yes, you will be able to use your existing lenses
this info might be of use:
Pentax Lens Compatibility Chart
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Pentax bayonet lenses labeled "SMC Pentax" are referred to as "K" lenses in the table below. Other Pentax bayonet lenses have the lens designation as a part of their name as in "SMC Pentax-FA."
Note that "star" lenses work like their "non-star" counterparts: DA* lenses work like DA lenses, FA* like FA, F* like F, A* like A, and M* like M.
The Pentax Camera Lens Compatibility Chart
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Pentax K-Mount Lens Series Explained: The differences between various Pentax lens series
In a nutshell
There are several series of Pentax K-mount lenses; the ones currently being produced include the DA (digital), DA L (cheap digital kit), D FA (full-frame, digital optimized), and FA (full-frame) series. While all Pentax K-mount lenses ever produced are compatible with all current Pentax DSLRs (in some cases with restrictions in that not all exposure modes of the camera are supported by old lenses), there are significant differences between each lens series and each has different features. Furthermore some of the newer lenses do not work with older cameras. We'll be exploring the differences between the various K-mount series lenses in this article . . .
Pentax K-Mount Lenses Explained: The differences between various Pentax lens series
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be sure to check out options for buying " experienced " equipment from the Market Place " buy/sell "
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if you can fit one of the K 5 series into your budget it would be a great camera to start with
https://www.pentaxforums.com/forums/pentax-cameras-compared/?c1=Pentax+K-5&c...Pentax+K-5+IIs