How to use a non-AI lens on a Nikon FG

On 1/15/2012 8:45 PM, wrote:
Hello,

Is there way way I can use a Nikkor-P non-AI 300 mm 1:4.5 lens on my FG, using manual mode? I thought I might put a Series E AI 50 mm 1:1.8 on to tell me what shutter speed to use. I want to use my 300 mm wide open, so I would set the 50 mm to f/4 for this. Then I would tape the AI ring to the body to hold this position and install the 300 mm, and use the shutter speed indicated by the 50 mm.

Or do I have to compensate for the differences in maximum aperture?

Unfortunately, you can't safely mount a non-AI lens on a Nikon FG.
I would recommend converting the lens to AI, unless it's a pristine
copy of interest to collectors.

--
Mike Benveniste -- (Clarification Required)
You don't have to sort of enhance reality. There is nothing
stranger than truth. -- Annie Leibovitz

wrote:

Thanks MB. I know the manual says that, but I don't see any problem
with it. The bayonet mount works, and the lens does not appear to foul
any mechanism in the camera body.

There are three possible problems:

The first is that the AI sensor prong
on the camera will snap off if you mount a non-AI lens on the camera. It
was not designed to fold up, like the F3.

The second is that the internal mechanism of the FG may foul (mirror catch,
and other possible things) because the specs for the amount of space the
lens can protrude back into the camera changed. The lenses can not go as
far back on the FG as on a pre-AI camera.

The third is the meter system won't work, even if you AI convert it. You can
get the camera to function in f-stop priority, and it will probably give
you a decent exposure with color negative or black and white film, but
it may not give you the perfect exposure needed for slide film.

It absolutely will not give you a correct exposure in Program mode. It may give
you a proper exposure in terms of light, but the shutter speed/f-stop actually
used will be almost random.

This is because the FG has no proper way of determining the actual f-stop
used, it meters the light, decides upon an f-stop/shutter speed combination,
closes the diaphragm based upon a proportional guess and then re-meters for
the correct shutter speed.

The problem is that AIs lenses have exact proportional motion for the
diaphragm closure lever, AI lenses don't, and pre-AI almost none at all.
The pre-AI lenses were designed with two options, open (for metering and
viewing) and closed (for exposure).

If you really want to use pre-AI lenses, buy a cheap pre-AI body. Note that
any of them are at least 24 1/2 years old, so expect them to need some
work (new light seals, CLA) before using them for serious work.
Or buy a newer camera (F3/F4) that can be used with them.

Geoff.

--
Geoffrey S. Mendelson, N3OWJ/4X1GM
My high blood pressure medicine reduces my midichlorian count. :-(