Nikkor 50mm f/1.8 AF-D FX Review

This article will concentrate on the Nikkor 50mm f/1.8 AF-D MTF50 resolution performance and discuss how well the lens autofocuses. Repetition of the published Nikon specifications of the lens will be mostly avoided.

This is one of the most popular Nikkor FX “prime” lenses ever produced, known as the “nifty fifty” (the 50mm f/1.4 shares this title, but the price of the 1.8 makes it much niftier). It’s also one of the most inexpensive Nikkor lenses. I’ve paid more for filters than I did for this lens. This is another of the Nikkor lenses that falls into the category of “just get one”. It’s reasonably fast, focuses well, and is one of the tiniest lenses Nikon has made. It has been superseded by the “G” version, which loses the aperture ring.

When used on DX cameras, this is a particularly good focal length for portraits (75mm equivalent).

What you don’t get: vibration reduction and great corner resolution when the aperture is wide open.

My usual disclaimer: this is looking at a single copy of the lens. Yours will be different, but hopefully ‘similar’. The only place I know of that tests lots of copies of lenses is here. I was lent another copy of this lens (not being reviewed here) and it was NOT good. You need to verify your own copy; I don’t believe that Nikon tests each lens, or else the other copy I was lent wouldn’t ever have made it out of the factory.

These tests were done using a Nikon D7100 (24 MP) with unsharpened 14-bit compressed RAW format. Given this fact, I’m not reporting on the edge performance of an FX sensor.

Here is a link to get pretty good information on this lens. My main complaint with them (and most of the other web sites) is that they simplify resolution measurement down to a single number for an f/stop. It’s not that simple; resolution is a 2-dimensional thing (not to mention sagittal/meridional directions within those 2 dimensions).

The focus ring on this lens is a wide-enough one, nearest the filter. Being a “D” lens, you can’t just use it anytime you want to override autofocus; you need to set your camera into manual focus mode first. Note: keep your hands off the lens during auto-focus; the focus ring will spin around! I’m guilty of virtually never overriding auto-focus on a short lens like this, so manual focus considerations are a “don’t care” for me on this lens unless I’m shooting infrared.

The lens also has a proper metal lens mount, but no gasket (rubber seal). There’s no dust/weather resistance.

There is a distance scale. Comes in very handy for infrared when I can’t see the subject through the viewfinder.

Also note: DO use this lens for infrared! I use it with the Hoya R72 52mm IR filter. There is no “hot spot” in infrared that often happens with lenses, so it works fine for that purpose (in manual focus mode, of course).

Nikkor 50mm f/1.8 AF-D FX with 52mm filter. Tiny lens!

Autofocus

Only works on cameras with the built-in “screw drive” focus motor. If your camera doesn’t have the screw drive, then you will need the more expensive “G” version of the 50mm. All of my lenses need some focus fine-tune calibration; so does this lens. The focus speed is largely controlled by which camera is attached. I haven’t seen repeatability issues on either my D7000 or D7100, and the focus speed has been more than enough.

Vibration Reduction (VR)

Nope. Helps keep this lens inexpensive. Even Nikon’s 85mm f/1.4 AF-S doesn’t have VR. Just saying. I wish all my lenses had VR, but such is life.

MTF50 Resolution Testing

This is why you should read this article. I will provide the information to enable you to evaluate resolution between lenses in a standard, scientific way yourself, if you wish to double-check me. Also, since your lens results will be different than mine, the following results are just a guideline. See my MTF Cliff’s Notes article to be able to repeat these tests for yourself.

Resolution measurements are in MTF50 lp/mm. This measurement represents how many image line pairs can fit inside a millimeter before the white-to-black chart transitions degrade to 50%; e.g. “turn to mush”. For me, anything beyond about 30 lp/mm is fine, and beyond 50 is outstanding. Higher-resolution sensors yield higher measurements, much like you’d expect.

Before I forget, you will notice a couple of weird blobs in some of the resolution plots that follow. Please ignore these, since they are definitely not a lens imperfection. The measurement software is extremely sensitive, and an imperceptible chart surface indentation shows up very clearly in the measurements. The real resolution reference is the annotated photograph of the resolution chart, which shows each little square’s edge in “cycles per pixel” units.

I use a (free!) program called MTF Mapper from here to measure lens resolution. The download site also has files for printing out the resolution targets (mine are A0 size on heavy glossy paper (‘satin’ finish seems to work just as well), dry-mounted onto a board). This program is covered in more detail in another article, but suffice it to say that this is really great stuff; it’s comparable to ‘Imatest’ in the quality of the MTF measurements, and it uses the “slanted edge” technology similar to ‘Imatest’, also. The author of MTF Mapper, Frans van den Bergh, really knows his stuff. Visit his site and give him the praise he deserves.

The chart design used for resolution tests orients all of the little black squares to be ‘slanted’ but they’re generally aligned in meridional and sagittal (think spokes on a wheel) directions to correlate better with the usual MTF plots you’re familiar with. There’s often a dramatic difference in sharpness between these two directions, and the chart photographs show it clearly.

The meridional/sagittal differences are what “astigmatism” is all about. This lens is decent in the sagittal direction when you get away from the lens optical center, and corners are “okay”. Meridional direction isn’t as good, but judge for yourself in the ensuing resolution plots.

The middle of the lens is impressive, as you’ll see.

What the resolution target looks like. My target is mounted ‘upside down’.

At long last, I’m getting around to some actual resolution results.

Tests were done with “Live View” AF-S autofocus, contrast detect, IR remote (cell phone, actually), and a really big tripod. That’s how I get around any phase-detect problems with focus calibration. The results don’t seem to improve using manual focus and 100% magnification in Live View, so I don’t bother. I use the “best of 10 shots”; not every shot gets the same resolution results. All cameras operate on the “close enough” principle for focus, so many tests are needed to determine the best resolution that the lens can produce.

Frans van den Bergh has an article on how he tested the Nikon D7000 phase-detect focus accuracy by doing a series of tests starting at minimum focus and then a series of tests starting with the lens focused at infinity. He found a definite correlation showing how the camera stopped focusing once it decided that focus was “good enough”, so the infinity-focus-start series would focus a little behind the target, and the start-at-minimum-focus-distance series would end up with focus a little in front of the target.