Nikon DSLRs come in two formats: the FX-format and DX-format. This refers to the size of the image sensor in the DSLR.
FX-format DSLRs have a sensor size that measures approximately 36 x 24mm, which is roughly the same size as 35mm film. It is also most commonly referred to as ‘full-frame’. DX-format DSLRs comes with a sensor size that measures approximately 24 x 16mm, sometimes referred to as ‘APS-C’.
While both formats deliver superb image quality, the difference in sensor size will affect your photography in different ways.
The FX-format image sensor allows you to capture images with higher sensitivity levels and lower noise, even in low-light conditions. With the shallower depth of field obtained with this sensor size, you will be able to photograph your subjects with beautiful bokeh.
The DX-format image sensor has a 1.5x crop factor, which provides a closer view of your subjects. For example, if you mount a 50mm lens on a DX-format DSLR, you will be shooting with a focal length of 75mm. Due to the smaller sensor, DX-format DSLRs are generally more lightweight and compact.
Whether you choose a powerful FX-format DSLR, such as the D750 or a lightweight DX-format DSLR like the D5500, both will deliver crisp, clear images with incredible detail.