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If I use a 50mm prime FX lens on a FX camera, I will get 50mm. If I use a 50mm prime FX lens on a DX camera, I'll get 75mm (assuming 1.5x crop factor).

Now, if I use a 50mm prime DX lens on a DX camera, do I get 50mm or 75mm? In other words, does a 50mm prime DX lens already account for the crop factor? Does the multiple only exist for a FX lens on a DX camera?

Note that I'm asking about putting FX and DX lenses on a DX body - not putting them on a FX body. I read this article but it discusses putting DX lenses on an FX body. I just want to know if 50mm is 50mm whether it's DX or FX lens; and if I put that on a FX body it'll be 50mm and DX body it'll be 75mm.

To further clarify....

  1. I take a picture with a 50mm FX prime on a FX body
  2. I take a picture with a 50mm FX prime on a DX body
  3. I take a picture with a 50mm DX prime on a DX body

Photos 1 and 2 will be different - 2 will be zoomed by 1.5x. Will 1 and 3 be the same or will 2 and 3 be the same?

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  • \$\begingroup\$ Sorry, that possible duplicate is the opposite. But there are other existing questions which cover this.... \$\endgroup\$
    – mattdm
    Commented Nov 25, 2017 at 6:41
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    \$\begingroup\$ Perhaps this one? photo.stackexchange.com/questions/38899/… \$\endgroup\$
    – mattdm
    Commented Nov 25, 2017 at 6:44
  • \$\begingroup\$ Kind of mattdm, but not quite.. I couldn't find a clear answer in that thread differentiating between FX and DX lenses even though there was a thorough discussion of crop factor calcs. Thanks for sharing! \$\endgroup\$
    – tryan
    Commented Nov 25, 2017 at 6:56
  • \$\begingroup\$ @tryan 50mm is 50mm. On a 1.5X crop body a 50mm lens will give an ≈23° diagonal angle of view. It doesn't matter if it is a DX or FX lens when you are using a DX body. \$\endgroup\$
    – Michael C
    Commented Nov 25, 2017 at 8:04
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    \$\begingroup\$ Here's a link to 31 questions on the same subject. \$\endgroup\$
    – Michael C
    Commented Nov 25, 2017 at 8:11

1 Answer 1

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Lenses are labeled with their actual focal length. The concept of "equivalence" or "crop factor" only exists to help compare between different formats. For your examples, only example 1 has a wider field of view. The DX camera doesn't care that the lens happens to have a bigger image circle.

We have literally dozens of questions along these lines. Some of the most helpful in your particular case are:

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  • \$\begingroup\$ Dozens? Don'tcha' mean hundreds? \$\endgroup\$
    – Michael C
    Commented Dec 23, 2017 at 12:50

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