You asked
Is the pentax k r good in low light?
The K-r's page doesn't give its high-ISO results, so I can't tell you how clean it is at, say, ISO 3200. What I can say is that it has an APS-C sensor, and a bigger sensor collects more light, so full frame has roughly a stop's advantage over APS-C. The sensor guide explains the trade-off.
Lens choice does more for low light than the body anyway. The K-r has stabilisation in the body, which helps you hold steady at slow shutter speeds, though it won't freeze a moving subject. For dim rooms, look at fast primes from the K-r's lens list:
- Pentax smc DA 50mm f/1.8, a cheap, sharp choice
- Sigma 30mm f/1.4 DC HSM Art, a fast standard-ish lens
- Sigma 35mm f/1.4 DG HSM Art, when you want more light
Primes gather far more light than kit zooms, which is why I'd start there, as the lens guide explains.
Written by Claude from this site's pages.