FX & DX Lenses on DX Body

Question

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....

I take a picture with a 50mm FX prime on a FX body
I take a picture with a 50mm FX prime on a DX body
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?

Sorry, that possible duplicate is the opposite. But there are other existing questions which cover this.... — mattdm, Nov 25 '17 at 06:41
Perhaps this one? https://photo.stackexchange.com/questions/38899/why-do-full-frame-lenses-and-crop-body-lenses-exhibit-the-same-crop-factor-when — mattdm, Nov 25 '17 at 06:44
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! — tryan, Nov 25 '17 at 06:56
@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. — Michael C, Nov 25 '17 at 08:04
Related: Why do my 50mm APS-C and 50mm FF lenses have the same angle-of-view on my APS-C camera? The only answer to that question (also marked as a duplicate) has links to 13 other questions here among the near countless examples that ask the same thing here. — Michael C, Nov 25 '17 at 08:08
I think maybe Does my crop sensor camera actually turn my lenses into a longer focal length? covers this most closely. — mattdm, Nov 25 '17 at 17:14

mattdm · Accepted Answer · 2017-11-25T17:17:38.937

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:

Dozens? Don'tcha' mean hundreds? – Michael C Dec 23 '17 at 12:50 — Michael C, Dec 23 '17 at 12:50

FX & DX Lenses on DX Body

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