Black Levels and Shadow Detail
The EP1690 claims a contrast ratio of 2500:1which is common for business DLP projectors. In Cinema mode, black levels are very respectable but by no means exceptional. Interestingly, I would say that the black levels were not as good as the competing, but more expensive Mitsubishi HD4000, just as Optoma's HD72 home theater projector can't match the black levels of Mitsubishi's HC3000. In both cases, the Mitsubishi projectors are significantly more expensive (by about $500). As you would expect, shadow detail, while good, could also be better. In the brigher modes both black levels and shadow detail diminishes, which you can see if you view in a darkened room. Of course, if you are using the brighter modes, most likely you will have ambient light to deal with, and both black levels and shadow detail will be lost regardless.
Shadow details leave a bit to be desired, but I must apologize, the "overexposed" image wasn't as overexposed as I had inteneded.
Based on that, the chances of it bothering you are slim, but a projector with a faster wheel, or an LCD projector tend to solve the problem, if a 2X machine isn't for you. Unless you are familiar with your reaction to the rainbow effect, if you are buying online, it's important to make sure the company you buy from is reasonable in handling an exchange, etc. should rainbows be a problem for you.
So, ultimately the EP1690 does an impressive job as a very affordable widescreen business projector, and also is the lowest cost widescreen projector that can actually put out 2000 lumens (ok, 1900+). Add to that particularly good color handling (noteworthy reds and yellows), for business, and you have a very versatile projector.