for telescopic systems — Part 1: General terms and alphabetical indexes of terms in ISO 14132

ISO 14490-1:2005, Optics and optical instruments — Test methods for telescopic systems — Part 1: Test methods for basic characteristics

3 Terms a nd definiti ons

For the purposes of this document, the terms and definitions given in ISO 14132-1 apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://w ww. iso .org/ obp

— IEC Electropedia: available at https://w ww.e lectropedia. org/ 4 Requirements

4.1 General

All measurements shall be performed on optical axis, i.e. the target shall be situated at the centre of the field of the specimen. The measurement principle relies on the evaluation of the best focus position for different wavelengths. Therefore the target size and structure have to be suitable to evaluate the best focus but do not necessarily need to contain a structure at the theoretical resolution limit of the specimen.

4.2 Test arrangement

The measurement of the axial colour performance shall be carried out with the test arrangement shown in Figure 1. It ideally consists of a negative back lit test target screen at the focal plane of a collimator. The light source has to be bright enough to guarantee sufficient luminance after spectral filtering. In addition a dioptric tester is used for analysis.

The test arrangement shall provide three different wavelengths: green (e = 546 nm), blue (F’ = 480 nm) and red (C’ = 644 nm). This can be realized with narrow band filters (full width half maximum <20 nm) either between test target and light source, after the test specimen or after the dioptric tester. The three different colours are used to determine the colour-dependent axial focal shift.

Key

1 light source 5 collimator lens

2 condenser 6 test specimen

3 diffusing plate 7 dioptric tester

4 test target screen with test target groups 8 spectral filter

Figure 1 — Test arrangement for the measurement of axial colour performance

The collimator shall have a sufficiently small axial chromatic aberration. For a rough estimation the chromatic aberration in dioptres times the square of the magnification of the test specimen should be -1

smaller than 0,05 m (dioptres). Ideally, reflective types of collimators [e.g. (off-axis) parabolic mirrors] should be used.

The dioptric tester shall have a sufficiently small axial chromatic aberration. In general, this should be -1

smaller than 0,05 m . See Annex A. Typically, dioptric testers with higher magnification of around 6× provide higher dioptre precision.

4.3 Preparation and carrying out of measurements

-1

As a first step the dioptric tester shall be set to 0 m and the eyepiece of the dioptric tester shall be focused for compensating aberrations of the eye of the examiner at green illumination. This will be done by using a faint diffusive plate in front of the dioptric tester and focusing on the dioptric tester’s reticle. The examiner shall focus from the positive dioptre side to avoid accommodation.

-1

The test specimen shall be focused to 0 m onto the test target located in the centre of the field of view. The so defined state is the reference for the following measurements.

As a next step the defocus of the test specimen for blue light shall be measured by refocusing the dioptric -1

tester. The result for the axial chromatic focal shift for the blue wavelength in m shall be noted.

As a last step the previous steps shall be repeated by using the red light. The result for the axial -1

chromatic focal shift for the red wavelength in m shall be noted.

For high precision measurements, the chromatic aberration of the examiner’s eye shall be compensated for at blue and red wavelengths as defined in 4.2.

4.4 Determination of results

As an overall result of the measurement, the focal shift of blue to green light and red to green light shall -1

be stated in m .

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