# FX lens on a DX body



## amber.martin (Jul 23, 2010)

ok, so i had a problem with another photographer a couple days ago and im wanting to run this by you fine people to make sure im not a jerk for telling her shes wrong. I bought a D90 body from a guy my husband works with and with the body he sold me a 24-70mm 2.8 and a 50mm 1.4 for an AMAZING deal. knowing that these were great lenses, (the 24-70 more so when i upgrade to my d700 or d3) i gladly bought them. upon hearing from a friend about my steal, she wrote me telling me that an FX lens on a DX body will drop my mps from 12.5 to 5. Concerned that i made a bad choise i did my own research and on rockwell's site he said that all a dx body loses on a FX lens is the field of view, and that what she told me was quite opposite, that a DX lens on an FX body drops the mps.. well it seems ive made her upset by doubting, i just want to make sure im correct, kind of a thrid party safety net  thanks in advance


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## Gaerek (Jul 23, 2010)

amber.martin said:


> ok, so i had a problem with another photographer a couple days ago and im wanting to run this by you fine people to make sure im not a jerk for telling her shes wrong. I bought a D90 body from a guy my husband works with and with the body he sold me a 24-70mm 2.8 and a 50mm 1.4 for an AMAZING deal. knowing that these were great lenses, (the 24-70 more so when i upgrade to my d700 or d3) i gladly bought them. upon hearing from a friend about my steal, she wrote me telling me that an FX lens on a DX body will drop my mps from 12.5 to 5. Concerned that i made a bad choise i did my own research and on rockwell's site he said that all a dx body loses on a FX lens is the field of view, and that what she told me was quite opposite, that a DX lens on an FX body drops the mps.. well it seems ive made her upset by doubting, i just want to make sure im correct, kind of a thrid party safety net  thanks in advance



She's totally wrong.

You can use an FX lens on a DX body with absolutely no penalty whatsoever. Most (I believe) FX bodies will internally "crop" the sensor if a DX lens is used with it, so it is not usually recommended. Feel free to use the FX lens on your D90.

EDIT: And about the field of view thing. All lenses are measured in mm. There is no conversion done between DX and FX lenses. A DX lens and an FX lens that are the same focal length will show you exactly the same thing on a DX body. It's only when you put that FX lens on the FX body will the field of view appear different to you. There is no penalty to using an FX body on a DX body, even with regards to field of view.


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## amber.martin (Jul 23, 2010)

yay! lol, i thought so but i guess i needed the reassurance! thanks gaerek!


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## Derrel (Jul 23, 2010)

Yes, she is totally wrong. She's got things confused. I'm extremely familiar with Nikon cameras and lenses, and what that woman told you is just flat-out incorrect.

She's confusing things quite badly! 

There really is no such thing as an "FX lens"...that's a misnomer...there is not a single, not one single Nikkor lens labeled "FX". Out of over 50 million. There are however a small handful of DX Nikkor lenses, which are all labeled DX Nikkor. I'd estimate about 99% of all lenses in F-mount, made by Nikon and others, are normal, 43mm image circle, regular lenses, capable of covering 24x36mm film or digital camera sensors of the full frame size, as well as smaller format digital sensors.

There is NO SUCH THING as an "FX lens" in the Nikon system--there are only DX lenses, which can be mounted onto FX bodies. There are only four Nikon bodies that carry the label FX,and they are the D3, D700, and D3s, and D3x digital bodies. They will accept DX lenses, and will automatically default to a reduced-megapixel capture size, which will cut the MP size and area of the captured area down--to what the DX lens can cover fully!!!

Anyway...not to sound like I am lecturing...it's just that there is no such thing as an FX Nikkor lens..only DX lenses exist, and a D90 is a crop-body camera...and your photographer friend is sadly mistaken. She has no idea what she's spewing.


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## amber.martin (Jul 23, 2010)

good to know! i thought it all sounded off, ive been around cameras a while now and im the first to admit i still have ALOT to learn and that was extemely helpful! but yeah, i thought it sounded like crap, haha my husband claims shes only upset that i got the 24-70 for 100 bucks! i figured i could use it on the d90 and then it will work well on my ff when i get the money saved up!


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## bigboi3 (Jul 23, 2010)

WOW.. 24-70 f/2.8 for $100!!?? Jealous I AM.  I don't have any other inputs other than that because everyone else who posted is correct.


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## amber.martin (Jul 23, 2010)

haha! yeah, i looked on ebay to see what they were going for and I JUMPED on it! no way i could walk away from that!


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## Dwig (Jul 24, 2010)

amber.martin said:


> ...she wrote me telling me that an FX lens on a DX body will drop my mps from 12.5 to 5. ...



Saying that she is totally wrong doesn't quite describe her error correctly. There was a seed of very correct information floating around in her thoughts. Its just that she got hold of the wrong end and looked down the path of logic the wrong direction.

By default, when a DX lens is mounted on an FX body, the body shifts to a crop mode using a smaller portion of the sensor, emulating the smaller DX sensor. This results in a lower pixel count in the resulting image but the image doesn't suffer from vignetting or other quality loss around the edges. Your friend confused this "DX lens on FX body" with your use of lenses capable of covering an FX sensor (slang="FX lens", though Nikon never uses this term) on a DX body. 

Nikon uses DX and FX as labels on their bodies. Curiously, they use DX on the lenses that only cover the smaller DX format, but don't actually use the FX term for lenses capable of covering the larger full frame format. They leave these lenses without a designation specifying coverage. It is somewhat common user slang to reduce "lens capable of covering an FX sensor" to "FX lens".


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