How digicams has more optical zoom?
Like nikon p500 has 36X zoom and nikon D5100 with 18-55mm lens could have less, what is the major difference as i'm starter
Well, here's the thing. An 18-55 lens would have an optical zoom of 3x (55/18=3.055). But a lens like a 100-300 would also have an optical zoom of 3x. So focal lengths are used to show how much 'zoom' a camera has because different lenses have different purposes.
For example, an 18-55 lens covers wide to short telephoto for general use, while a 100-300 is a telephoto lens for things that need more reach like wildlife or sports.
It seems that you do not understand the huge differences between a P&S camera that does everything for you and limits you to using the single lens that come permentatly attached to them and a dSLR camera which is a fully adjustable camera and requires the user to know how to control exposures and choose the various lenses needed to shoot various subjects.
For instance I have two 2x lenses. One is a 12-24 mm wide angle lens and the other is a 200-400 mm telephoto lens. Their 2x status has NO relationship except when you divide the longest focal length by the shortest, the product is the "x" factor
These are really never a big consideration when choosing the proper lens for the subjects you intend to use. One of my most used lenses, a 18-200 mm is a 11x lens if you do the math, but nowhere on the lens does it say 11x. My other most used lens is a 300 mm f/2.8 which is a prime lens and would be describes as a 1x lens if you were to need that information
Basically, optical zoom ranges are only a consideration when buying a P&S camera. When buying a dSLR, the focal lengths are what are important