ISO 9336‑3 specifies a method of testing telescopes in terms of imaging states aimed at making valid optical transfer function (OTF) measurements.
ISO 9336‑3 includes two annexes (Annex A and B) that provide information on the more recent techniques for measuring optical transfer function and methods of deriving image quality criteria from such measurement.
OTF tests also enable performance to be compared with that computed by the telescope designer and provide effective quality assurance tests of production specimens.
ISO 9336‑3 on optical transfer function is useful for:
Methods of assessing the imaging quality of telescopic systems can be found in ISO 14490-7. The methods described in ISO 9336‑3 are basically subjective, relying as they do on the judgment of the observer and the quality of his vision. The technique of measuring the “limit of resolution” is relatively easy and quick to perform and provides a single figure of merit for each orientation of the test pattern. However, being a subjective measurement, it can be open to significant variations in its results.
When considering the details of tests in ISO 9336‑3, some features of the eye need to be borne in mind, especially its ability to accommodate for varying object distances and to adjust the working aperture, varying the iris size, according to the ambient illumination.
Integration of the system MTF over a certain domain of spatial frequencies and normalized to the diffraction-limited MTF will provide a single figure of merit that is a reasonable representation of the system performance without relying on any subjective assessment. When the spatial frequency domain is selected in accordance with the properties of the detector system the method can be applied to telescopic systems operating with any detector type, thus not limiting the method to visual observation. This is of importance as in state-of-the-art telescopes the same optical path can be used for visual observation as well as for wavelengths outside the visual range.
ISO 9336‑3:2020 supersedes ISO 9336‑3:1994, which is withdrawn.
The main changes are as follows:
ISO 9336-3:2020