Good to see you here, I hope you saw my thread, with my K-5 35 2.4 combo, just after I got the lens. It's a great lens for the money. The old 50 1.8s were a little faster, but sensor sensitivity more than makes up for it. I never shot film faster than 400 iso, I have no problem shooting 800 ISO in doors with my K-5. In fact if there's one thing I'd recommend, it would be, in low light set your user mode to TAV, set your shutter to 1/30 and your f-stop from f2.4 to f-5.6, and let the camera select the ISO. It's a great feature, and one that would be impossible to do on a film camera. It took me long time to clue in.
https://www.pentaxforums.com/forums/post-your-photos/182030-nature-introducin...35-f2-4-a.html