According to
this thread, the 18-200mm covers APS-C only (this is hardly unexpected), but the 10-20mm does cover FF, with some vignetting, at and above 14mm.
As for the 17-50mm, it's the same boat, though it covers more of the frame at longer zoom settings.
In a practical setting, you may be able to use the 10-20mm for wide-angle shots as long as you can settle for a little bit of vignetting. You'll want to get a full frame compatible walkaround lens to replace the other two (the Pentax D FA 28-105mm would be a great candidate).
Adam
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