FX vs. DX (CX at bottom)
Digital SLR cameras are split into two categories, DX and FX.
Those two terms refer to the sensor size of the cameras image sensor.
I am not going to explain why one sensor is better than the other in this article because there are numerous variables to determine which size sensor is really "better." I am simply going to explain the relationship between DX and FX sensors and DX and FX lenses.
A FX camera (or more specifically, the sensor in the camera) is often called a full frame camera or 35mm.
When film was used, the film size was about 35mm so a full frame (or FX) camera sensor is about 35mm.
Most cameras today use an image sensor that is slightly smaller, often called a DX camera.
A DX camera is also called a crop frame or APS sensor.
To most beginning photographers, FX vs. DX will not affect them at all.
It is not until one ventures away from the kit lens that FX and DX matters.
We will start with a picture
A DX sensor is smaller than an FX sensor.
Both DX and FX lenes produce an image just big enough to fill their sensor.
If you put a DX lens on a FX camera, the DX lens will not produce a big enough image to cover the FX sensor.
It would look like this.
If you put an FX lens on a DX camera, the image produced by the lens would be a lot larger than the sensor. The way this affects you is that since the sensor only sees the about 75% of the image produced, the image seems to be more zoomed in than if the same lens was on a FX camera.
Here is a picture showing what a DX and FX sensor would see with a FX lens.
A full frame sensor would see all of the image produced by the lens.
Since the DX sensor is smaller, the image seems more zoomed in.
Here is everything laid on top of each other (just to confuse you)
Pretty much, if you use a DX lens on FX sensor, the lens doesn’t make a big enough image so the corners will be black because there is no image there.
If you use a FX lens on a DX camera, the image will definitely cover the frame. You won’t even be able to tell the lens is a FX lens while looking through the view finder. BUT a 50mm FX lens will look like a 75mm lens because of the “crop factor.” This means the image produced by the FX lens is cropped by the DX sensor. This is useful sometimes because that means a 300mm FX lens on a DX camera looks like a 450mm lens. More zoooooom :)
With Nikon's new V1 and J1 mirrorless camera, there is a new sensor size in the Nikon Market. This sensor is almost 3 times smaller than a full frame camera, 2.7 times to be exact. What that means for you is if you have the new Nikon V1 or J1 with the F mount adapter, your 50mm FX lens will be almost a 150mm!!