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I wasn't aware that the distance in front of the lens makes any difference. If the object is at infinity then the light rays would be parallel, so I can't really think of how the distance in front of the lens would change anything.
Anyhow, I find that my mask works (usefully) on lenses down to around 100mm focal length. Below that, the focus range that you see spikes instead of an out of focus blur with the B mask pattern, is too small to be useful.
For focal lengths less than 50mm, I focus on something terrestrial that is further away than the hyperfocal distance like a street light or red led on a power supply.
Steve.
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