Stop-down worries

I wonder if anyone else has experienced this. Before I "went digital", my travel lense was a Sigma 28-200mm Aspherical Macro that always gave beautiful Fujichromes. When I got my D700, I thought the images were always just a tad over-exposed. I recently got a Nikkor 28-200mmG and did a side-by-side test shoot.
At each comparable focal length, at the same aperture setting and shutter-speed (as per Nikon View NX2), the Sigma is consistantly 1/2 to 1 stop "lighter" even tho View NX says that the exposures were identical.
My thoughts are that the Sigma isn't closing-down to the proper F-stop that the D700 sets where, on film cameras where aperture was set via the lens, it did fine. Has anyone else noticed that maybe "third-party" lenses don't close down to the correct "shooting aperture" when the camera sets the F-stop?

While I've not noticed this with my Sigma 10-20 on my D7000 I do recall reading about the exposure differences between 3rd party vs. "branded" lenses. If memory serves, I believe the consensus was that usually the situation was due to an older generation 3rd party lens not being quite in sync so to speak with the newer camera bodies. That is, the chip inside the lens may not be properly calibrated to the vagaries of the new camera body in question. If that is the case, perhaps you could call Sigma to confirm and if so, they may re-chip the lens for you for free or a nominal price.

Just a quick thought: which metering mode are you using? I find Matrix metering to be generally effective but sometimes a bit schizophrenic so I would use Centre Weighted for a more stable and reliable results when comparing the lenses.

I hope you might find some of this useful.

Regards,

Thanks for the info. Hadn't heard about that "older chip" thing. I did wonder if a different meter-mode would help, so I did the test-shoot in Matrix, Centre-weight and Spot as well as in Aperture Priority and Manual Exposure modes. Results were all the same which led me to think that the aperture wasn't closing down quite far enough; a shame since the lens is so sharp and doesn't have the problem with straight lines that the Nikkor G shows.