Stopping down an imaging lens improves image quality – most of the time. When stopping down too much, the image quality gets worse again. This short article gives a simple intuitive explanation of why that is and when it makes sense to stop down and when it does not.
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Telescopes form images of infinity-foused objects and collimators project objects to infinity. Sounds simple, is simple. Except when it comes to distortions. Telescopes and collimators create the strangest “distortions” (like keystoning), that really are projections.
High-accuracy MTF measurements are performed with high-cost, high-maintenance diffraction limited objective lenses. These systems are certainly good solutions for R&D, but often not so much for volume manufacturing, where cost and risk are equally as important as measurement accuracy. Using affordable non-diffraction limited optics is a viable solution, since they are much more scalable whilte not compromising measurement accuracy too much. This short article describes the accuracy loss with easy-to-use formulas and proofs them with intuitive examples.
Colour measurement devices often claim to rely on the quality of their calibrations. However, no matter how good these calibrations are, the quality of the measurement is ultimately constrained by the quality of the hardware. It is not possible to just “calibrate away” suboptimal hardware. There is only so much a calibration can do. Using a simple white point calibration, one can easily see what these limits look like, where they come from, and what a calibration is actually doing.
A Köhler illumination is a way to create uniform illumination out of a non-uniform source. Most notably, Köhler illumination makes very little use of diffusers, thereby preserving almost all of the source’s optical power. This article shows how to design such an illumination scheme and gives tips and tricks on how to optimise the design.
Optical metrologists need homogeneous light sources. Without them, it is difficult to measure the quality of optical systems accurately. Though commercial solutions are an option, they are often expensive. Their high prices are usually not a problem if one needs only a few of them. However, if they are parts of mass-produced products, then their high prices are a problem. In such cases, it is preferable to build one’s own customised light sources. This post shows how to design such a customised light source and uses an easy-to-follow example to demonstrate all steps in a complete optical design. Only standard components and simple manufacturing techniques are used.