which means that a DX sensor image will be about 50% larger than
the 35mm traditional film.
And FX (full-frame) sensors are the size of an actual 35mm movie
frame (36x24mm) and about twice the size of the DX sensor. So
which do I need and why?
Although there are advantages and disadvantages to both DX and
FX, most of us would prefer to have FX sensors over DX for several
reasons, although both work fine for many purposes. Here are
some reasons:
More on Sensor Size
The FX (full-frame, FF) sensor, being physically larger, has more
individual pixels, but not necessarily less noise. We have two forces
working against one another here. The larger the individual
photosites (pixels), offer potentially more light (and less noise). If
we are using a 36MP sensor, which is a fixed size (FF), then the
pixels can't be that large, so the camera manufacturer has to find
some way to reduce the noise other than pixel size. The Sony A7s
has a full-frame sensor, but is only 12MP, so I has relatively very
large photosites and therefore is (currently) the ultimate low-light
camera.
DX sensors are smaller. FX is more sensitive to color IMO and also
sharper. FX sensors also have a larger dynamic range than DX and
suffer less from lens diffraction so I am told. And last, the smaller
viewfinders on DX cameras mean they are not quite as bright as
with FX. As a macro shooter, I need a bright viewfinder that lets in
lots of light.
In addition FX is compatible with DX cameras, but not vice versa. In
other words, you can use all your FX lenses on the smaller DX
sensors but not the other way around. Keep in mind that any lens
we use on a DX camera will be 50% longer in reach (mm) than if it
is used on an FX camera. For example, place a 100mm lens on a
DX body and that lens has a reach of 1.5x (150mm) and so on.
Some DX users like this because a 200mm telephoto lens is
suddenly a 300m lens. DX lenses are also less expensive, less
heavy, and so on. Still, while I have them, I don’t use DX them...
much.
That being said, the smart money folks are buying FX lenses
because they work on both sensor types AND they are a hedge