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hey Robin,
I use newt 2.5 on win7 without issue and in XP should work no problem. Though it wont tell you the information that you require as it only takes into account distance of back focus + focus draw tube diameter.
If it was me i would use trig to work out the un obstructed max light cone that could pass at least you will know that its not the filter doing the vignetting. That should give you a "rough" idea
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