Low Lamp Mode. Eco mode lowers brightness by about 33% compared with the full power setting.
Zoom Lens Light Loss. The 1.3x zoom lens drops brightness by only about 12% in the full telephoto setting, which is little enough to ignore in most cases when deciding how far to place the projector from the screen for a given size image.
Color Brightness. The UHD51A performs well on color brightness tests. Even in the Bright mode the color output measures 80% of white, and in all other presets it exceeds 85%.
Brightness Uniformity. The measured brightness uniformity for the UHD51A is 63% at the wide-angle end of the lens and 68% at the telephoto end--a little low for a home theater projector in this price range. With a solid white test image, there's minor visible fading on the left and rightmost 5% to 10%. Those who are particularly aware of low uniformity may find it bothersome. Others will never notice it because the brightness change isn't obvious and it is on the edges of the image which you rarely focus on.
Video Optimized Lumens (SDR). Even with default settings, color in Cinema mode is well within a realistic range, although moderate tweaking of Color Matching settings gives more accurate color. The more important issue with the defaults is low contrast and lack of three dimensionality, which is easily fixed by adjusting brightness and contrast. After adjustments, black is suitably dark; contrast, shadow detail, and three dimensionality are all excellent; and brightness is unchanged.
The measured 1,153 lumens with optimized settings is enough to fill a 175" 1.3-gain screen in a dark room. Eco mode's 769 lumens is enough for a 145" screen, and it gives you the flexibility to move to Bright power mode as the lamp loses brightness with age. For rooms with ambient light, the video optimized settings with Bright power mode can still light up a 110" screen.
Color Preset Mode Performance. The UHD51A's Cinema mode is its second brightest mode. Game and Reference modes both deliver a touch lower brightness, with color that's similar in hue but less saturated. HDR Sim is just a little green shifted, but nowhere near as much as the brightest mode.
As with most projectors' brightest modes--Bright mode has an obvious green bias. Unlike many DLP models, changing the Brilliant Color setting to 1 (which is off) from the default 10 doesn't improve color accuracy enough to matter. If you need the extra brightness to combat ambient light you may be willing to use it occasionally if you don't mind the green tint.
Frame Interpolation. The UHD51A's FI offers three settings besides Off. The factory default setting is Low, which smooths motion enough to notice while still showing a bit of judder in pans or an object moving across the field of view. However, there's little-to-no digital video effect, which leaves nothing to gain from turning it off. Unlike the maximum setting in many projectors, High doesn't smooth motion entirely, but it also adds only a minor digital video effect. You might prefer a more aggressive version of FI for live and recorded video, but this more subtle version is better for film.
4K HDR Performance. Unlike some 4K projectors, the UHD51A handles the switch from SDR to HDR input and back again fully automatically. When it detects HDR, it switches to HDR color mode as the only choice. When it detects SDR, it switches back to whatever color mode it was previously set to.
The HDR mode has four settings: Bright, Standard, Film and Detail. All four deliver a compelling picture with excellent contrast, dark blacks, and a good sense of three dimensionality. The main difference between them is that at each step from Bright to Standard to Film the image gets darker overall and shows less shadow detail separation.
3D Performance. The UHD51A is one of the few 4K UHD projectors that offers 3D at 1080p, which alone makes it a strong contender if you have a library of 3D discs. It handles 3D nicely, with no crosstalk in my tests and just the typical hint of 3D-related motion artifacts. You can adjust picture controls in 3D mode, but even with the defaults it delivers a highly watchable picture. As with any projector, 3D isn't as bright as any of the 2D modes, but the brightness drops far less in 3D than with most projectors. Unlike most Optoma models the UHD51A supports DLP-Link glasses only.
As an aside, the UHD51A didn't always recognize 3D input from Verizon FiOS. When that happens, you have to switch the video source back to 2D material, set the projector to 3D, and then switch the source back to the 3D material you want to watch. Optoma says it is looking into this issue.
Rainbow artifacts. As with most DLP projectors, the UHD51A can show rainbow artifacts. However, they don't show as often as with many other models. Even in a contrasty black and white clip I saw very few, and I saw even fewer with color clips. If you don't see these artifacts easily or don't find them bothersome, they won't be an issue. If you're sensitive to them or don't know if you are, try to buy the projector from a dealer that allows easy returns so you can test it out for yourself.
Onboard audio. Should you need to use the UHD51A's onboard audio instead of an external sound system, the two 5-watt stereo speakers deliver good sound quality and enough volume for a small to mid-size room.
Fan noise. The UHD51A is notably quiet, rated at 28 dB in full power mode and 25 dB in Eco mode. In a small room you can hear the fan in quiet moments, but it is low pitched, steady white noise that tends to fade into the background.
Optoma recommends using High Altitude mode at 5,000 feet and above. In Eco mode it is still quiet enough, but in full power mode it is loud enough to consider using some sound deadening material around it.
Input lag. With FI off, the projector measures a minimum of 68 to 70 ms lag depending on the color mode.
Connection Panel Inputs:
Throw Distance. The UHD51A's 1.3x zoom lens allows a throw distance for a 120" 16:9 image from about 10.5 to 13.8 feet. You can use the Optoma UHD51A Projection Calculator to find the throw distance range for the image size you want.
Lens offset. With the UHD51A right side up, the lens shift allows the bottom edge of the image to be anywhere from even with the centerline of the lens to as much as 14% of the image height above the centerline. This is an ideal range for setup on a low table or inverted in a ceiling mount.
There is no keystone adjustment to square off the image, which means you should avoid any situation that forces you to tilt the projector up or down to hit the screen. This effectively rules out options like putting it on a high shelf behind the seats, which will usually force you to tilt the projector downward.
The Optoma UHD51A's most eye-catching feature is its unique (for the moment) support for Alexa, but that's not the best reason to buy it. Voice commands are currently limited to turning the projector on and off, adjusting volume, changing the input source, and controlling the USB media player. For all other settings, you still need to use the remote or controls on the projector itself. Sorely missing, but promised to be added shortly, are commands to change the Display Mode, FI setting, and color mode.
It is hard to argue that these voice command features, even with the promised additions, are by themselves worth the $300 higher cost for the UHD51A compared with the UHD50. However the other additions--FI, 3D, built-in USB media player, support for mobile devices, and boosting the warranty to two years--add enough value to easily justify the increased price.
The Optoma UHD50 has a slightly faster input lag at 57 ms, but it isn't enough to make any practical difference. And although our UHD51A measured about 85% as bright as our UHD50 in their Bright modes, it measured 94% as bright for Cinema mode, which is what you'll want for best picture quality. And the difference is within the range of expected variation from one unit to another in any case.
Most important, the Optoma UHD51A is easily bright enough even in ECO mode to light up a 140" 1.3-gain screen in a dark room and produce a compelling picture in SDR or HDR. And it even offers 3D for 1080p, which the UHD50 and most other 4K projectors don't. That's more than enough to make it an excellent value at $1,699.
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