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Nikon CU-1 Focusing Unit
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Nikon CU-1 Focus Unit

Nikon CU-1 Focus Unit. enlarge.

July 2008    More Nikon Reviews

Introduction       top

This weird thing is the rear half of Nikon's first modular 400mm f/3.5 Q, 600mm f/5.6 P and 800mm f/8 P lenses of 1964.

The front half of each of these three lenses were the optics. This gizmo was the same for all three lenses, and held the focus and aperture mechanisms.

By using three different heads and the same back-end, you could use all three lenses but only have to by one rear half. This saved you money, since half the expense of a lens are these mechanics. You also had less to carry out to a job, since you only needed to carry one or two extra heads instead of carrying entire lenses.

It has strap lugs, making a lens change even easier since you can change the heads without removing the strap from around your neck, or the focus unit from the camera!

This CU-1 was eventually replaced by the AU-1 Focus Unit, and all this cockamamie stuff was eventually replaced by lenses that didn't unscrew into two halves.

CU-1 and 600mm f/5.6

Nikon 600mm f/5.6 head (above) and CU-1 Focus Unit (below). enlarge.


Metering       back to intro     back to top

There is no meter coupling. You must meter stopped-down. See my 600mm f/5.6 P review for instructions on how to meter with modern cameras.

Nikon CU-1 Focus Unit

Front, showing diaphragm, Nikon CU-1 Focus Unit. enlarge.


Aperture Setting

Controls, Nikon CU-1 Focus Unit

Controls, Nikon CU-1 Focus Unit. enlarge.

The CU-1 goes from f/4.5 to f/22. This same ring is used regardless of the speed of your lens head.

If you set an aperture faster than your lens, you don't get the faster aperture.

With the 400mm f/4.5, they all work.

With the 600mm f/5.6, ignore the f/4.5 setting. It does the same thing as the f/5.6 setting.

With the 800mm f/8, ignore the f/4.5 and f/5.6 settings. They do the same thing as the f/8 setting.


Focus Scales

Focus Scale, Nikon CU-1 Focus Unit

Interchangeable Focus Scales, Nikon CU-1 Focus Unit. enlarge.

The CU-1 comes with three metal focus scales. You attach whichever you like with the two screws seen at the top center above.

There is no hard infinity focus stop.

You may calibrate the scales by loosening the two screws and sliding the scale until it reads correctly. Don't do this unless you have access to the moon, or something clearly visible at least many miles away.

If you're shooting sports and swapping heads, I guess you can do without changing the scales each time.


Specifications with commentary        top

Optics: None, just a hole with a diaphragm and a helicoid focuser.

Diaphragm: 9 conventional blades. Stops down to f/22.

Aperture Ring: Yes; full-stop clicks.

Filter Thread: None; use the 122mm thread on the front of the lens unit.


Close Focus:

   400mm: 16 feet (5 meters).

   600mm: 35 feet (11 meters).

   800mm: 60 feet (19 meters).


Maximum Reproduction Ratio:

   400mm: 1:11.

   600mm: 1:16.

   800mm: 1:20.


Hard Infinity Focus Stop? No.

Depth-of-Field Scale: No.

Infra-Red Focus Index: No.


Size, measured, focused at infinity: 12.05" (306mm) extension from flange, 12.36" (314mm) overall. 4.49" (114mm) diameter, maximum including knobs. It gets longer as focused more closely.

Weight, measured: 3 pounds, 1/2 oz. (1,380g), including strap.

Rear, Nikn CU-1

Rear, CU-1 Focusing Unit.


Performance       top

See my 600mm f/5.6 NIKKOR-P review.


Recommendations       top

If you have one of the lens units, you need this to take pictures. If not, maybe you can turn it into a musical instrument.



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