Etikettarkiv: projection

The Difference Between DX and FX Lenses

Sometimes people ask questions on what the difference is between DX and FX lenses. DX and FX are Nikon lingo in specifying different sensor sizes on cameras.

On digital cameras Nikon have traditionally employed what they call DX size sensors. This sensor was originally a CCD type sensor such as the one in the D70 camera and has later been replaced by a CMOS sensor on the later versions such as D200 and later cameras.

Before we all went digital a ”normal” prosumer or semi-pro camera was almost always a 135 system camera. This means we had 35 mm film in the camera and the projected image was usually 24×36 mm onto this film. With the invention of the APS-C format sensor which is 23.7 x 15.5 mm in size this format was known as DX. They are all small format cameras.

Because the digital bodies, with the exception of the so called ”full frame” bodies, have a much smaller area onto where to project the image from the lens, it is possible to make cheaper and lighter lenses by sacrificing the area outside the sensor. The result is a special line of lenses called ”DX” lenses.

Canon, Sigma, Tamron, Tokina… they all have their own respective way of denoting lenses that are ”optimized” for digital DX format cameras. But what happens if you mount a DX lens on to an FX body and start taking pictures?

In the worst case you would get completely black corners. Because the ”full frame” sensors are bigger parts of them may fall completely outside the projected image by the sensor, something that would lead to black corners.

In many cases it would not be so dramatic but instead you would see some vignetting, the falloff in light in the corners and in all cases you can be pretty certain that sharpness, chromatic aberration and so on will not be very good in the corners of the picture.

Here is a demonstration of the difference and why it may be difficult to use DX lenses onto the new types of digital cameras with larger sensors, results will vary depending on the actual lens, some DX lenses work better but never as well as a lens actually designed for FX format cameras.

This picture shows an extreme case of vignetting where the image from the lens fails to cover the whole sensor of the camera. This can happen for example with extre wide-angle lenses designed for DX cameras and mounted onto FX bodies.
This is a more normal result of what most DX lenses would produce on FX bodied cameras, the falloff is more graduated and could still be useful.
Here is the lens used on a DX format camera. Note how the crop factor of the camera "crops away" all the vignetting of the lens.

By not having to design lenses for the full FX format the manufacturers can make do with smaller lenses, this means they can be lighter (good for hiking photography) and they can be made cheaper.

How about using FX lenses onto DX cameras then?

That works exceptionally well! Because of the crop factor the DX body will use only the best part of the lens, usually the middle of the picture is sharper and more defined than the edges and if the edges are cropped away because of the smaller sensor you will have excellent sharpness all the way out in the corners of the picture!

So there are definitely advantages to the DX type bodies, that should not be forgotten!