Now, using the exact same exposure, I re-photographed the same frame, but with Panasonic's menu open. Since the Menu has very bright areas, the dynamic iris can no longer close down - resulting in blacks that are slightly lighter gray than the image above.
Overall, the black levels are very good on the PT-AE1000U home theater projector.
When comparing to my own BenQ PE-8720 a Darkchip3 DLP projector, the Panasonic, when it is able to fully engage the dynamic iris, produces blacker blacks than my BenQ. On other scenes, where there is a lot of bright, along with the dark, the BenQ - relying on the native advantage of DLP (especially Darkchip3), then produces the blacker blacks.