New camera, or a new lens? Help...

Stephen_H wrote:

The auto focus is leaving me missing a few candid family photos.

While an upgrade in camera and lens will give an improvement, if your photos are indoors without flash any system is going to struggle.

Poor light leads to poor autofocus speed and accuracy. A slow (aperture) lens like the 18-55 will only make this worse.

It has already been mentioned that indoor without flash, means wide apertures and slow shutter speeds which in turn means narrow depth of field and motion/camera blur. Bumping up the ISO on a newer model like the KP will give better results than doing the same on your current camera.

But I think the biggest change you can make will be to get an external flash. Look for something that will work in P-TTL mode with your Pentax like a second-hand AF360 or AF 540. Add a flash diffuser like a Gary Fong light-sphere. Then spend a little time with online resources to learn about how flash works generally. You can even use your on-camera flash together with the external flash sited away from the camera and triggered optically.

This was probably not the answer you were expecting, but once you take control of the lighting yourself you do not have to worry about a slow shutter speed or a too wide aperture. The flash exposure in the order of 1,000s of a second and will freeze any action. You will be able to use the 18-55 lens stopped down to f8 or f11 so you will have enough DOF if you need it. Your current camera and lens (stopped down) is quite capable of producing excellent images. I fear buying new camera/lens will not give you what you want.

Flash is a steep learning curve but is well worth the effort.