dante stella stories photographs technical guestbook

This will add considerable spice to the next package tour.
45mm f/2.8 GN-Nikkor

Important: you must have this lens modified (whether by a now-scarce factory kit or cutting) before trying to mount it on any camera that has a fixed AI-coupling ring around the lens mount.

One thing you have to admire about Nikon is the ability to market the 45/2.8P lens.  A simple Tessar with a slow maximum aperture, no ADR numbers, and a thin focusing ring, commands hideous prices in a black finish.  At the same time, the lens it so shamelessly emulates, the 45mm f/2.8 GN-Nikkor, languishes on store shelves and on Ebay.  Part of that might be that some sellers are asking astronomical prices for a lens that, absent AI modification (which may be as simple as a $40 "circumcision"), cannot be used on any Nikon digital camera. 

But either way, the small, slow, simple prime lens is making a comeback.

A stab at the history.  The 1971 GN Nikkor was reportedly the cheapest lens Nikon made, but it probably also qualifies as one of the most interesting.  In 1969, a group of Nikon engineers was probably sitting around a conference table smoking Mild Sevens by the dozens.  The problem at hand was flash control.  At that point, Nikon had the SB-1, its first electronic flash, with an amazing guide number of 28 (in meters).  With no TTL and no automatic flash capability, it was necessary to reset the aperture every time the subject distance changed.

This was the conversation:

First Product Planner: why is the flash system on the Canonet better than it is on the F series cameras?  I mean, the aperture of the camera automatically adjusts to provide the right flash exposure at any distance! Our users have to manually compute guide numbers in their heads.  Or buy Vivitar 283s!

First Engineer: (takes a drag) well, the alien TTL technology will arive here in 1983.  The SB-2 and SB-3 aren't even in the planning stages.

Second Planner: we can never cede the technological high ground to Canon.  Those fools will probably use a flamboyant tennis player as their spokesman in as few as fifteen years! (Reaches for his Scripto lighter).

Second Engineer: we could build such a system into an SLR.  We could

First Planner, First Engineer and Second Planner (in unison): Shut up!

Second Engineer: — link the focusing and aperture mechanisms.

First Engineer: — but on our lenses, that would lead to big apertures at close distances and small apertures at long distances.  No good.

Second Engineer: We'll simply reverse the focusing direction.

First Product Planner (gasping): But that will make it the same direction as Canon and Leica?

Second Engineer: Precisely.

What came out of this (or some similar) meeting was one of Nikon's smallest lenses (and certainly the smallest lens that Nikon actually made itself).  It is also one of Nikon's most unusual.

Dimensions and handling.  The GN-Nikkor is a tiny lens.  It extends only 18mm fore of the lens mount.  By comparison, the 50/1.8 Series E (widely and incorrectly believed to be the most "pancake" of them all) is a whopping 24mm. The Cosina-made 45mm f/2.8P is one millimeter shorter (at 17mm), though omitting a couple of features (more on this below).

To understand the compactness of this lens, first imagine that the front of the focusing ring is almost dead level with the optical barrel.  There is so very little room to grip this lens to put it on the camera that Nikon put two lovely bright knurled grip points on the barrel.  But despite the compactness s, there was enough space on the aperture ring to put Aperture Direct Readout (ADR) numbers on the AI conversion rings (this, along with a spot to put a metering prong, was discarded wholesale on the modern reincarnation).

The lens has two modes: ambient and flash.  In ambient mode, the lens operates like any other Nikkor - with two exceptions. One is that the focusing runs in the opposite direction from other Nikkors.  The other is that the pitch of the helicoid changes to being very slow once the lens is turned past 15m toward infinity.  This means that turning from, say, 15m to 20mm makes the lens barrel move very, very little.

To engage flash mode, you would turn the lens upside down, use the focusing ring to center a pointer on the guide number (GN) of your flash (or the closest one to it), and then push a small tab down to lock it.  From this point on, the focus and aperture ring move together so that as you focus closer, the aperture gets smaller (and vice-versa).  Note that as you focus, the aperture ring will click as it passes the numbers. 

Optical observations.  This should have more than enough resolution for most uses involving film and conventional processing.  Like any Tessar,  this lens comes into its own optically at f/4 and performs at its best at around f/8.  Depth of field increases all the way to f/32, but the lens gets noticeably less sharp by that point.  Of course, f/32 presupposes party flash pictures in flash mode, and in that context, sharpness may be a secondary concern.

On digital (tested on a D700), the lens has noticeable focus and illumination falloff from center to edge f/2.8.  Optical performance is very sharp by f/4, and the vignetting really starts to go away by f/5.6.  Modern cameras with AI-lens capability (like the D3/D3x/D700) have no problem working with this lens. Focusing on the groundglass of a D-series camera is not that easy.  The AF-assist brackets, though, can be set for off-center subjects, which partially counteracts the curved focusing field at f/2.8.

In terms of its resolving power on digital, at its minimum focusing distance, set to f/2.8 and pointed at a subject like a $2 bill, the lens will resolve enough to generate moire on a Kodak 14n sensor.  This suggests that although this does not come off as blazingly sharp on the D700 (with antialiasing filter), it does resolve quite a bit.

