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

On 2012-01-16, 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?

The real problem is that a pre-AI Nikkor lens can break the auto indexing
lever on the camera. You don't want to do that. You can have the lens
modified (AI'd) if you want to use it on an FG. Unless the lens is a
collector's item, then you just want to put it on the display shelf.

Besides the breakage problem, your scheme won't work. The camera uses
the ring resistor to tell how far the lens is set from the lens's maximum
aperture, not the absolute aperture. The wide open position of the ring
resistor is the same for all lenses. The metering circuitry inside the
camera reads the light through the wide open lens, and the ring resistor
tells the camera to adjust the exposure for the stopped-down aperture.
Some Nikons for aperture priority autoexposure will read the light through
the stopped-down lens, but I don't know whether the FG is one of them.

Bud

William Hamblen wrote:

Some Nikons for aperture priority autoexposure will read the light through
the stopped-down lens, but I don't know whether the FG is one of them.

The farthest open spot on the sensor ring is after the "no lens" spot,
so the camera will detect that there is no lens or the lens has no meter
coupling at all, and assume that the lens is stopped down to working
apeture already.

The FG does not have the ability to stop down the lens manually for a reading,
so it will only work, if at all with the lens wide open (unless the lens
itself has a stop down lever).

Actually I can't remember a Nikon camera that had that feature. :-(

Geoff.

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

wrote:

Slides right by it.

Good, then it should not be a problem. It is however an unusal lens.


Actually, the AI lens goes farther back.

This is a real telephoto lens (one with a long real focal length and not
an short one with a longer effective focal length), which explains it.

"The real problem is that a pre-AI Nikkor lens can break the auto indexing
lever on the camera."

Break it how? It is operated by a spring. If somehow it was prevented
from moving no harm would occur. (As it happens, my non-AI lens
lever has been removed.)

What non AI lever? On the camera? The FG did not have one. The problem is
the AI sensor lever sticks into where the f-stop ring on the forked lenses
goes. I doubt it was on purpose, but that way a non-AI lens can be AI'ed
with a dremel tool if you know how to do it.

"The camera uses the ring resistor to tell how far the lens is set
from the lens's maximum aperture, not the absolute aperture."

I did not know that. So I would need to meter at the same number of f/
stops from maximum aperture that I intend to use, not the same f/#.

That's how AI works. The original method read the F stop off the lens
(using the fork) and you had to index it so that it knew the F stop you
were metering at.

F stops are really irrelevant in this case the meter only needed to know what
F stop you were at in relation to full open.

So that it "knew" the actual exposure would be 1/4 (2 stops down) and so on
depending upon where the lens was st.

This method does seem redundant though.
Isn't the max aperture already known to the camera?
Isn't that what the tab at the bottom of the lens opening does
as the lens is twisted on?

Actually it's a minimum aperture indicator. Was first used on the 4004, which
controlled the actual aperture via the electronic contacts on an AF lens.

That's the big difference between the Nikon and Canon AF lenses. After the
problems with the F3AF, Nikon decided to move controls to electronic and
the motors to inside the camera.

The difference raised the price of the cameras, but did two things. First the
lenses used rack and pinion focusing instead of a helicoid which made them
30% cheaper. The second is when faster autofocusing came out, you just bought
a new camera, and kept all your lenses.

Canon went the other way and put the motors in the lenses, which was a disaster
for early EOS buyers. I had both, but sold off all my Canon gear after two
years of waiting for lenses that were vaporware, while all they sold were
cheap zooms. :-(

To keep it relevant, the regular full frame AF lenses are AIS, so they
will work fine on your FG, except for the G ones.

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

On Mon, 16 Jan 2012 14:24:12 -0800 (PST), wrote:
: Thanks all. Very helpful.
:
: I have a Nikon F Photomic T with its original 50 mm and telephoto lenses, and a Nikon FG, with a 50 mm lens. Here is my comparison.
:
: The old-style rabbit ears tend to foul on the AI ring plastic tab just a little as the 50 mm lens is installed on the newer FG, but they can be pulled away during installation/removal to clear it. Not an issue at all on my old telephoto for some reason.
:
: There are stop-down levers in the same position on both bodies, but the newer FG lever is set deeper into the body, as measured from the front of the lens opening, by 1/32 to 1/16 inch. This lever is set well into the body and it doesn't seem like it could contact anything except the corresponding lever on the lens. (As mentioned, I don't even have this lens lever on my telephoto, although it was there originally. It's set permanently on full aperture now.)
:
: The mirror is set well away from the lens in both cases, so interference is unlikely.
:
: Mechanically, I don't see any issues, except possibly rabbit ears in some cases. Optically, if I place any AI lens on it, the camera will know its maximum aperture and so will correctly assess ambient light. Then it will know light on the film at any given aperture. If I set my AI lens to f/8, it should display a shutter speed for that aperture. Then if I tape the ring down and remove the AI lens, the camera will still think I plan to shoot at f/8. If I then install a different lens, manually set to that aperture, it should illuminate the film with the same amount of light, so that the original shutter speed should still work.
:
: Worth some experiments anyway.

