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Yes,
The effective aperture is 40mm and the effective focal length is 400mm, hence it stays at f10.
If you remove the PST etalon for a PST "mod" - the ideal donor scope is an f10.
If you put the etalon say into a 150mm f6 scope (900mm focal length) you'll end up with an effective aperture of 900/10 =90mm!
Much cheaper to use a 90/900 scope in the first place!
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