yeah, okay, wow @ those guys above. i think it's a safe assumption that you understand the d90 will not meter with those lenses -- any reading of your post at all would tell someone that.
hopefully i can provide some real help.
Hi I have a couple of old lenses from my wife's camera which I have
been trying out on my D90. The Nikkor F ?series 135 f2.8 which seems
to work.
hopefully, since both lenses came off your wife's FG, they're both AI/AIs lenses. please try to confirm this, as if you're using a pre-AI lens, you CAN DAMAGE YOUR CAMERA. do the aperture rings look the same or very similar, with a ridge that sticks out towards the camera for a portion of the circumference? if the aperture ring is the same width all the way around, do not mount this lens to your camera.
However the E-Series 50mm 1.8 does not change exposure at
all when the apeture ring is turned and also one needs to use ultra
fast shutter speeds in bright light.
on all AI/AIs lenses (including the series E), the aperture of the lens is strictly controlled by the aperture ring. the AI lenses are not designed to have their aperture controlled by the camera. but even the AIs (and series E) were designed to be used this way (by the FA and similar cameras), the aperture blades still snap to the smallest aperture unless there is a camera behind them to hold the DOF-preview lever in the "open" position.
when the lens is unmounted, and set to f/22, you should be able to see all the aperture blades and the aperture should be tiny when you look through the lens. if you then move the little lever on the back of the lens, you should be able to manually open it. mounted, the DOF preview coupling should hold the lens open until the picture is taken, when the iris will contract to whatever setting corresponds to your aperture ring. i have used AIs lenses (including the 50mm 1.8 series E) on both the d70 and d200, and this should be the way the d90 works as well.
if your camera is forced to take pictures at f/1.8 regardless of the setting of the aperture ring, it means one of two things has gone wrong. either your camera is broke (DOF coupler doesn't relax when the shot is fired) or the lens is jammed. considering that the other lens works fine, it's probably not your camera. mess with the aperture ring and DOF lever on the back of the lens, unmounted, and see if it behaves as described in the paragraph above. if it does not, and just stays open, your aperture blades are probably jammed, or stuck with oil and the lens is trashed.
if that's the case, don't feel to bad. they're incredibly inexpensive (but high quality!) lenses, and easily replaced. you can get the the AI or AIs long barrel version (the best versions) for about $60. or the AF-d version for a little over $100.
