Aperture for Nikon AI on n70

Hi
I put a recently acquired (MF) Tamron SP 35-80mm with an AI mount
on a Nikon N70 (F70).
On aperture mode with centre weighted metering, everything works well
except for one thing - the aperture value in the LCD and viewfinder reads
F- -.
Does anyone know if this is normal?
Thanks
Nav

Piggyme

Re: Aperture for Nikon AI on n70

"piggyme" <removethis_junk4nav@yahoo.com> wrote
It is.
The 'AI' mount transmits relative aperture information: the
camera knows how many stops from full open the aperture
ring is set to. The camera has no way of knowing the absolute
aperture the lens is set to.
The old forked 'NAI' lenses transmitted absolute aperture
information but the only finder that needed this was the
original Photomic with the external photocell. The TTL
Nikon F finders needed to go through 'indexing'
jiggery-pokery so the finder could get the needed
relative aperture information from the fork position.
The AI mount was designed to eliminate indexing, AI standing
for 'Automatic Indexing'. However, the absolute aperture
information was now lost.
AI lenses have small aperture numbers on the ring, these
are looked at by a small lens in the finder so the user can
see the lens setting in the viewfinder.
AF lenses transmit the maximum aperture of the lens via
electric contacts. The camera can then work out the aperture
from the position of the AI ring, indicating how much
the lens has been stopped down, and the maximum aperture
of the lens.
--
Nicholas O. Lindan, Cleveland, Ohio
Darkroom Automation
http://www.nolindan.com/da/index.htm
n o lindan at ix dot netcom dot com


Nicholas O. Lindan

Re: Aperture for Nikon AI on n70

Yes.
The AI coupling indicates relative apeture to the metering system. Most cameras
that used the AI coupling had little mirrors so that you could see
the F stop actualy set.
The autofocus lenses indicate the actual apeture to the camera using the
electronic contacts, which almost all AI lenses lack.
That's the main difference between Nikon and Canon, Nikon extended their
manual focus lens mount to accomdate AF, Canon abandoned it.
Geoff.
--
Geoffrey S. Mendelson, Jerusalem, Israel gsm@mendelson.com N3OWJ/4X1GM
IL Voice: (07)-7424-1667 Fax ONLY: 972-2-648-1443 U.S. Voice: 1-215-821-1838
Visit my 'blog at http://geoffstechno.livejournal.com/


Gsm@mendelson.com (Geoffrey S. Mendelson

Re: Aperture for Nikon AI on n70

"piggyme" <removethis_junk4nav@yahoo.com> escribió en el mensaje
...
Yes. It's normal for any AI or AIs lenses without electrical contacts.


TLR

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