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Nikon 20mm f/4
NIKKOR (1974-1978)
© 2013 KenRockwell.com. All rights reserved.

Intro    Specifications    Performance   Compared   Recommendations

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Nikon 20mm f/4

Nikon 20mm f/4 AI (52mm filters, 7.4 oz./209g, about $200 used). enlarge. This free website's biggest source of support is when you use any of these links, especially this direct link to this lens at eBay (see How to Win at eBay) when you get anything. Thanks! Ken.

October 2013   Nikon Reviews   Nikon Lenses    All Reviews

How to Use Ultrawide Lenses

Why fixed lenses take beter pictures

Sharpness Comparison to other 20mm lenses

20mm lens falloff comparison

Zeiss 21mm Comparison


Ideal Uses

Superb FX ultrawide, and ultracompact, too. This 20mm f/4 is Nikon's smallest and lightest ultrawide ever; it's smaller than any 50mm lens!


Not for

I wouldn't bother with this on a DX camera. I'd use any DX lens, like the 18-55mm kit lens, instead. As a manual focus lens, I wouldn't use it for sports, kids or action since it's too hard to track focus by hand.


Ergonomics: (manual focus)


Introduction       top

Intro    Specifications    Performance   Compared   Recommendations

Compatibility    History     Pricing

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The Nikon 20mm f/4 AI is one of my very favorite Nikon lenses of all time. This is because it's super-compact, takes standard 52mm filters, and is optically the same as all of Nikon's bigger 20mm lenses and ultrawide zooms. The only Nikon lenses which can outdo it optically are the 16-35mm VR and the 14-24mm, but they are to big to use in the field.

Galen Rowell loved it, too: he raved about it in the September 1999 issue of "Outdoor Photographer" magazine. Why? Simple: Galen found it optically superior to the 20-35mm f/2.8 AF-D zoom many professionals lugged around, and it's one of the tiniest lenses Nikon has ever made. Size is very important to those of us who actually shoot.

This lens is a little hard to find; Nikon only made it for a few years before it was replaced with the equally excellent 20mm f/3.5.

Here is an article about its development. Its tiny size was quite revolutionary and resulted in patents for its innovative design.


Compatibility       intro     top

The manual-focus Nikon 20mm f/4 works great with most Nikon cameras, 35mm and digital — if it's either the newer AI version, or has been updated to AI. If it's a non-AI version and hasn't been updated, it's called an F-mount or pre-AI lens, and while it works perfectly on every Nikon SLR made up through 1976, will have more limited utility with more recent Nikons.

Presuming yours is AI or AI-updated, the 20mm f/4 works flawlessly with every manual focus Nikon ever made, from the F of 1959 through the FM3a and today's FM-10.

With an AI or AI-updated lens, on the D4, D800, D800E, D600, D610, D3X, D3s, D3, D7100, D7000, D700, D300, D200, D2 and F6, use the "Non-CPU Lens Data" menu option to set 20mm and f/4 to get full color matrix metering, EXIF data and finder read-out of set aperture. It works great in aperture-preferred as well as manual modes on these cameras.

With an AI or AI-updated lens, it works perfectly on every professional 35mm camera (F, F2, F3, F4, F5, F6), and adds Matrix metering on the F6.

If it is a true AI lens, it also adds matrix metering on the F4 and FA. If it has been updated to AI, it doesn't offer matrix with the F4 or FA, which uniquely require real AI lenses for matrix metering — they have an extra lug on the back not added in the later AI update process.

The meters of cheaper digital (D90, D5000 and below) and cheaper 35mm cameras (N80 and below) will not couple (or work at all) with this lens, so you'll be on your own guessing exposure using the rear LCD or an external meter, or get a tiny Gossen Digisix meter and hotshoe adapter to meter manually.

See Nikon Lens Compatibility for details on your camera. If your 20mm f/4 is not AI or updated, read down the "Pre-AI" column, if it's been AI-updated, read down the "AI Converted" column, and if it shipped originally as an AI lens, read down the "AI, AI-s" column.


Nikon 20mm History        intro       top



Nikon repackaged their 2.1cm (21mm) f/4 rangefinder lens, originally designed for the Nikon SP, for the F-mount SLRs.

It required the use of mirror lockup and a separate finder slid over the funky rewind crank of the NIkon F, as it poked all the way into the camera.

