Stop down metering question

I've dusted off my old Nikon F2S to shoot some film. I have a few non-AI lenses for it but wanted to try some other lenses I have; in particular, a Series E 100mm f/2.8 (since I regrettably sold my Nikkor 105 f/2.5 many years ago).

The Series E should function properly on my F2S using stop down metering. I just had it outside to take a look. With stop down metering, I was getting readings that seemed like they would produce overexposure. Out of curiosity, I mounted a non-AI Nikkor 50mm f/2.

I took the reading on a scene, then pushed the DOF preview button. The meter then showed approximately one stop underexposure. This had me thinking that if the original meter reading was accurate, why would it change when the lens was stopped down to the actual aperture the meter had suggested would produce proper exposure?

And therefore, wouldn't this behavior indicate that all shots taken using stop down metering would be a stop overexposed?

Apparently, there's something about the process that I don't understand... can anyone explain this to me?

Thanks for any insights,

Bob

You cannot directly compare the readings of a Nikon F2S meter between an uncoupled Series E or AFD lens (no rabbit ears on aperture ring) and a standard AI or pre-AI Nikkor (that has the rabbit ears). The lens with rabbit ears mechanically interacts with the meter prism. the earless lens does not, and this affects the reading when you press the DOF button.

Also, the Nikon F2 series can be a little tricky: it is easy to forget that stop down mode doesn't necessarily kick in automatically with the appropriate lens. You (usually) need to manually "tell" the camera you want to use it in stop down mode before it will give accurate readings. The way you do this is not at all clear if you've lost the instruction book: the setting isn't made by an obvious control, so can be rather obscure depending on the specific F2 body/meter prism combo.

To invoke stop-down metering mode with the (pre-AI) F2 Photomic, F2S, or F2SB (DP1, DP2 or DP3): remove the uncoupled lens (if you have one mounted). Look at the tiny aperture window on the front plate of the prism. For accurate stop down metering, the aperture displayed in the window MUST be 5.6 (with any lens). If you see any number not 5.6, use your fingernail to press up on the prism/lens coupling pin (centered underneath the front prism overhang) until you hear a click and the window jumps to 5.6. You can then mount your "non-rabbit-ears" lens (Series E, AFD, uncoupled Tamron, etc), and meter readings will be accurate when the DOF button is held down. If using uncoupled extension tubes (M2 ring for the Micro Nikkor, the K set) or bellows, you do not need to hold down the DOF button when metering: those accessories stop the lens down to working aperture by default. Note the camera will automatically revert to normal full-open-aperture metering mode as soon as you mount and index a different lens that has the "rabbit ears" metering shoe on its aperture ring (so, accurate stop down metering via DOF button is literally impossible if the lens has rabbit ears). You must remember to press the prism pin to set it to 5.6 each time you switch from a coupled lens to an uncoupled lens.

To invoke stop down metering mode with the (AI-capable) F2A or F2AS (D11, DP12) BEFORE mounting ANY non-AI pre-AI lens: use the top of your fingernail to press up on the silver AI meter coupling tab located at right front of the prism overhang (under the serrated slide switch). The tab can be a bit fussy: you need to make it latch in its deactivated position (tucked up and hidden inside the prism). Once the tab is securely latched out of the way, you can mount your non-AI pre-AI lens or extension tube. Press the DOF button to get accurate stopped down meter readings. Note these AI models of F2 do NOT automatically revert back to wide open metering when you mount an AI lens: you must first slide the serrated switch to the right to drop the AI coupling tab back into position (if you forget to do this and don't stop down the AI lens while metering, readings will be way off).