Can someone explain the meaning of the zooming-factor(ZF) of a camera. These ZFs are refered to what values?

Question

Does the optical zoom base on the certain focal distance of the object, say 2.5 meters ? Does digital zoom increase or increase the number of pixels per an area if we choose to have a digital zoom of 3?

Answer 1

The thing to look for is the optical zoom range in mm. For example: 35-105mm.
The small number tells you how wide you can zoom and the big number tells you how close you can zoom in.
When you devide the two, you get the zoom factor. In this case 105/35= 3
Optical zoom is what the lens does - with no cost to image quality.
Most cameras also have digital zoom, but this is achieved by discarding pixels along the edge of the picture and magnifying the central part via software. So with digital zoom, you do lose image quality. The use of digital zoom is generally not recommended. I'd actually even ignore the digital zoom in my buying decision.
A zoom range of 35-105mm is pretty good for most stuff. I personally like the wide end of the zoom to be even better - say 28mm - so I can get more in the frame with indoor shots, etc.
And if you like to zoom in on small details from far away, you should concentrate more on the higher number. Some 10x zoom cameras go up to 400mm. With these super zoom cameras, you'll want a model that has image stabilization, because anything over 300mm otherwise requires the use of a tripod.

Answer 2

The optical ZF is the ratio of the focal length of the highest telephoto zoom setting to the lowest wide angle zoom setting.

For example, if the optical zoom specs say 35mm to 105mm, then

ZF = 105 : 35 = 3

Marketing material calls this a 3x Zoom.

Digital zoom is completely different. There is no real "zooming". It is just an electronic technique to make the pictures subject look closer/larger.

The best digital zooming technique works like cropping; it shows you a subset of the original pixels in a lower resolution image.

The worst digital zooming technique works like resizing to a larger pixel count; it stretches the original pixels farther apart and invents new pixels based on the surrounding original pixels. This preserves the original resolution count, but blurs the image.

Good Luck