Both projectors take a pass in this category. They are both entry level projectors, and while they have the usual sharpness, and other controls, including some which are dynamic, there's really nothing much to talk about here.
The one exception would be the Optoma HD20's ImageAI. I've mentioned it above, but want to clarify. ImageAI is not a dynamic iris. Rather, ImageAI controls lamp brightness, raising and lowering it to suit the scene. In this regard, it's purpose and results aren't completely different than using a dynamic iris.
Unfortunately, the HD20 takes a long time after a scene change (from darker scene to brighter, or the other way around), to react. Sometines, it can be as much as 8 seconds, or even longer. Then, the image snaps brighter or darker to match the new scene. That would be great if instantaneous but not 3 or 8 seconds later, then it just looks bad.
By my take, the ImageAI on this projector is distracting, and that distraction is a bigger issue than any improvement in blacks that the ImageAI provides. I recommend not using it, but try and decide for yourself.
Optoma HD20 vs. Mitsubishi HC3800 Bottom Line
The Optoma HD20 is one of (so far), three under $1000 projectors. For about $300 - $400 more, you can instead choose the HC3800. While the Optoma is a great way to get into a full 1080p projector on the cheap, that HD20 just isn't much of a match for the HC3800. Seems the HC3800 does just about everything as well or better than the HD20, and that big black level difference definitely should allow most of us to rationalize that modest price difference.
Two last images (a little rock and roll): The first is the Optoma HD20 showing two of the Moody Blues in concert, followed by Pete Townsend of the Who, on the HC3800 projector:
The HD20 makes a great projector for your $999 (and be sure to read the three way comparsion with it doing battle against the Vivitek and the BenQ - the other under $1000 projectors in 1080p space.