Winlens lab instructions

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Geometric MTF The Modulation Transfer Function (MTF) is a measure of how contrast is preserved in the imaging process. Modulation (or contrast) is defined as Modulation = M = I !"# − I !"# I !"# + I !"# , and the MTF is defined as the ratio of the image modulation to the object modulation, i.e. MTF = M ! M ! . The object can be envisioned as a superposition of sinusoidal gratings of different spatial frequencies. Each sinusoidal component is affected differently by the imaging system (the image modulation deteriorates for high-frequency components), and accordingly the MTF is a function of spatial frequency. To view the Geometric MTF diagram • click the MTF icon on the graphs tab In this double diagram, which is shown in Fig. 7, you find on the left hand side the MTF in the Gaussian (paraxial) image plane. The horizontal axis corresponds to spatial frequency. The scale is set in the text box below the graphs. WinLens, by default, sets the scale to the cut-off spatial frequency of a
diffraction-limited system 13 with the same numerical aperture as the current system. As in the spot diagram, the rows of graphs correspond to the different object points. On the right hand side you find what WinLens calls the Thru MTF, i.e. the MTF for a specific spatial frequency, in planes in front of and behind the Gaussian image plane. The horizontal axis corresponds to the distance to the Gaussian image plane, known as the defocus. In the Thru MTF diagrams, you can see in which plane you have maximal focusing. For Thru MTF, WinLens uses the half cut-off frequency by default – you have to choose a reasonable frequency yourself - for instance 100 cyc/mm for a camera objective. For further information on the MTF graphs, see Help (press F1). Chromatic Aberration Chromatic Abn: EFL/BFL displays the longitudinal chromatic aberration, i.e. the focal length as a function of wavelength. To open the Chromatic Abn graph, • click the COL icon on the Graphs tab of the toolbar. You can choose between effective focal length (EFL) and back focal length (BFL). Numerical values are given for the five wavelengths that can be set on the Waveband tab of the System Parameter Editor. 1 The cut off frequency of a diffraction limited system (where the MTF approaches zero) is
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Page 3 and 4: Please note that the teaching assis
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Page 19 and 20: a. Choose (on the Conjugates tab) F
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Winlens lab instructions

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