Absolutely
The Shot - fictional short
Shot on Pentax K-5 on Pentax-M 50mm 1.4, Sigma (manual focus, auto aperture) 24mm f2.8, Pentax-A 100mm f4 macro, DA 16-45mm f4.
Etoile - music video
Shot on two Canon 550Ds with Pentax-M 50mm 1.4 and Pentax-A 100mm f4 macro (using an $10 adapter) and some canon lenses (EF-s 28mm 2.8 and 18-135mm f3.5-5.6).
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No Sane Man Will Dance - fictional short
Shot on Canon 7D with Pentax-M 50mm 1.4 and Pentax-A 100mm f4 macro ($10 adapter), a $60 unbranded 400mm f6.3 (for one very long shot!) and a Canon EF-s 17-85 f4-5.6 (for the wides!)
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I also use a lot of different cameras! The K-5's mine, but a lot of my film making friends have Canon and I find it generally preferable to shoot on as it has full manual control. Come on Pentax, release a patch...