This may be a very important point as to using this camera and lens:
Are you quite sure that the camera in the picture is a (Digital) DSLR. It looks like the K-Series film Pentaxes, does not look like the digital Pentax also named and labelled K-x, and the Pentax film SLR's reached their height of development with the Pentax KX, an outstanding film manual Single Lens Reflex (SLR)camera. But note the difference between nomenclature: Pentax KX and Pentax K-x.
The lens, a Pentax f1.7, is reputedly superior to the Pentax f1.4. The difference between the two maximum apertures is trivial. (I have these cameras.) I must ask the question: have you used the camera and does it take film or does it take a digital SD Card?
If it is a picture of the actual camera you have, then your question is important but the answer is simple. The lens is set for an f4 aperture, and the bokeh, circle of confusion, background blurring is maximized at that aperture. (Let's forget about the wider f1.7 for a moment.)
I have the Pentax KX film camera (had two but ran out of shelf space) and that lens, which is why I ask this question. If I am right, then it is a manual focus camera only and focus is completely under your control and bokeh, hyperfocal distance, etc., is also under your control. The new digital lenses don't even have a hyperfocal distance indicator ring. Why have one when hyperfocal distance is indirectly controlled by other settings?
As to your question, just about everyone else's answers pertain well to it. I just can't see how that camera can be used without film, and believe me, I feel a little older right now.