The FX lenses work fine, so I wonder if there is any point buying a DX
Yes there are several points. Because the image circle for a DX is smaller there exist DX lenses which doesn't have counterparts in FX lineup.
Just two examples:
- the famous Sigma 18-35mm f/1.8 DC HSM (no Full Frame zoom with f/1.8 exist)
- the new super-super-zoom Tamron 16-300MM F/3.5-6.3 Di II VC PZD (an equivalent of approx. 25-456mm (!) on Full Frame). And this beast includes also image stabilizer.
Also DX lenses are smaller, easier and cheaper (for example Sigma 8-16mm costs $650 whereas the FX brother - Sigma 12-24mm - costs $950).
However, generally I do recommend you to use FX lenses. Usually (not always, but generally speaking) they are better optically on DX sensors and allow you to upgrade to a Full Frame (FX) sensor in future.
Would a 50mm DX on DX give me the same field of vision as a 50mm FX on
FX at the same magnification?
- Please ask just one question per question. :) Thank you.
- No. 50mm is 50mm. The focal length is a property of the lens. It has nothing to do with the dimensions of the sensor on which the 'field of vision' (as you say) is formed. The 'field of vision' depends on the relationship between the focal length and the dimensions of sensor (given that the sensors are at the same distance from lens). That's why we have focal length Full Frame equivalences. For these equivalences, see a calculator here.
my 50mm FX Lens is like a ~35mm Lens in terms of visible space
IIUC, No (again). Because your sensor is a crop one, the lens will be 'longer' (narrower/"cropped" field of view) not 'wider'. Your 50mm lens will be 50 x 1.52 (the common Nikon crop factor) = 76mm = short tele.