The F4 is at the same time the last Nikon pro-camera with conventional/analog controls, and the first offering most of the functions that modern bodies have made us familiar with (auto-focus, matrix metering, PASM multi-automatism, motorized film advance and rewind). It was also the last Nikon camera to enjoy (for a few years) an undisputed supremacy on the professional market.

In 1988, auto-focus was still in its infancy. Minolta had launched the Maxxum 7000 in 1985, and Nikon had followed with their first auto-focus SLR, the F501 (N2002 in the US) one year later. The F4 was the first implementation of  auto-focus on a professional SLR.

Compared to what was available in 1988, the F4’s auto-focus was not bad at all, but the arrival of the Canon EOS-1 one year later made it look slow and primitive, and today, the performance of its auto-focus system is what makes photographers think twice before using or buying an old F4.

The F4 is built around Nikon’s second generation auto-focus module, the “Advanced AM200”. Its single horizontal AF zone is composed of 200 CCD sensors, and the focus zone is very small  (probably 3mm wide and 1mm high – if the engraving on the viewfinder’s focusing screen is any indication). The module is shared with other Nikon auto-focus SLR bodies of the same period (F801/N8008, F601/N6006 for instance) but the F4’s auto-focus motor is stronger and the use of a 8 bit microprocessor makes the whole setup faster than on lesser cameras.

On the viewfinder’s focusing screen, at the place where the split image rangefinder would be on a manual focus camera, the AF zone is signaled by two small brackets engraved on the glass of the focusing screen. The markers of AF area are very difficult to see if the subject is poorly lit, and it can be difficult to visualize exactly where the camera is focusing (on modern cameras the active auto-focus zone is often surrounded by red LEDs. Nothing of that sort here).

So, is the auto-focus really that bad?

The F4 was famously launched at the Seoul Summer Olympic games.  Today, nobody would use a F4 to shoot sporting events with long tele-zooms, but in all fairness, with lenses of shorter focal distance,  the auto-focus is reactive and accurate. Its biggest weakness in my opinion is not its slowness, or that it tends to hunt if the scene is poorly lit. It’s that the AF zone is so narrow that you really have to pay attention to what part of the scene the AF sensor is pointed at. You can not simply point the camera loosely towards the subject, and expect the auto-focus system to locate it somewhere in the central area of the frame. You have to aim precisely at it, right at the center of the focusing screen, let the system focus on it, then keep the shutter release button half pressed  (to lock the focus) and re-frame your picture. In that sense, it’s more a focus-assist system (Nikon write about an “electronic rangefinder” in their user manual) than an auto-focus system as we know it now.

The N90S (F90X outside of the US) that came a few years later (1994) benefits from an auto-focus system of a newer generation: it still has a single zone auto-focus module, but it’s much wider (7 x 3mm), and is shaped like a cross (it can focus on subjects presenting vertical lines as well as  horizontal lines), even in low light and with slow (f/5.6) lenses.

The user experience is very different. The camera easily finds the subject even if not perfectly centered in the frame, and it focuses rapidly and accurately, even on mobile subjects moving erratically. In that regard, the N90S is already a modern camera.

Using the F4 as a manual focus camera

A common opinion in the forums is that you should simply forget about the auto-focus system, and use manual focus lenses on the F4. Even if it’s technically possible – the F4 accepts almost any manual focus lens ever made by Nikon (with very few limitations) – I’m not sure it’s a great idea: the viewfinder of the camera has not been designed for that.

In the days of manual focus cameras, manufacturers had to make focusing as easy as possible for the eyes of the photographer, and as result, they used to design viewfinders with a high level of magnification (0.9X) and they spec’d focusing screens to be as precise as possible, even at the cost of looking at bit dark and coarse. As soon as auto-focus systems became the norm, manufacturers adopted viewfinders with much lower magnification factors (0.7X), in conjunction with much brighter and smoother focusing screens, which had a more limited ability to show small differences in focusing. [more about the evolution of the viewfinders of SLRs over time]

The F4’s default viewfinder (the DP-20) and its default focusing screen (the BriteView Type “B”) are typical of an auto-focus camera. The DP-20 is a long eyepoint / low magnification viewfinder (22mm and 0.70X respectively), and the “Type B” focusing screen is bright but not very precise. The Type B provides none of the focusing aids you  find on a manual focus camera (no micro prism, no split image rangefinder).  It’s difficult to set the focus with the naked eye when you can’t or don’t want to use the auto-focus system.

Optional focus screens optimized for manual focusing were available from Nikon and from third party vendors (Nikon’s Type “K” and Type “P” focusing screens have a ring of micro prisms around  a split image rangefinder spot, the Type “J” just has a central micro prism focusing spot). Equipped with such a focusing screen, the F4 could be used as you would use a F3 or a FE2 – with the additional benefit of matrix metering. Those focusing screens are pretty scarce now, and are sometimes offered for more than $150.00 (they’re specific to the F4 – you won’t be able to focus accurately with a focusing screen designed for the F, F2 or F3).

On the F4 I bought, the Type B focusing screen had been replaced with a Type E. It’s a variant of the Type B with horizontal and vertical lines etched in the glass. If I mount a manual focus lens on the camera, I just use the auto-focus system as an electronic rangefinder – when the big green dot is on in the viewfinder, it’s focused. This “electronic rangefinder” is as good as a split image rangefinder – you just have to trust it.

More in a few weeks, with my take on compatibility, reliability and ….

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Early Nikon AF cameras and their AF modules

On a camera, the overall performance of the auto-focus system (and the quality of user experience) depend on much more than just the AF module.

• An auto-focus system is composed of hardware (the AF module with its CCD sensors, the microprocessors) and of software (the AF algorithm). It is  part of an even larger system (the camera itself with its other subsystems and its lenses) with which it has to integrate smoothly.
• As an example, an explanation of the AF performance improvements between the F90 (N90 in the USA) and the F90X (N90s in the USA), both equipped with the same CAM246 AF module (from a very interesting blog entry in 678vintagecamera.ca :”Improvements over the F90 included faster AF speed and tracking. Nikon claimed a 2x increase in CPU speed, a 25% faster AF lens drive speed over the F90, and a new AF algorithm.”Same AF module, dramatically improved performance thanks to hardware and software improvements. (source: https://www.678vintagecameras.ca/blog/forgotten-film-warrior-the-nikon-f90x-aka-n90s)

Nikon AF Modules (1986-1995)
Name of the AF module	Number of AF Points	Shape of the AF zone	Number of AF Pixels in the module	Nikon cameras equipped with the module	Launch year of the camera
no name	1	horizontal	96 horizon.	F501	1986
AM200	1	horizontal	200 horiz.	F401	1987
Advanced AM 200	1	horizontal	200 horiz.	F801, F4, F601	1988, 1990, 1991
CAM246	1	horizontal + vertical	172 hor; 74 vert;	F90, F90X	1992, 1994
Multicam 1300	5	multiple horizontal +vertical	1300	F5, F100	1996, 1999

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