Is the pentax hd fa 43mm f 1 9 limited good in low light?

Yes, the 43mm f/1.9 is a good pick for dim rooms. Its f/1.9 aperture gathers much more light than a typical kit zoom, which is one of the main reasons to choose a fast prime.

Sensor size matters too. A full frame body has roughly a stop of advantage over APS-C at the same framing and aperture, so this lens is at its best on a full frame body. Good pairings from its catalogue page:

• Pentax K-1 Mark II if low light is your main concern
• Pentax KP if you want something smaller on APS-C

On APS-C, f/1.9 gives about the depth of field of f/2.8, so it still works well indoors. For the reasoning behind all this, see Sensor sizes.

Written by Claude from this site's pages.