Nikon LSI mechanism

Nikon LENS SPEED INDEXING mechanism
- by Lars Holst Hansen

The maximum aperture is relayed to FA by means of the LENS SPEED INDEXING LEVER (384 in the Nikon FA Repair Manual). By means of a sprocket (389) it will slide along a comb (385) and thereby move a brush (386) along five bands on a switch board.

The contact bands (on B1003) will short with the ground band as the brush slides along (see the CODE TABLE).

For comparison Nikkormat FTN (the first camera with Semi-Automatic Maximum Aperture Indexing) has following settings for the maximum aperture:

1.2 - 1.4 - 2 - 2.5 - 2.8 - 3.5 - 4 - 4.5 - 5.6

Here intermediate maximum apertures are "rounded" up to the next smaller aperture (an 1.8 is read as 2).

But what is the information on maximum aperture used for? For an explanation go to the page on Full AI-modification

CODE TABLE FOR THE LENS SPEED SIGNAL IN FA

Maximum Aperture	A	B	C	D
-	0	0	0	0
1.2	1	0	0	0
1.4	1	1	0	0
1.8	0	1	0	0
2	0	1	1	0
2.5	1	1	1	0
2.8	1	0	1	0
3.5	0	0	1	0
4	0	0	1	1
4.5	1	0	1	1
5.6	1	1	1	1
8	0	1	1	1
11	0	1	0	1

0 = closed
1 = open