Lens Test Glossary     About these reviews

get it here or here

get it here or here

INTRODUCTION

This is the same as the D lens, just without the fairly meaningless D feature. In fact, it is also has the same optics as the manual-focus 20mm f/2.8 lens, although the manual focus lens is better built mechanically and costs more.

The 20mm AF was introduced in the spring of 1989.

The internal, engraved metal focus distance indicator appears to be the same part as from the 20mm AI-s manual focus lens. Unfortunately, the outsides of this AF lens are plastic. The 62mm filter threads are plastic, just perfect for cross-threading.

SPECIFICATIONS

The lens has 12 elements in 9 groups.

It focusses as close as 0.25m or 10 inches. It has CRC, close range correction.

An HB-4 hood is attached by bayonet. I don't bother with one.

The diaphragm has 7 blades and stops down to f/22.

It is 2.7" (69mm) around by 2.1" (54mm) long and weighs 9 ounces (260 g).

Nikon Product Number: 1913, in catalog as of spring 2008.

PERFORMANCE

AF Speed

The AF speed is almost instantaneous on an F100. One full turn of the AF screw focusses the lens from infinity to 2.5 feet.

Falloff of Illumination

It has the usual illumination falloff at f/2.8 and it's gone by f/5.6 or f/8. The 17-35mm zoom is much better if this is important to you.

Filter Vignetting on Film

There is no vignetting when used with a Nikon brand filter. They are thinner than most other brands. I get slight vignetting with Tiffen, Hoya, B+W, Heliopan and most other filters. I have heard that the 62mm B+W slim mount polarizer works OK, too. I have not tried it.

Ghosts

It has very few few ghosts. You are pretty safe with the sun in your image. It has the best ghost performance of any 20mm I've tested, and second only to the 17-35mm AF-S You can forget the lens hood, you don't need it.

Sharpness

It has coma (fuzziness) wide open in the corners typical to Nikon wide angle lenses.

Stopped down a couple of stops it is very, very sharp.

Mine is a bit softer in the lower left than in the lower right corner. I also find that with a Tiffen 62mm filter that the upper right vignettes more than the other corners. This is most likely due to mechanical slop.

Distortion

It has a mildly complex distortion signature on film. It has some barrel distortion in the central area of the image, and tends to straighten out at the very edges. It has the same distortion at all distances.

On a digital SLR you can use CS2's lens distortion correction with a setting of +2.50 to correct it.

You can get the Panorama Tools coefficients here for use on the Nikon digital SLRs.

Those coefficients are

R 0.0063, -0.021, 0, 1.0153
G 0.0063, -0.021, 0, 1.0147
B 0.0063, -0.021, 0, 1.0143

Mechanics

As typical for an AF lens, there is enough play in the mechanics so even if the focus ring is held tight that one can jiggle the front of the lens around enough to move the image around a bit.

Close Focus

Close focussing is closer than I need it. The smallest horizontal field is about 11-1/4."

RECOMMENDATIONS

I used to use this AF 20mm all the time because it's small and easy to use. I'd rather tote it around instead of the fat $1,500 17-35mm AF-S Unfortunately, I'm stronger than I am lazy and now lug the 17-35mm around instead.

This lens is not quite as sharp as my old 20mm f/4 AI manual focus. It's not quite as good as the 17-35mm F/2.8 AF-S zoom, which may be a first zoom to be a tad sharper than a fixed lens. The zoom also has less light falloff at f/2.8. How about that!

Here's a trick: Get all your filters in 77mm size. Get a step-up ring here to allow 77mm filters to fit on this 62mm threaded lens. Now not only can you use any filter without vignetting, you can even use two 77mm filters at the same time without vignetting. Even if one of those filters is an ordinary thick-mount polarizer I still get away with just a little darkening of the corners.

I get sharp results handheld at 1/10 second.

What's this odd depth-of-field scale all about?

Depth-of-field scales are calculated by Nikon at the maximum limits of fuzziness people are likely to tolerate. They are not calculated to give you the sharpest possible result if you have a tripod.

You might think that stopping all the way down gives the sharpest result, however it may not due to an effect called "diffraction." This effect is the same as squinting your eyes too much: it just gets fuzzier.

To spare you a very long and mathematical story, just stick a little scale like this to your 20mm lens. Find the nearest and farthest points of your subject, and place them each an equal distance from the main focus index so that they each fall on an equal f/stop just as you would for the conventional DOF scale. Read the f/stop from this new scale, and set that as your aperture for the sharpest possible result considering both depth-of-field and the effects of diffraction.

F/22 is indicated at the ends of the scale, somewhat beyond what the window displays.

For instance, if you want everything from 3 feet to infinity in focus, set the lens to 6 feet and use f/11-1/3 or f/13. You don't need to worry about the fractions; either f/11 or f/16 will be fine.