Nikon made about 5,000 of the 2.1cm f/4 lenses.



The 20mm f/3.5 UD was Nikon's first 20mm lens. It was the ultrawide for the late 1960s and early 1970s. There was no wider non-fisheye lens made by Nikon until the insane 15mm f/5.6 of 1973 and the 18mm f/4 of 1974.

Nikon made about 40,000 of the 20mm f/3.5 UD lenses.



This tiny 20mm f/4 (52mm filters), the smallest ultrawide ever made by Nikon or Canon, replacing the big 20/3.5 UD, with similar optical performance.

In 1975 Nikon introduced the world's widest non-fisheye lens, the Nikkor 13mm f/5.6, which remains today a the world's widest professional SLR lens ever made.

Nikon made F-mount (non-AI) 20mm f/4s from 1974-1977. The mount was redesigned as an AI lens in 1977, and sold until 1978.

Nikon made about 35,000 of these 20mm f/4 lenses, about half AI and half not. Most non-AI lenses have long since been updated to AI.



Nikon replaced the tiny 20mm f/4 with an almost-as-tiny 20mm f/3.5, which also takes 52mm filters.

Nikon made about 55,000 of the 20mm f/3.5 AI and AI-s lenses.



Nikon replaced the tiny 20mm f/3.5 with today's 20mm f/2.8, which takes 62mm filters and is sold today in both manual-focus AI-s and autofocus versions.

Nikon has made about 70,000 of the 20mm f/2.8 AI-s lenses as of 2010, and still makes them today.

Nikon has made about 115,000 of the 20mm f/2.8 AF and AF-D lenses as of 2010, and still makes them today.


Pricing        intro       top

Price in that era's dollars

* Corrected for inflation, 2010, and at full NYC discount. Very few people bought their lenses this inexpensively back then.


Nikon 20mm f/4

Nikon 20mm f/4 AI. enlarge.


Specifications         top

Intro    Specifications    Performance   Compared   Recommendations



Nikon calls this the Nikon NIKKOR 20mm f/4, and adds "AI" to the newer models.


Optics            top

This tiny jewel has 10 elements in 8 groups.

It doesn't use floating elements, called "CRC," in other lenses.

It's multicoated, which Nikon calls Nikon Integrated Coating.


Angle of View        top

94° on FX and 35mm.

71° on small-format DX.


Diaphragm            top

Nikon 20mm f/4

Nikon 20mm f/4 AI at f/5.6. enlarge.

7 straight blades.

Stops down to f/22.


Aperture Ring            top



Full-stop clicks.


Close Focus            top

1 foot.

0.3 meters.


Maximum Reproduction Ratio            top



Angle of View        top

94° on FX and 35mm.

71° on small-format DX.


Focal Length        top


On a small-format DX camera, this lens sees an angle-of-view similar to what a 30mm lens would see on a full-frame camera.


Hard Infinity Focus Stop?            top


This is great for astronomy; just turn to the stop and you have fixed laboratory-perfect focus all night.


Focus Scale            top

Yes, very precise.


Depth-of-Field Scale            top

Yes, very precise.


Infra-Red Focus Index            top

Yes: red dot in depth-of-field scale next to the f/4 mark.


Filter Thread            top

52mm, metal.

Does not rotate.


Size            top

Nikon specifies 1.4" (35.5mm) extension from flange (1.9" (47.5mm) overall) by 2.5" (63.5mm) diameter.


Weight            top

7.357 oz. (208.6g), measured, AI version.

Nikon specifies 7.4 oz. (210g).


Hood            top

HN-14 screw-in metal hood, optional.

Bizarre HK-3 slip-over metal hood. The HK-3 slips over the focus ring and holds on with a compression fitting!

You can ignore the hood. The filter threads provide about the same degree of stray light protection as the hood. Either tiny hood doesn't improve anything; unlike the 15mm f/3.5 AI-s, this 20/4 thankfully has few ghosts or flare problems, so you luckily just don't need a hood.


Case            top

CL- 31, pouch No. 54, or CP-1 plastic bubble.

All are optional.


Made in            top



Teleconverters            top

TC-200/201 and TC-14A, but why on Earth would you want to carry a separate teleconverter to turn this into a 28mm f/5.6 or a 40mm f/8 lens?