Flare resistance is excellent, as can be expected from small maximum aperture, a deep-set front element, and a low element count.

Flash mode.  Today, with TTL, D-TTL and i-TTL flash, one would wonder why you would bother with the "flash mode" of this lens.  The simple answer is that all TTL and automatic systems are fooled by subject reflectivity.  Shoot a white object, and it will tend to come out grey.  Shoot a black object, and it will tend to turn out grey.  Five million years ago, people simply divided the guide number of their flash (or flashbulb) by the subject distance to reach the aperture.  When shooting in a dark environment, this leads to accurate rendition.

The one key limitation of this system, though, is that with a lens that runs from f/2.8 to f/32, not every flash will allow shooting at all distances.  For example, at GN16 (in meters, approximately the power of the built-in flash on a D700), focusing will go from 0.8m to 6m (at which point you are at f/2.8 and the lens cannot turn further.  At GN80 (in meters), the lens will focus from 2.5-30m.  This is just physics.

Note also that the guide numbers on the lens are for ISO 100.  Here is a very rough computation of how you would set this lens at different film speeds.  Note: if shooting negative film, and your flash's guide numbers fall between two values on the lens, choose the higher one.  If shooting slides or digital, pick the lower value.  Check your flash's documentation to verify guide numbers.  Better yet, verify them yourself with a flash meter.

Note that you must multiply these values by 3.3 to get GN in feet.

@100 (m) @200 @400 Flashes closest to this value
10 14 20 SB-30
13 18 25 D700 built-in
16 22 36 Konica HX-18
20 28 39  
25 35 49  
32 45 63 SB-20
40 56 78

Vivitar 283
Metz 45 Series

50 70 98 Metz 54 series
63 88 123 Metz 60 series
80 112 157 Metz 78 series

If you want any ambient background light, strongly consider turning on slow synch.  The flash function performs well with the built-in speedlights in Nikon digital cameras (set mode to manual, full power).  If you get underexposed pictures, move the GN setting on the lens down one notch.  If you get overexposed ones, set the flash power down a fraction (so, say to 1/1.3 or 1/1.6).

Important caveat: be careful focusing!  Because the aperture ring has click stops, the focus tends to "click" into place.  And with the generally slow pitch of the focus (it has to open the aperture according to the inverse-square law), it is east to let the lens pick your focused distance.  Resist!  The difference between one f/stop and the next on the focusing screen is 50% of the flash power.  So for the most accurate flash operation powerful, you must take your best effort at focus possible.

Modifiying the flash system: if your camera does not have an especially powerful AI coupling ring (or doesn't have one at all), you can eliminate the click-stops from the lens by taking off the mount and removing the small flat spring (with the point bent into its middle) that provides the "clicks."  But if your camera's coupling is too strong — or your lens' helicoid grease too thin — the camera will tend to focus the lens (and move the aperture) on its own. This should not be as big a concern on a cameras where you can flip the tab up (e.g., F3, F4). 

Compared to the new 45mm f/2.8P.  The current 45/2.8P is very slightly smaller, very slightly lighter, focuses slightly closer, does not stop down to f/32, lacks the flash function, and reasonably can be expected to have slightly better coatings and optical performance.

The new 45mm was designed to be sold with the FM3a.  It is a great lens for film cameras that were designed in the AI era.  It is not so good if you have an older camera with a metered prism that wants to connect with meteing prongs (since you can't even fit prongs to this lens). 

On a current Nikon DSLR (and not the cheap ones), the new 45mm provides only one additional piece of functionality over an AI-modified old one: providing a searchable metadata field for focal length. With a "chipped" lens, the lens used is recorded in such a way that you can search for that lens.  With an AI lens manually input into the camera, the focal length and aperture used are still recorded, but the name of the lens is not.  This is a relatively minor point - and Leica files have the problem on Lightroom - you can see the FL and aperture (aperture in Beta 3), but you can't search by lens.

The current 45mm f/2.8P doesn't provide any additional functionality on higher-end Nikon DSLRs because they can matrix-meter with any AI lens, not just ones that have chips.  And given that lenses with chips tell Nikon digital cameras to control aperture via the camera's dials and not the aperture ring, it may even be a liability for some people.  On Nikon DSLRs, where there is a custom function that would allow you to use the aperture ring to set the aperture, it is usually buried (a sub-setting of F9 on the D700).  And once you set that, you then have to use the aperture ring with all AF lenses that have aperture rings.  So between your AI lenses, your chipped non-AF lenses, your AF lenses, and your G lenses, it could get confusing at an inopportune time.

Recommended focusing screens: K, E, H, R.

Conclusion. In an era where you couldn't get a usable ISO 3200 out of a camera, you might have thoughts a lens like this was slow.  But today, it's a different story - and one of these on something like a D700 makes for a very flat package with very high quality results. Even for sunnier days with film, it's a great companion to an F3.  And if you come from the Leica world, this lens even focuses in the right direction!