Author Topic: Ai-P lenses - CPU modification  (Read 4382 times)

Erik Lund

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Ai-P lenses - CPU modification
« on: June 11, 2015, 15:35:37 »
This is meant as an addition to the topic: Chipping a Nikkor: A walk-through

Ai-P lenses

Nikon have only implemented a CPU chip in three Manual Focus lenses;
45mm 2.8 Ai-P, 500mm Ai-P 4.0 and 1200-1700mm Ai-P 5.6-8.0

Many manual focus lenses don't have a equivalent Nikon Auto Focus lens; Fisheye-Nikkor 8mm 2.8 Ais, and Noct-Nikkor 58mm 1.2 Ais, Medical-Nikkor 120mm 4.0 Ais and a list of third party special lenses like the Voigtlander Macro APO Lanthar 125mm 2.5 Ais, lenses for  IR and UV - The list is long,,,

The CPU in a Nikkor lens auto focus or manual focus contains the specific properties of that lens, it contains information to the camera to be used for calculating the exposure and general functions like auto focus, scene recognition, evaluating the return light from the pre flash and more.

The data contains: The lens ID number, exit pupil size, maximum and minimum aperture, focal length, distance information, type of lens; MF/AF/AF-D/AF-I/AI-P/AF-S/AF-G/PC-E/E-Type and G-Type also information on calibrated auto focus characteristics such as in-focus point indication.


A dream camera for Ais lenses, since you can use Matrix metering. F4 will default to "A" if set to "P" or "S" and an Ai/Ais lens is attached. Same as the high-end DSLRs, in fact.

F5 and D1
The F5 the D1 series cameras; D1, D1H and D1X where crippled and the reason the CPU chipping of manual focus lenses escalated, they will only allow Colour Matrix metering when using lenses with a build in CPU.

The second scrolling wheel, used for setting the aperture value from the camera is responsible for this, the cost saving of omitting the aperture ring of the G type lenses prevailed backward compatibility.

F6 and D2
With the introduction of F6 and the D2 series cameras it was now possible to enter the data of 10 Ais/Ai lenses into the cameras menu thereby releasing the ability for 3D Colour Matrix metering.

However this only works if you remember to select the correct lens will this work, definitely still not a professional practical solution.

When using the TC-E teleconverters the information on the properties of the lens and converter is relayed to the camera, sometimes the teleconverters miss inform the camera about the focal length but usually this is not so important for long focal lengths, since the scene usually is very compressed and at a great distance.
It is however very important up close, portraits and macro shooting.

CPU Chipping
Most manual focus lenses can be modified/upgraded with a CPU. The most important aspect is free space, is there room for the contact block, often you have to remove, grind material off, the mount and the rear lens group. Also the aperture linkage or parts of it must sometimes be repositioned to make room.

Donor lens CPU
A cheap solution, if you have access to scrapped lenses is to use a CPU print boards from similar AF lenses and implemented them into the manual focus lenses. For AF-D lenses and zoom lenses you will have to short out the circuit board at the appropriate zoom and distance setting, also the camera will think that it is a auto focus lens and sometimes even try to run the screw driver to achieve focus.

Custom CPU chip
Custom CPU and print boards have now been developed, several solutions has evolved;

The type of CPU chip that Bjørn Rørslett uses in the topic: Chipping a Nikkor: A walk-through can emulate the functionality of all types of lenses. Ais, Ai and Ai modified lenses can be used, as long as you set the aperture value via the aperture ring on the lens.

Even non coupled lenses, like the Macro-Nikkor lenses can be used for instance with CPU chipped extension rings and/or bellows. These custom print boards with CPU are so small that they fit inside a normal AFS contact block, truly a very flexible modular solution.

The other type is the "do all" Dandelion, a CPU and print board build into an ready to install contact block.

The block consist of two halves glued together around a print board with the CPU and with coil spring loaded contact pins. It is glued onto the mount using a supplied jig that holds the contact block, and if necessary a small distance piece, in place during the hardening of the glue.

After installation the CPU is programmed via a series of combinations of shutter and aperture settings performed with the camera. The Dandelion CPU can only emulate a manual focus G-Type lens, it has focus confirmation and will work in P, A, S, and M mode. You can't use the Dandelion for Ai or Ai modified lenses it will result in wrong exposures due to the non-linear movement of the aperture leaver.

The Dandelion is a very fragile design, easily damaged or knocked off by impact. These CPU's are similar in size to the 5 pin AF contact blocks, but without the lower part that rest against the inside of the F-mount.

This is written from memory, I could be wrong about some of the functionality, if you have any corrections please do not hesitate to post them and I will edit the post, thanks!
Erik Lund