Prime lenses are lighter, smaller, sharper and have better low light capabilities. Prime lenses also force you to consider composition. You can’t just zoom to get close. You have to walk or ride to the optimal vantage point. With a DX Nikon, I would buy either a 18-200 or 18-300 as a walk around lens and a Nikon 35mm 1.8 prime lens for low light and portraits. If you like micro photography, a 105 mm 2.8 lens is great for DX cameras. Some people say to just bump up the ISO and don’t worry about fast glass, but with lower cost DX cameras high ISO shots in low light generate a lot of noise.

I also had questions like this, so I took my "ordinary, cheap, kit" 18-55 lens that came on my D5100 out and took some shots of some grass and dandelions in my back yard at the same aperture and distance as my 55 Micro-Nikkor prime. The shots with each lens were indistinguishable from each other. You don't need to make any excuses for your 18-55; it is sharp, has excellent color, and is far more versatile than any prime. Don't obsess over chart data, just concentrate on your own technique. The 35-cropped-in-to-55 scenario sounds arduous and tacky. The only reason for the 35 to be used would be for the wider aperture in low-light situations, not any perceived "sharpness" issues.

Prime lenses are "usually" intended for full frame cameras, though there are a few exceptions like the 35mm F1.8, the 40mm Micro and the 85mm Micro. The primes are all very good. DX-only zoom lenses make up the rest of the lens offerings for DX cameras, and they range from very good to "meh".

But if you really want to compare, set the zoom to 35mm, or get a 50mm prime to use to compare the zoom at 50mm. When you crop an image you reduce the number of pixels, which results in an image of lower resolution. In most cases, the uncropped 18-55 images will be better than a cropped 50mm.

As far as a prime lens always being better than a zoom lens - you really need to carefully compare lenses at the same focal lengths and apertures - and you may find that there is not a lot of difference at F8 - there is no categorically better lens.

I shoot full frame cameras and have a collection of carefully selected prime and zoom lenses that have similar resolution and contrast, so that in most cases it's impossible to tell the difference at the same focal length and aperture.

Zooms seem to have a reputation that started with the early film era zooms, like the Nikkor 43-86 F3.5 lens which was simply awful. Almost as bad was the 18mm F2.8 prime, and the 300mm F4.5 prime all beautifully built but optically junk. Other poorly designed offerings from Vivitar, Soligor, Kiron and others didn't help much.

Prime lenses are "usually" intended for full frame cameras, though there are a few exceptions like the 35mm F1.8, the 40mm Micro and the 85mm Micro. The primes are all very good. DX-only zoom lenses make up the rest of the lens offerings for DX cameras, and they range from very good to "meh".

But if you really want to compare, set the zoom to 35mm, or get a 50mm prime to use to compare the zoom at 50mm. When you crop an image you reduce the number of pixels, which results in an image of lower resolution. In most cases, the uncropped 18-55 images will be better than a cropped 50mm.

As far as a prime lens always being better than a zoom lens - you really need to carefully compare lenses at the same focal lengths and apertures - and you may find that there is not a lot of difference at F8 - there is no categorically better lens.

I shoot full frame cameras and have a collection of carefully selected prime and zoom lenses that have similar resolution and contrast, so that in most cases it's impossible to tell the difference at the same focal length and aperture.

Zooms seem to have a reputation that started with the early film era zooms, like the Nikkor 43-86 F3.5 lens which was simply awful. Almost as bad was the 18mm F2.8 prime, and the 300mm F4.5 prime all beautifully built but optically junk. Other poorly designed offerings from Vivitar, Soligor, Kiron and others didn't help much.

I have a Nikon D3400 with the two kit lenses. I also have a Nikon D80 I purchased from a member and still trying to learn that one (a bigger challenge). I generally use my 18-55mm lens on the D3400 for most of my shots. It covers the range most of the time. So my question is to the quality of a shot when using the zoom at 55mm or a prime 35mm lens. Aside from sharpness (based on what I think I've learned here), can the 35mm shot be cropped to equal what the 55mm got. Basically enlarging the 35mm shot to equal the 55mm. Do I end up with something just as good or better. Like many here, depending on the situation, I don't want to carry to much if possible. Sometime I can take everything. Hope I explained this properly. Thanks to this site, I kept my camera in manual mode yesterday for every shot for the first time (about 40) and overall did well. Need more practice, but I'm finally comfortable with manual mode.