Nikon FX and DX difference

I did a lot of research on the difference of Nikon DX-format and FX-format cameras. What I found was astounding and somewhat shocking to me. Here are the links if you decide to read and understand, but I will try to summarize as clearly as possible after the jump.

http://www.kenrockwell.com/nikon/fx-dx-future.htm
http://en.wikipedia.org/wiki/Nikon_f_mount
http://www.youtube.com/watch?v=u2_iRW9qpRw&feature=related

Alright so here it goes: The main difference of an FX and DX camera is the size of its sensor. FX-format cameras, also fondly known by the name full-frame DSLR obviously uses full-frame sensor. A full-frame sensor is almost double the size of a half-frame sensor. DX-format cameras uses half-frame sensor, which are cheaper to make, hence cheaper and smaller DSLRs.

Some of the examples of the FX line includes the Nikon's flagship - D3, D3S, D3X and the recent D700. DX line is the more consumer-priced cameras like D40, D60, D80, D90, D3000, D5000, and the biggest surprise, D300.

When DX cameras were launched, Nikon decided to make a range of DX lenses. You can differentiate them by looking for the DX logo on engraved on the lens. DX lenses are smaller and lighter, just to cater for DX cameras. If you mount a DX lens on an FX camera, due to the smaller rear mount (or hole for light to enter the camera), it will make a small picture on the sensor and black shadows around it (vignetting). It is like the picture below, you will see image in the red box, but whatever outside it will be black.

35mm film marked with Nikon sensor sizes.

(Green: FX, full-frame, Red: Nikon DX.)

However if you mount an FX lens on a DX camera instead, it works just fine!
But here is the catch. Due to the design of DX camera, there is a 1.5x focal length multiplier to make it behave more like a FX camera. For example: if you have a 18-55mm lens (which Nikon always gives as a kit lens for entry level DSLR), when mounted on a DX-format camera, it gives an actual zoom of 27-82.5mm.
More examples: if you decided to get the 35mm f/1.8 pancake, it actually makes a 52.5mm instead. An 18-200mm lens actually does a whooping 27-300mm zoom when mounted on a DX camera!

Hence if you want to get ultra wide-angle like 18mm or less on your DX-format camera, you just have to buy a lens which can reach 12mm or lower. Usually lens like this are ultra expensive.

***Quick-fact 1: Our eyes have a focal length of ~22mm.
***Quick-fact 2: Due to smaller sensors and smaller lens in compact cameras or even our phone cameras, they usually have larger focal length multipliers of up to 6x. Even the latest micro four thirds like Panasonic GF-1 and Olympus EP-1 have focal length multipliers of 2x. (Refer chart below for comparison of sensor sizes)



So there you go. Any questions or mistakes try voicing out on my Cbox. =)