What is this difference b/w fx and dx lens?

I have Nikon d90 camera with 18-105 lens and now i plan to buy AF Zoom-NIKKOR 70-300mm f/4-5.6G (4.3x) without VR is it good cost around 6000/-

please tell me the difference b/w FX and DX lenses?

Added (1). But 1 of my friend have it hi said image quality is little poor?

Added (2). AF Zoom-NIKKOR 70-300mm f/4-5.6G (4.3x) without VR is it good? Cost around 6000?
but 1 of my friend have it, he said image quality is little poor?

FX is for 35mm film and full-frame cameras while DX is for crop sensor dSLR's. You can use FX lenses on either type of camera but you generally can't the other way around. That's because DX lenses were made to project on an image on a smaller area. This means, a DX lens will not cover the whole 35mm film frame and the full-frame dSLR sensor leaving a large dark fuzzy border around the tiny picture.

I have mixed feelings for the 70-300mm but it's a cheap lens that will give you lots of pulling power. If you badly need a long telephoto in a budget then that should be it. Shooting without VR at that length may bog you down but if you take the necessary precautions to eliminate blur, you will be able to maximize the potential of that lens. Just temper your expectations. Remember that in photography, you get exactly what you paid for.

I had a 70-300mm G lens. Today, it sits in a box on the shelf because one of the plastic parts snapped. Nikon made 3 different 70-300mm lenses and the G model was the cheapest and poorest in quality. They also make a D model that's a major step up, and the AF-S VR model that is excellent. Avoid the G model. I wish I had.

AS for FX vs DX, your D90, like most Nikon DSLR's is a DX camera, using a smaller sensor that the 35mm size used by FX models (D700, D3). An FX lens, having a larger diameter and lens elements to match, works perfectly with DX and FX cameras. A DX lens works perfectly with DX camera, but forces the FX camera to adjust down to a DX-sized portion of the FX sensor, lowering the image resolution.

One of the older AF Nikon 70-300mm lenses was a Tamron designed lens, and may have even been made by Tamron as Nikon sometimes does that to keep costs down of their low-end gear. This lens was produced in the early 2000s.

This lens is easy to identify as it had the focus ring at the front of the lens. Here is a photo:

If you friend is referring to that lens, he is correct. It's basically a Tamron lens.

I made the mistake of buying that lens, and while a bad lens, it was not up to the better Nikon lenses.