Hi, when using the optical zoom, the focal point is adjusted by moving optical lens back and forth and images are shown physically enlarged. Therefore, there is virtually no deterioration in the image quality.
When using the digital zoom, digital images captured by the image sensor of the camera are enlarged by digital signal processing. These signals are created by estimating the data from the surrounding pixels. Therefore, as the magnification level increases, signals to be estimated increase and image quality is deteriorated. Regarding low light shooting, Dawn, dusk, and everything in between, you get clear, natural results thanks to a wide ISO range from 125 to 6400. Let Auto ISO mode determine the best setting, or tweak the ISO yourself. I hope this helps. Dave