Question regarding DX lenses

[vedran]

If a lense is stated as DX lense, does it mean for example that 50 mm is still 50 mm on DX camera or is it refernce to FX sensor format, therefore about 75mm on DX camera. I was wondering because essentialy i want a 50 mm lense, but would a 35mm prime (nikkor af-s) give me the same angle as 50 mm on FX? So would there be any noticeable difference between those two lenses: 35mm on DX and 50mm on FX ? I'm guessing the 35 mm on DX would be worse because it's "fake" magnification due to smaller sensor. Any thoughts? Ty.

 

[snowbear]

The focal length does not change, ever. A 50mm is a 50mm on any camera.

What does change is the field of view. A 50mm will have the same field of view on a DX as what a 75mm will have on a FX, so yes, the angle is different. The apparent size of objects will be the same.

There are many, many threads on this.

 

[Derrel]

Focal length is ALWAYS the same. The now-older "cheap" 35mm f/1.8 DX Nikkor 35mm lens is the same, exact 35mm focal length as the older 35mm f /2 AF-D Nikkor is, and is also the same focal length as the VERY-NEWEST 35mm f/1.8 G-series lens (the one for full-frame Nikons) is.

What **is** different is the coverage circle the 35mm lenses project: the DX-Nikkor lens produces or "projects out the rear element" smaller-diameter circular image than the two other Nikkor lenses project.

Again, for a given lens length, the focal length is always the same on a DX lens as it is on a lens designed for full-format Nikons. What differs is the diameter of the image circle the lenses project: the DX Nikkors can get by with a smaller-diameter image circle because the DX format is so much smaller. A DX-Nikkor only needs to project a roughly 29mm diameter circle in order to cover a DX-format sensor's area; a lens for FX needs a 43mm diameter circle to cover the full FX area which is very close to 24x36mm in size.

 

[astroNikon]

DX lenses are also built with less glass as it does not have to project a large image for the field of view of a larger sensor.
Thus DX lenses are often less costly and smaller in size than a FX lens, from the few I've compared.
With it being less costly, it allows a lower entry level cost and better support lower cost entry level DX packages.

but a 50 is a 50

 

[vedran]

I get it, the dx has smaller sensor area, therefore smaller in diameter. But what i was thinking...if i buy myself a 35mm lense for fx, it would give me the same field of view as 50mm (which is what i want) non-dx lense on fx cam. And once i get myself a camera with a full frame sensor i will still have a nice 35 mm lense for it

 

[astroNikon]

I get it, the dx has smaller sensor area, therefore smaller in diameter. But what i was thinking...if i buy myself a 35mm lense for fx, it would give me the same field of view as 50mm (which is what i want) non-dx lense on fx cam. And once i get myself a camera with a full frame sensor i will still have a nice 35 mm lense for it

yes

When I bought my d7000 I bought all FX lenses except the one kit 18-105 lens. So when I went to FX I was all set. But before the FX everything had the FOV variance.

A lens is a lens, it's the sensor that changes the FOV. THe image on a FX doesn't change it's just taht the DX sensor is smaller and only captures a smaller part of the total image.

 

[snowbear]

Yes, that is correct. Like mt brotha Astro, I only have one DX lens, the 55-200 kit. My other 8 are FX.

 

[KmH]

I get it, the dx has smaller sensor area, therefore smaller in diameter. But what i was thinking...if i buy myself a 35mm lense for fx, it would give me the same field of view as 50mm (which is what i want) non-dx lense on fx cam. And once i get myself a camera with a full frame sensor i will still have a nice 35 mm lense for it

Yes, but. The 35 mm lens will still have the distortion and other characteristics of a 35 mm lens, and not a 52.5 mm lens - 35 mm x the 1.5 crop factor for Nikon Dx image sensors is 52.5 mm, not 50 mm.

 

[Ido]

I get it, the dx has smaller sensor area, therefore smaller in diameter. But what i was thinking...if i buy myself a 35mm lense for fx, it would give me the same field of view as 50mm (which is what i want) non-dx lense on fx cam. And once i get myself a camera with a full frame sensor i will still have a nice 35 mm lense for it

Keep in mind that it probably won't be a nice 35mm lens, at least not out to the corners. As it only needs to cover a DX sensor, putting it in front of an FX sensor will result in some areas in the corners and edges that are darker than the rest of the image, maybe even pitch black, simply because the optics don't cover it. It will also be far softer around the edges.

That's all in theory, though. I suppose there are DX lenses that actually do cover an FX sensor almost in its entirety. One of the reasons Nikon would do that is to avoid vignetting on the DX camera. I've heard the DX 35mm f/1.8 G can cover almost the full FX sensor in a certain range of apertures - not wide open and not fully closed down, but somewhere in between.