Partially Coherent Defocused Imaging of Bar and Periodic Objects

Hild, R.; Nitzsche, G.; Kessler, S.; Leine, L.

doi:10.1080/09500348714550531

Cited by 3 publications

(1 citation statement)

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“…This topic has received further attention by Kirk [5] in the context of linewidth measurements with a microscope. Ichioka and Suzuki [6] studied complex periodic objects, and Hild et al [7] studied the behavior of the intensity distribution and its first derivative for amplitude, phase and amplitude/phase bars. They found that the asymmetric behavior of the first derivative is strongly correlated with σ and the phase content of the object.…”

Section: Introductionmentioning

confidence: 99%

Impact of partial coherence on the apparent optical transfer function derived from the response to amplitude edges

2017

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We present an investigation of the impact of partial coherence on optical imaging systems with the focus on whole slide imaging (WSI) systems for digital pathology. The investigation is based on the analysis of the edge response of the optical system, which gives rise to an apparent optical transfer function (OTF) that can be linked to two elementary complex functions Q and U. The function Q is directly related to the transmission cross coefficient (TCC) and can be identified with the performance function first introduced by Kintner and Sillitto. The function U depends on the TCC in a more involved way. When there are no aberrations the Q-function corresponds to the real part of the apparent OTF and the U function to the imaginary part of the apparent OTF. Close to the incoherent limit the effect of the U function is a mere shift of the edge compared to the fully incoherent case. We propose a new expression for the dependence of the depth of focus (DOF) on spatial frequency and on the partial coherence factor σ, and validate it by simulation. Partial coherence effects are investigated experimentally on a WSI system with a compact LED-based Köhler illumination unit with variable condenser NA. This unit incorporates a top hat diffuser for providing a reasonably uniform illumination field, with variations below 10% across the imaged field of view. The measurements of the apparent through-focus OTF derived from edges on a custom resolution chart for different σ were substantially in agreement with the simulations. Finding an optimal value for σ is not straightforward as lateral resolution and the level of edge ringing improve with increasing σ, whereas edge contrast and DOF improve with decreasing σ. We assess that the trade-off for the particular application of WSI systems for digital pathology is optimized for a σ value in the range of 0.55-0.75.

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Section: Introductionmentioning

confidence: 99%