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I have a set of FX Lenses for my 35mm SLR, but also a DX Digital SLR. The FX lenses work fine, so I wonder if there is any point buying a DX Lens?

The DX camera was body-only, and I'm currently using a Nikkor 50mm f/1.8D AF, hence I'm not sure what difference a real DX Lens would make?

There are several questions regarding DX-Lens on FX/35mm-Body, but only a few about FX-Lens on DX-Body, where the consensus is that the field of view is narrower - my 50mm FX Lens is like a ~35mm Lens in terms of visible space, but not in terms of magnification. That's how it looks when I compare the same lens through my Film-SLR: It's the same distance/magnification, just less in the picture.

Is that the only difference? Would a 50mm DX on DX give me the same field of vision as a 50mm FX on FX at the same magnification?

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Michael Stum
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  • @Hugo I'm not sure if it's really the same. In my case the question is more about "I already have FX Lenses, is there any reason to go for a DX", while the answered question is more about "I have no Lenses, should I buy DX or FX" and doesn't really answer what's wrong apart from Price and Size. – Michael Stum Jul 16 '14 at 06:08
  • They are not exactly the same, but very similar indeed. Look at the top answer to the other question: http://photo.stackexchange.com/a/844/21986 "The price you pay for using FX lenses on DX is bigger and heavier lenses and less appropriate focal lengths." I think that answers your question. In what way do the existing answers fall short regarding your question? – Hugo Jul 16 '14 at 06:14
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    The last part, about field of view, is unequivocally answered. I don't think we need to go through that again. And for FX lenses on DX bodies in general, the question I linked above may help. – mattdm Jul 16 '14 at 06:27
  • @MichaelStum A 50mm lens on a DX body yields the same FoV as a 75mm lens on an FX body. You've got the conversion factor backwards in your question. – Michael C Jul 16 '14 at 12:04

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The FX lenses work fine, so I wonder if there is any point buying a DX Lens?

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?

  1. Please ask just one question per question. :) Thank you.
  2. 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.

John Thomas
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