Nikon DX and FX help, D5100?

I'm currently shooting with a d5100, and was wanting to buy the 35mm f/1.8G but was wondering how what was the whole dx and fx thing. I have a 18-55mm FX kit lens and was wondering if the 35mm on the kit lens was the same view as the 35mm 1.8G. Like zoom wise not focal lenght.i've been told its more around the same as the view as 50 on the kit lens.someone please help.

Any lens you use on your D5100 is going to be affected by its 1.5x crop factor. If you set your 18-55mm zoom at 35mm that will be exactly what you'll see using the 35mm f1.8G prime lens. The main advantage of the 35mm f1.8G prime lens is its fast f1.8 aperture which will be useful indoors when you don't want to use the flash.

There's no zoom with the 35mm f1.8G prime lens.

On a 35mm film camera or full-frame DSLR a 50mm lens is considered a "normal" lens since its angle of view approximates that of the human eye. On your D5100 with its 1.5x crop factor a 50mm lens will have the equivalent angle of view of a 75mm lens on a 35mm film camera or full-frame DSLR.

The 35mm f1.8G prime lens on your D5100 with its 1.5x crop factor will have the equivalent angle of view of a 52.5mm lens on a 35mm film camera or full-frame DSLR. So on your D5100 the 35mm lens would be considered a "normal" lens.

Your 18-55mm kit lens is a DX lens. Nikon does not make a FX version of this lens.

However, you should know that the focal length is a measurement from the sensor to the optical center of the lens. And for both Fx and Dx cameras, this is exactly the same measurement for any given lens.

So, if you put a 35mm lens on a Fx camera, it will be a 35mm lens. If you put the lens on a DX camera, it will be a 35mm lens. Nothing changes.

However, since your D5100 is cropped, it is only using the center portion of the lens. This means that the effect is in reality "digital zoom". The result is that the angle of view is smaller. One comparison that is often made is to get the same "view" on a fx body, a lens of a different focal length is needed. Some photographers refer to this as an "effective" focal length.

So if someone tells you a 50mm lens on your body is effectively a 75mm lens - it is not really accurate. What is accurate is that a FX camera would require a 75mm lens to get the same view as a 50mm lens on your Dx camera - "digital zoom" and all.

The reason "effective focal length" is not accurate is because the DoF actually increases when you use a lens on a Dx camera when the DoF should decrease if the focal length increased.

It is far more understandable to think of a Dx camera as having a 1.5x digital zoom (however, without the loss of image quality normally associated with cameras having a digital zoom function). But the notion of digital zoom rather than effective focal length is more accurate.

Having said all of that, the answer to your question is Yes; the 35mm f/1.8G is going to look exactly like the 18-55mm kit lens if the zoom is parked at 35mm.

So, what is the benefit of the 35mm f/1.8G? Lens sharpness and low-light capability.

So where does the information you have been told come from. If you wanted to get the same view of the 35mm lens on a Fx camera, the Fx user would have to use a 50mm lens, due to the "digital zoom" of the Dx camera, which is the result of the cropped sensor.

This may be confusing at first, and even more confusing when the term "effective focal length" is thrown out. Just remember - a 35mm lens is a 35mm lens, whether it is mounted on a Dx or Fx body (notwithstanding vignetting due to using a Dx lens on a Fx camera), and when you use any lens on a Dx camera, you get a "digital zoom" effect of 1.5x, which appears the same as if a 50mm lens were used on a Fx camera.