Sandy Bloom, Ph.D. wrote:

I was told that using the AF older Nikon lenses requires one to "shut off"?
something on the aperure ring so the DSLR can use it accurately.

On a lens with an aperture ring, you set the lens to its minimum aperture
and leave it there, which allows the aperture to be set by the camera body.
Most (all?) of the autofocus lenses with aperture rings have a "lock" on
the ring to keep it in that position. On the lower-end bodies that require
the aperture to be set by the camera, you must do this in order for the
lens to work. On the D2-series (and possibly the D200?) you can use the
aperture ring itself in A or M mode if you want.

On the G lenses, with no aperture ring, which unfortunately seems to be
what Nikon is making now, this obviously doesn't matter. Those lenses
are always set at minimum aperture.

If you're curious, the reason the lenses have to be set at minimum aperture
for automatic operation is this: when you take a picture the camera has to
stop down the lens to the chosen aperture at the time of exposure. It does
this mechanically, with a lever. The lever will only stop down the aperture
to the point that the aperture ring is set, but no further, which enables
manual operation where the camera doesn't know what aperture the lens is set
for -- it can say "stop down to whatever is selected" by moving the lever
all the way. So, the only way the camera has the ability to stop down to
any aperture is if the lens is set at the minimum aperture. Then, the
camera can select any aperture according to how far it moves the lever.

The new (D2, D200) cameras can't do this with AI and AI-S lenses; with
those, you must set the aperture from the lens aperture ring. This is
because the new cameras don't differentiate at all between AI and AI-S,
and the aperture levers work differently. So you can't use P and S
modes, but then, who uses those anyway?

Use of the AI Nikon lenses requires setting the Nikon DSLR to "M", and
getting your light reading independently.

This is not necessary with the D2-series and D200; they can meter with
AI and AI-S lenses. With the others, yes, you lose the light meter due
to having no mechanical coupling and no electrical communication with
the lens -- the camera has no way of knowing what aperture the lens is
set for, or how far it's stopped down, so it can't determine exposure.
(It could use stop-down metering with DOF preview if Nikon wanted to,
but they evidently don't.)

--
Jeremy |