I've got a Nikon D3100 with an 18-55mm zoom lens. I'm keen to experiment with some other lenses and a friend of mine recently reccommended I purchase a fixed 50mm f/1.8 lens as he said it's good for portrait photography and capturing really sharp images. He also said that as it isn't a zoom lens it will sharpen my composition skills.

My question is - I currently have an 18-55mm zoom lens, so by purchasing a 50mm fixed lens, won't I be purchasing a spec of lens already covered by my 18-55mm lens? What are the main differences between these two lenses?

Finally - can anybody vouch for the Nikon fixed 50mm f/1.8 lens as being a good lens to go for?


5 Answers 5


At 50mm on your 18-55, the max aperture is f/5.6. On the 50mm f/1.8, the max aperture is - obviously - f/1.8. It is perhaps not immediately obvious, but f/1.8 lets in 10-12 times more light than f/5.6. That is the difference between shooting at 1/10 second shutter speed (which is absolutely a no-go for moving subjects) and shooting at 1/100 (which is a usable shutter speed for moving subjects). Big difference indoors at night, for example. It lets you shoot without flash, or with the flash used as mere fill flash instead of it being the main light-source.

Note that Nikon has two variants of the 50/1.8, one with a built-in autofocus motor and an older one without. Do get the new one.



  1. You'll get f/1.8 @50mm which is much useful in low light conditions.
  2. Your images will be slightly sharper than usual. Specially if you shoot around f/2.8.
  3. You'll get shallower DOF which will get significantly better background blur and subject isolation.
  4. You will get the taste of walking zoom method :)


  1. It will not AF in your Nikon D3100 body.
  2. You will lose zoom flexibility and will surely miss wide angle.
  3. You'll need to switch between your lenses often.
  • 3
    \$\begingroup\$ 3. Decreased depth of field, not increased! \$\endgroup\$
    – Staale S
    Commented Oct 15, 2011 at 8:51
  • \$\begingroup\$ I have the Nikkor 50mm f1.8 AF-S SWM (Silent-Wave-Motor) which has autofocus for my D5000 which is, just like D3100, without in-body focus motor. \$\endgroup\$ Commented Oct 15, 2011 at 9:41
  • \$\begingroup\$ @Andrei Rinea: I have not heard about that model before. Theres a 50mm f/1.8 G for Nikon DX which will AF with D3100 but not the typical 50mm f/1.8. Any link to the product you're talking about? \$\endgroup\$ Commented Oct 15, 2011 at 14:36
  • \$\begingroup\$ @ShutterBug I believe that you and Andrei are thinking of the same lens -- the 50mm f/1.8G AF-S. It's not DX only, though: its image circle covers a full 36x24mm sensor. \$\endgroup\$
    – Evan Krall
    Commented Oct 15, 2011 at 20:20
  • \$\begingroup\$ I have bought the lens from this exact site page : f64.ro/products/description/Nikon_50mm_f_1_8_AF_S/index.html \$\endgroup\$ Commented Oct 15, 2011 at 20:48

The advantage is that kit lenses are usually poor, and prime lenses rock.

Now seriously, I can tell you about my experience with the Samsung GX-10 kit 18-55mm f3.5-5.6 lenses (and at least its Pentax K10D counterpart was reviewed as better than equivalent Nikon and Canon kit lenses, I do not know if they were much more different than its twin camera) vs Pentax KA 50mm f1.7.

The 50mm f1.7 produces images that are sharper, with more contrast, more vivid colours, almost zero geometric and chromatic aberrations, less vignetting, and an incredibly narrow depth of field if needed.

And your friend is quite right, having a fixed length lenses pushes your creativity further because you do not have to care about choosing a focal length (and can focus on other important things) and you will need to move around the scene to get the best framing, possibly noticing things that with a zoom lenses you would have missed.


To add to Shutterbug's answer, it might be worth looking at the new Nikon 40mm f2.8 Macro. On a crop sensor like your D3100's it is still just long enough for portrait work, and the f2.8 aperture will still blur the background nicely, but you also gain a true macro lens into the bargain, and you don't lose autofocus like you would with the 50.

  • \$\begingroup\$ I do have the 40mm Micro Nikkor 2.8. It's quite nice for non-macro work such as portraits! \$\endgroup\$ Commented Oct 15, 2011 at 9:40

50mm f1.8g is the a big bang for the buck. It will provide way more perceptual megapixels when you shoot, Hence capturing far more detail. It will let you blur the background and will have better low light capability as lower f-stops let in more and more light.

But beware that zooming in and out will require legwork and it might get difficult to get pictures in cramped up places. but as you have a 18-55mm lens anyhow so that is hardly going to be a problem for you.

  • \$\begingroup\$ "perceptual megapixels" is not a standard photography term; it is a term made up by DxOMark, to try to reduce the optical performance of lenses, which is described by MTF curves, to a simple easy-to-compare number. \$\endgroup\$
    – scottbb
    Commented Aug 9, 2017 at 14:50

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