Performance       top

Intro    Specifications    Performance   Compared   Recommendations

Overall   Focus     Color    Distortion    Ergonomics

Falloff    Filters    Ghosts   Color Fringes

Mechanics    Sharpness   Sunstars


Overall      performance     top

The performance of this 20mm f/4 AI is indistinguishable from today's newest 20mm f/2.8 AI-s and 20mm f/2.8 AF-D lenses. This 20/4 is simply one stop slower, and a whole lot smaller.

This 20mm f/4 is the smallest ultrawide lens or zoom ever made by Nikon.

The maximum aperture is really closer to about f/4.5. Don't worry, the metering system compensates for all this. By cheating a little like this Nikon was able to get stellar performance in this tiny lens.


Focus      performance     top

Manual focus is excellent.

It is very precise, not fast. The focus ring turns 140.º The 20/3.5 AI-s is geared for faster focus (the ring only turns 70º) if you prefer it that way.

The D3, D3X, D3s, D700, F4, F5, F6 and most professional AF cameras have three very precise electronic manual focus indicators, with which this lens works perfectly.

Lesser digital cameras, like the D300s and down, usually have just one "OK" focus dot, which is not as precise as two arrows and a dot.


Color Rendition      performance     top

The color rendition of this Nikon 20mm f/4 matches my other multicoated Nikkors.


Distortion      performance     top

The Nikon 20mm f/4 has little distortion. It bloats-out a little in the center, and gets straight again towards the sides.

Vertical lines on either side, about 1/2 to all the way out, stay relatively straight.

Here's an uncorrected FX image of the sea, with the horizon along the top:

Nikon 20mm f/4 distortion

La Jolla Cliffs on FX, uncorrected. enlarge.

If correcting it with simple tools like Photoshop's lens distortion filter, some slight waviness will be left after these corrections. These aren't facts or specifications, they are the results of my research that requires hours of photography and calculations on the resulting data.

If shot on DX, which is silly, you see more distortion because you're only using the center of the image, where distortion is strongest, but much easier to correct.

FX and Film
10' (3m)

© 2010 KenRockwell.com. All rights reserved.

* Some waviness remains.


Ergonomics      performance     top

Nikon 20mm f/4

Nikon 20mm f/4 AI. enlarge.

The Nikon 20mm f/4's ergonomics are perfect.

All it is is a focus ring, a mounting and unmounting grab ring, and an aperture ring.

Newer lenses often lack an aperture ring or a decent focus ring.

The grab ring is especially easy to grab well.


Falloff (darkened corners)          performance     top

Falloff is visible wide-open and at f/4, mostly goes away at f/5.6, and is gone at f/8.

Falloff on FX is exactly the same as Nikon's other 20mm lenses and wide zooms.

See my 20mm lens falloff comparison.

It won't be an issue at all on DX (see crop factor).

I've exaggerated this by shooting a gray field and placing these on a gray background.


Nikon 20mm f/4 AI falloff on FX and film at infinity, no correction.


© 2010 KenRockwell.com. All rights reserved.




Filters, Use with      performance     top

Filters are tight; you have to use a genuine Nikon-brand filter or risk vignetting, since the Nikon filters are thinner.

Don't use a polarizer; they don't work with well with any 20mm lens because the polarization of nature itself varies over such a broad angle.

To use more than one filter at a time, use a 52mm -> 77mm step-up ring, and use 77mm filters.


Flare and Ghosts      performance     top

It has very few magenta ghosts, if you get the disc of the sun in your image.


Lateral Color Fringes      performance     top

There can be some minor blue/yellow lateral color fringes when shot on the D3.

On 35mm, which offers no automatic correction, there are also some small yellow/blue lateral color fringes visible under the microscope.


Mechanics      performance     top

Nikon 20mm f/4

Nikon 20mm f/4 AI. enlarge.

Like all Nikkor manual focus lenses, the Nikon NIKKOR 20mm f/4 is built to the highest mechanical standards. This isn't some made-in-Red-China plastic dog plop.


Barrel Exterior

Anodized and enameled aluminum.


Filter Threads

Anodized aluminum.


Focus Ring

Metal, rubber covered.


Focus Helicoids

Feels like brass: smooth and silky with no play or need for damping grease.


Depth-of-Field Scale

Engraved into barrel and filled with different colors of paint.



All metal.


Aperture Ring

Cast aluminum, anodized and enameled.

Engraved markings filled with different colors of paint coded to the depth-of-field scale.



