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Here's an example of deliberately running an image orthicon well above the knee - a clip of Jim McKay, as part of a brief tribute on CBS Sunday Morning.
Note that the effect is very non-linear. It is much stronger in darkening the dark side of an edge than in brightening the bright side. This is because the redistributed electrons respond to the local fields between the target and collector mesh, and fall preferentially on the dark areas, instead of having a fixed pattern of redistribution (as a Gaussian sharpening filter or "unsharp mask" would have). Therefore, it cannot be simulated correctly with a linear filter.
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