DIY Nikon AI modification
- by Lars
This is NOT meant
as a general outline of the AI modification procedure but merely as an
illustrated report from my first attempt with this subject.
As Nikon released the AI
lenses in 1977 they offered a modification of (most of) the pre-AI lenses
flyer and lens
chart @ www.aiconversions.com).
The modification consisted of an aperture ring replacement - the new one
having a METER
COUPLING RIDGE, an EE
SERVO COUPLING POST and ADR (=Aperture Direct Reading) numbers. The
modified lenses were not fitted with a LENS
SPEED INDEXING POST however, but see why this is otherwise a good idea
in some cases HERE.
days one should be lucky to find a repair place with these modification
kits still in stock, but there is no need to despair. It is not that difficult
to AI modify. I recently modified an old NIKKOR-S Auto 50mm 1:1.4 (kindly
given to me by Alasdair Mackintosh), and here is what I did:
||At first I called the local
Nikon agent (DFA) in
Denmark and asked for the price of an AI modification kit for this particular
lens. Surprisingly they still had it in stock but they were asking 350
dkr (= 43 US$). I found that way too steep (although it is probably
fair considering the original prize, see the lens
chart), so I got my tools out of the box.
|FIG. 2 - Lens mount detachment
||To remove the lens mount
I unscrewed 4 screws leaving the one at 6 o'clock (see fig. 2). This screw
holds the spring that loads the aperture action lever and is not attached
to the lens body.
|FIG. 3 - Aperture ring screw
||I then removed the screw
that transfers the aperture ring position to the aperture setting mechanism
(see fig. 3).
||The aperture ring was however
still held by a retaining ring (see fig. 4).
|FIG. 5 - Securing screw (1)
||To get the retaining ring
off I had to remove the METER COUPLING PRONG as it covered a little hole
that allowed access to a securing screw (see fig. 5).
|FIG. 6 - Securing screw (2)
||The tiny securing screw
(fig. 6) and the retaining ring was only used on the early version of this
lens (with serial # bellow 635511 the repair manual says).
|FIG. 7 - Retaining ring detachment
||Lacking a better tool I
used a pair of scissors to unscrew the retaining ring (fig. 7).
|FIG. 8 - Disassembled lens
||Now I had the lens disassembled
and ready for modification (fig. 8).
|FIG. 9 - Filing the aperture ring
||I used a simple file to
remove about 1.5 mm of the aperture ring edge from f/8 to about three stops
on the other side of f/1.4 (see fig. 9 & 10),
thereby leaving a METER
COUPLING RIDGE having a leading edge with a 5 f-stop offset (f/8) compared
to the maximum aperture (f/1.4). Lenses with a maximum aperture worse than
f/1.8 should have a 4 and 2/3 f-stops offset.
|FIG. 10 - Crude AI modification
||The lens was now crudely
AI modified and ready for use with the major part of the AI coupled cameras.
I still lacked a few details to call this a full
AI modification though.
|FIG. 11 - EE servo coupling post
SERVO COUPLING POST was 'added', again by simply removing part of the
aperture ring edge (fig. 11). I positioned it by eye using a NIKKOR 35mm
1:2 (AI-S) as a template. I am not sure how exact its position must be
- but I am not likely to ever need it (in connection with a DS-12 Aperture
||Black touch up paint was
applied to the shiny face (fig. 12). I have later discovered that it
wont bind, so I might need some special aluminium paint, see figs. 16
|FIG. 13 - Preliminary result of (my first) AI modification
||The modification was refined
a bit but I was still lacking some important details; ADR numbers, a METER
COUPLING PRONG, and perhaps most important to me a LENS
SPEED INDEXING POST. I seriously needed this to enable AMP (matrix)
metering with my FA.
|FIG. 14 - ADR strip from Tamron adaptall-2 added.
||I cannibalized an ADR strip
from a retired Tamron adaptall-2. The number alignment is not perfect as
the radii of the rings differ. The ADR windows are however wide enough
to allow for satisfactory viewing. Some people get the ADR engraved directly
into the apereture ring.
|FIG. 15 - Female F-mount ring marked with some LENS SPEED
INDEX POST positions.
||In order to find the exact
position of the LENS
SPEED INDEXING POST I detached the female f-mount ring of an E2 extension
ring. This ring was then mounted on a NIKKOR 50mm 1:1.4 (AI-S) lens and
the LSIP position was simply transferred to the ring. I have also transferred
positions for 1:2, 1:2.8, and 1:3.5 lenses (see fig. 15).
|FIG. 16 - Female f-mount ring is mounted to assist LENS
SPEED INDEXING POST positioning.
||For the LSIP itself I used
a screw - again cannibalized from the Tamron adapter (see fig. 16 &
This particular screw was useful as the top part of it was unthreaded.
It would therefore not damage the LENS SPEED INDEXING LEVER of the camera.
In addition it had a dull dark colour. With the mount detached (see fig.
I simply hand drilled a hole in the right spot considering the 1.4 LSIP
mark on the E2 ring and the radius of the screw.
|FIG. 17 - LENS SPEED INDEXING POST
||I checked the position using
my FA on S mode to see whether it would choose 1:1.4 before jumping to
a slower shutter speed when the lighting got lower - It would indeed choose
1:1.4 as the widest aperture before shifting the shutter speed! The LSIP
was successfully positioned and I now get AMP (matrix) as with any post-AI
lens with my FA. I still miss one detail though; the METER COUPLING PRONG
or SHOE for use with pre-AI cameras.