DX vs FX

[Poider]

G'day just wondering what affect using a FX lens on a DX body has, I am aware that an FX lens is for a full frame sensor and a DX is fro a cropped sensor, what does a FX lens do or not do on a DX body?
Is the only difference the full frame? does the auto focus still work on a DX body?
Is there a reason why I wouldn't want to use an FX lens on a DX body?
Peter

[ravncat]

The only real difference is the size of the image circle made by the lens. An FX lens makes an image circle big enough to cover an FX sensor, a DX lens does not. Because the FX image circle is bigger it covers the DX sensor just fine...

So, an FX lens on a DX body, works just fine. A 35mm dx and 35mm fx lens on your camera, will give you the same field of view.

There are a few small differences- equivalent FX lenses tend to be larger than DX lenses. A DX camera will really only "use" the center part of the FX lens - the center part is usually sharper.

As for Autofocus, in Nikonland - that depends a bit on your camera body. All you have to worry about is whether the lens is Af-S or not. So the 35mm f2 AF-D full frame lens will not autofocus on your camera, but the 70-200 F2.8 AF-S full frame lens will focus on your camera.

No real reason not to use an FX lens on a DX body - other than they tend to cost and weigh more...

[OsmosisStudios]

There are no limitations of using a FX lens on a DX body other that you have the crop factor (though that is true for anything used on a DX body).

[Poider]

ok thank you both

[sk66]

To add to it, often you get better performance from an FX lens on a DX body. That's because the worst parts of an image are usually the perimeter and the DX sensor crops that off. So a FX lens which is characterized as "soft in the corners" may not have that problem on your camera.

[Poider]

ok thnx I will have to look at that when I eventually get to buy more lenses