Final cut pro X , Importing AVCHD 50P

The current version should import this media without problem.

I have to desagree on this. FCPX cannot work with AVCHD files (.mts, .m2ts) directly. So FCPX is doing some sort of conversion during import.

I doubt that there is a conversion tool out there that can output better than an original. And only the original is truly equal with the ... original.

Than the only option left is that the converted files are somehow worst than the originals, depending on settings and viewer ability to distinguish the differences.

You will have to work with a software which do not convert but use the original files to get truly lossless.

I have to desagree on this. FCPX cannot work with AVCHD files

FCP has worked with AVCHD media since the day it was first released. The media is rewrapped to QuickTime, but the content is original H.264 and unaltered.

Final Cut Pro 7 - Apple's own website:

http://documentation.apple.com/en/finalcutpro/professionalformatsandworkflows/#c hapter=6%26section=2%26hash=apple_ref:doc:uid:TempBookID-ReplacedWhenAssociating WithMessierRevision-AVC-1041284

AVCHD footage is not captured natively but is transcoded to an Apple ProRes codec or the Apple Intermediate Codec. You can choose the destination codec in the Log and Transfer window preferences. For more information, see Choosing an AVCHD Destination Codec.

However, I cannot find similar info in FCP - X documentation. But why re-wrapping if it could work with originals?

That's obsolete and refers of the FCP7 and FCP6 versions. The current version of the software does not do this. When I said it has worked with FCP since it was first released I meant FCPX not legacy versions.