Suppose it works. Is there any conceivable circumstance under which you'd find
it worth the trouble to shoot that way?

Bob

On 2012-01-16, Geoffrey S. Mendelson wrote:
William Hamblen wrote:

Some Nikons for aperture priority autoexposure will read the light through
the stopped-down lens, but I don't know whether the FG is one of them.

The farthest open spot on the sensor ring is after the "no lens" spot,
so the camera will detect that there is no lens or the lens has no meter
coupling at all, and assume that the lens is stopped down to working
apeture already.

The FG does not have the ability to stop down the lens manually for a reading,
so it will only work, if at all with the lens wide open (unless the lens
itself has a stop down lever).

Actually I can't remember a Nikon camera that had that feature. :-(

Geoff.


Your depth of field preview lever will stop down the lens. Whether the
TTL meter will read the correct exposure is another question.

Bud

On 2012-01-16, wrote:

"The real problem is that a pre-AI Nikkor lens can break the auto indexing
lever on the camera."

Break it how? It is operated by a spring. If somehow it was prevented
from moving no harm would occur. (As it happens, my non-AI lens lever
has been removed.)

You were lucky. The cam follower on the camera sticks up to engage
a cam on the lens. The old lenses don't have the cutout for the cam
follower and the rear of the aperture ring on the lens may crush the
cam follower on the camera body. This is why the instruction booklet
for your FG says in no uncertain terms never try to mount a non-AI lens.
Your particular lens might have enough clearance at the back to clear the
cam follower. On some camera bodies (F3 and others) you can flip the
cam follower out of the way. The meter prong on the top of a manual
focus Nikkor lens will not hit anything on an AI Nikon camera body.
I've put manual focus AI and AI-S Nikkors complete with meter prong on
all my AI Nikon camera bodies with no problems.

Bud

On 1/16/2012 6:09 PM, William Hamblen wrote:

Your depth of field preview lever will stop down the lens. Whether the
TTL meter will read the correct exposure is another question.

The Nikon FG does not have a depth of field preview lever.

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

On 2012-01-16 19:29:03 +0000, Geoffrey S. Mendelson said:

wrote:
[...]
This method does seem redundant though.
Isn't the max aperture already known to the camera?
Isn't that what the tab at the bottom of the lens opening does
as the lens is twisted on?

Actually it's a minimum aperture indicator. Was first used on the 4004, which
controlled the actual aperture via the electronic contacts on an AF lens.

AI was introduced in 1977 and was known as Automatic Maximum-Aperture Indexing.

It signals the wide-open f-stop (maximum aperture) via the Maximum
Aperture Indexing Post (near the bottom of the lens mount).

It signals the position of the aperture control ring, relative to
wide-open, via the meter coupling ridge.

With these two pieces of information, AI-compatible cameras are able to
determine the actual f-stop the user has selected on the aperture
control ring.

Cameras that offer P and/or S mode require that the aperture control
ring is set at the fully stopped-down position - the minimum aperture.
The camera is now able to determine the range of absolute f-stops
offered by the lens.

IIRC, these 3 features were first used together in 1982 by the FG, then

1983 FA
1985 F-301/N2000
1986 F-501/N2020 (AF)
1987 F-401/N4004 (AF)

The F-401 did _not_ control the lens f-stop via the electrical contacts
- I think you'll find that the only Nikkors having an electronically
controlled aperture iris are the PC-E series.

The FG and later cameras need to determine the actual rather than
relative f-stop in order to provide Program mode TTL OTF flash. It also
allowed the FA and some of the later bodies to display the f-stop
chosen by P and S modes.



AI-S lenses were introduced in 1981 (before the FG). These have a
standardized aperture stop-down lever enabling precise control of
f-stop by the camera in P and S modes. Using an AI lens may cause a
significant error between wanted and actual f-stop.

G lenses are not AI-S, but retain the standardized aperture stop-down
lever for precise control.

This "S" feature also enables the F-401 and more recent cameras to set
the f-stop via a control on the body, rather than the lens aperture
control ring, in M and A modes.


That's the big difference between the Nikon and Canon AF lenses. After the
problems with the F3AF, Nikon decided to move controls to electronic and
the motors to inside the camera.

The difference raised the price of the cameras, but did two things. First the
lenses used rack and pinion focusing instead of a helicoid which made them
30% cheaper. The second is when faster autofocusing came out, you just bought
a new camera, and kept all your lenses.

Canon went the other way and put the motors in the lenses, which was a disaster
for early EOS buyers. I had both, but sold off all my Canon gear after two
years of waiting for lenses that were vaporware, while all they sold were
cheap zooms. :-(

To keep it relevant, the regular full frame AF lenses are AIS, so they
will work fine on your FG, except for the G ones.

Geoff.