This is a Pentax lens that comes with a Pentax K mount. If you want to use a filter on the lens, then the filter size is 86 mm.
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Pentax D FA 150-450mm F4.5-5.6 ED DC AW
The Photography Shop
Pentax HD PENTAX-D FA 150-450mm F4.5-5.6 ED DC AW Lens
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