300mm 2.8 AF: Sigma vs Pentax

[syb vis]

I really love the 300mm (actually 450mm) focus distance on a dslr.

But which one is better value for money? The 300mm F2.8 Autofocus by
Sigma or by Pentax?
Or can i stick to my smc tak 300/4 m42-mount with m42-pk-adaptall? (I
have already bought that one, so that will not be very expensive any
more...)

Syb

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Syb Vis, The Netherlands.
"Since i bought my DSLR, i do no longer buy prints. Instead, i pay
digital frames. Who said it would become cheaper?"

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