Dull-chromed brass.



Engraved into the metal and filled with paint.


Identity and Serial Number

On the front of the lens, inside the filter ring, engraved into the metal and filled with paint.


Ass-Gasket (dust seal at mount)



Noises When Shaken

Delicate clicking from the diaphragm blades.


Made in



Sharpness      performance     top

Warning 1: Image sharpness depends more on you than your lens.

Warning 2: Lens sharpness doesn't mean much to good photographers.

With those caveats, the 20mm f/4 AI is as sharp as all the rest of Nikon's 20mm lenses. I'm amazed at how similar they are when I did a run-off of about seven Nikon 20mm lenses and zooms.

All are as sharp in the center; the only difference is that the 16-35mm VR and 14-24mm are a bit sharper in the corners of FX wide-open. At actual shooting apertures like f/8, they are the same.


On 12MP FX (D700, D3)


At f/4

Sharp and contrasty center, perfect.

Softer sides and softer, darker corners.


At f/5.6

Sides and corners a bit better than at f/4, and lighter, too.


At f/8

Sides and corners better than at f/5.6, and all falloff is gone, too.


At f/11

The sides and corners are just about at their best. This and f/8 are the optimum apertures.


At f/16

Diffraction limits performance more than the optics themselves in the center, while the sides and corners get slightly sharper.


At f/22

Diffraction limits performance.


On Fuji Velvia with a 22x Loupe

I get very good performance even at f/4. I use it at any aperture, I see very little sharpness variation with aperture.

f/4: great in center, mild coma in edges but mostly lateral color. Some light falloff.

f/5.6: pretty good out to edges, a little light falloff.

f/8 and up: great performance all over


Sunstars      performance     top

The 20/4's straight 7-bladed diaphragm, makes great 14-pointed sunstars on bright points of light.


Compared        top

Intro    Specifications    Performance   Compared   Recommendations

Oddly, I carefully compared this to eight other Nikon fixed 20mm and ultrawide zooms, and except for the superior 16-35mm and 14-24mm, they are all pretty much the same sharpness overall!

I compared the 20/3.5 UD, 20/4 AI, 20/3.5 AI, 20/2.8 AI-s, 20/2.8 AF, 20-35mm, 17-35mm, 18-35mm and 14-24mm. Wow! Yes, they were all different, but different in different ways in different places, thus in all, they were each as sharp as the next. (The 16-35mm and 14-24mm were superior, but everything else was the same.)

Sharpness Comparison to other 20mm lenses

20mm lens falloff comparison

Zeiss 21mm Comparison

23.9 oz.
7.040 oz.
9.1 oz.
8.2 oz.
7.4 oz.
13.7 oz.
Price, USA,
September 2010


Recommendations       top

Intro    Specifications    Performance   Compared   Recommendations

The Nikon 20mm f/4 AI is a manual-focus only lens. For compact travel, it's the best Nikon ultrawide ever made, with the 20/3.5 AI as an almost identical second place in size.

This lens also showed me the complete lack of correlation between appearance (what camera dealers call "condition") and performance. I have had two of these lenses. The first one I bought used for $300 from a prominent Palo Alto, CA dealer in 1993. It looked completely unused. Its performance was worse than the beat-up one I use today as pictured above. The lens I use today looks much more beat up and cost me only $150 from a stranger, also in 1993. It performs much better. These differences are due to manufacturing variations. The only way to see how well a lens works is to photograph with it. Luckily the dealer who sold me the nice looking but poor performing 20mm took it back.

On 35mm, I can handhold it with sharp results 70% of the time at 1/8 on a Nikon FA. It's always sharp for me at 1/15 on an FA.


Deployment      top

I'd pitch the flat Nikon cap that came with this lens new, and get a new "pinch" type cap. I'm not kidding: the new fatter caps are much easier to use in the field.

I'd leave either a 52mm Nikon Clear (NC - UV) filter, or a 52mm Hoya Super HMC UV on the lens at all times. I would leave the hood at home.

For color slides like Velvia 50, I use an old Nikon A2 or new 52mm Hoya HMC 81A outdoors.

For B&W film outdoors, I'd use an old Nikon Y48 or O56, or a new 52mm Hoya HMC K2 Yellow or 52mm Hoya HMC Orange.


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Mr. & Mrs. Ken Rockwell, Ryan and Katie.


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