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For Simulens to work, setting an Aperture Map is mandatory as it describes the shape of the diaphragm.
The Obstacle Map is optional but adds more variation to the effects.
After setting the Aperture Map, you have to activate the Diffraction option. This is also mandatory if you want to see the interference patterns (glare). Deactivating it, disables the glare (but not the Scattering or Devignetting effects).
Play with Diffraction and Frequency levels to get the desired effect.
The Scattering effect is independent of all the above and creates a more general bloom in the image.
The Devignetting effect is also independent of all the features described before. It allows to reduce or increase the natural darkening of the images at the corners that occur when the angle of the lens gets wider.
Here is a general tutorial about Simulens.
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The SimuLens adjusment panel
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