This BenQ HT4050 is a single chip DLP projector. As such we expect at least good sharpness, for, unlike 3LCD and LCoS there is only one chip, rather than having three chips (panels) to align. BenQ points out that their lens is all glass, a good thing, but high quality optics is more about the final design than whether all the elements are glass. Many, if not most projectors do use some non-glass elements.
Above are a selection of images including a couple of close-ups for considering the HT4050's sharpness.
Overall, I found the projector to be at least typically sharp, but there is at least a little loss of sharpness in the corners. Again, that's typical in this class of projector. For normal viewing I left the Sharpness control on it's default setting. I do spend a lot of time playing with advanced "detail enhancement" features typically found on more expensive projectors (I think the Epson 5030UB at about $2299, is the least expensive with these types of advanced image manipulation. Despite the always present minor mis-alignment of panels, and digital correction applied to that, the Epson with it's Super-Resolution, as they call it, will produce what I call a seemingly sharper image. Along with that tends to come a slight hardening of the image, so there's always trade-offs. I mention this because people are more about "perceived" sharpness" than the technical side of it.
Bottom line on the HT4050's sharpness is that it's what I expect from a $1000 - $2000 single chip DLP projector, and that's a good thing, but I do not find it to be exceptional in this regard, although I will credit it with holding sharpness better from center of the screen to the corners, than most of the lower cost projectors out there.
HT4050 Audible Noise
The HT4050 is not particularly quiet, but then rarely is that true for smaller DLP projectors. Mind you many of the DLP projectors that are physically a lot smaller than this one, are even noisier.
On paper, Optoma claims 33 db at full power, 29 db in Eco mode. That seems about right, relative to other projectors claims. 29 is hardly quiet, however, and is still enough to bother those more "noise adverse" than I. The 33db number at full power is typical in the price range, and also, I should note about the same as the Epson mentioned above in sharpness, which is a projector that sells for about 50% more (although I judge the Epson (which claims 28db in Eco, to be more like 2-3 db quieter) - I have them both here, and have switched back and forth.
I've been using the Smart Eco mode for most of my viewing, which, best I can tell, is really full power, with dynamic lamp dimming added for efficiency and a slight improvement in black level performance.
When in that mode, if the audio accompanying what I am watching is very soft, or completely quiet for a few seconds, I must report two things, you might notice that the sound has a modest high pitched whine to it (more noticeable the general air moving component). What makes it more noticeable is that it varies while you are watching. That, btw is not uncommon these days.
Is this a problem? For the seriously noise adverse, yes, but for them, very few projectors even in eco mode are satisfactory. Fortunately you and I are probably not part of that small group.
I find the whine component to the sound to be the greater issue, but it's when its varying that it is most likely to be noticed.
Bottom line on audible noise: The projector is competitive, and definitely significantly quieter than an number of competitors at and below its price, but still consider it "average." I'm certainly not going to call it quiet when there are some projectors within $1000 that may be as much as 5-7 db quieter. And that's a whole lot of difference.
Personally, I don't have a problem with the HT4050's noise levels, although if it was 2-3db quieter, that would be a worthwhile improvement. That Epson 5030UB I keep mentioning, hangs around here more or less permanently so I have a "reference" for doing comparisons. As I indicated above I find it to be just a tad quieter, and I watch that one a lot, more than 1000 hours in the last year, without bitching to myself about it being too noisy.
CFI aka Motion Enhancer. When engaging creative frame interpolation which BenQ calls Motion Enhancer, there is always some noise generated and visible as new frames are created and inserted. That noise generally surrounds the fast moving objects moving across the screen from one frame to the next.
Image noise there was pretty low - good in the low setting. Personally for sports viewing however I found that Middle was my preferred setting (I used Low sometimes as well). In Middle, there was more such noise than I prefer, but, this is a good trade-off for having the smooth motion, especially on sports. I'd hate this much image noise around fast moving objects if I was watching a movie, but then I'm fundamentally opposed to using any CFI for movie viewing because it changes the "director's intent" - that is, the feel of the filming. With CFI you get that "soap opera effect". It's your call on this. Personally I consider CFI to be a nice option, but something that pretty much everyone can live without, so I recommend you don't worry about the image noise associated with it.