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I had wanted a 240hz monitor to gain an advantage (reduced input lag) over others in fps games and I since I constantly read from online forums and heard from youtube videos that all 240hz and 144hz tn panels come from the same korean manufacturer, I figured they would all have the same quick input lag regardless of price and went ahead and purchased the cheapest 240hz I could find. The acer KG251Q is significantly cheaper at approximately $370 AUD versus your flagship benq xl2540. The colours are surprisingly better, and the clarity when in motion is a step up from my previous benq xl2411z 144hz monitor. But for some reason when playing counterstrike I noticed I would be killed before I had time to react, this did not happen when playing with the 144hz. Up until a few days ago I thought I was losing my mind until I did some comparison tests taking shots with a sony A7 camera at a shutter speed of 1/8000. I think my testing methodology is correct, all I did was clone the benq 144hz in nvidia control panel and then took photos of both monitors with a displayed stopwatch side by side. I also tested cloning the 240hz (idk if that matters). Benq 144hz on left, cheap acer 240hz on the right. I did not hand pick the images honestly chose 3 random ones sometimes it would have the exact same input lag as the benq but no lie majority of the time it would show these massive 50ms variances.

I have read some bad things about this monitor after I had already purchased it, so I just want to raise awareness and let people know to spend a bit more and not make the mistake like I did.

I also would like to know which 240hz monitor has the lowest input lag as I will be purchasing a new one and I want that leading edge. Please provide articles, thanks!

Span your displays and find a stopwatch that you can split on both monitors simultaneously, it is more proper techinque to compare them side by side. At your pictures, right display is around 60ms behind the left one, but it doesnt neccessary means that input lag of the right display is 60ms worse then left.
Display cloning adds its own delay. Also, since you are measuring in windows browser, both displays are running with vsync on, also having different refresh rate, and vsync is definitely adds its delay to the whole chain.
That's why generally any browser-based timers are not ideal to measure and compare input lag. There is a tool SMTT 2.0 that can run in fullscreen exclusive mode with Vsync off.

k2viper wrote:Span your displays and find a stopwatch that you can split on both monitors simultaneously, it is more proper techinque to compare them side by side. At your pictures, right display is around 60ms behind the left one, but it doesnt neccessary means that input lag of the right display is 60ms worse then left.
Display cloning adds its own delay. Also, since you are measuring in windows browser, both displays are running with vsync on, also having different refresh rate, and vsync is definitely adds its delay to the whole chain.
That's why generally any browser-based timers are not ideal to measure and compare input lag. There is a tool SMTT 2.0 that can run in fullscreen exclusive mode with Vsync off.

Thanks for your input I'll redo the test sometime today and post here. I still think the 144hz will be at least slightly faster.

Friard wrote:

k2viper wrote:Span your displays and find a stopwatch that you can split on both monitors simultaneously, it is more proper techinque to compare them side by side. At your pictures, right display is around 60ms behind the left one, but it doesnt neccessary means that input lag of the right display is 60ms worse then left.
Display cloning adds its own delay. Also, since you are measuring in windows browser, both displays are running with vsync on, also having different refresh rate, and vsync is definitely adds its delay to the whole chain.
That's why generally any browser-based timers are not ideal to measure and compare input lag. There is a tool SMTT 2.0 that can run in fullscreen exclusive mode with Vsync off.

Thanks for your input I'll redo the test sometime today and post here. I still think the 144hz will be at least slightly faster.

Any free applications like smtt?

THIS!!!

I bought the exact same monitor just yesterday, immediately tried some games, and it was noticeably smoother than my previous 144Hz monitor (Acer XF240H) however I thought fast movements like flick shots felt slightly off. First I thought it's because of the "slow motion" feeling that a higher refresh rate gives, but then I did a lot of testing, and I can confirm that this monitor has more input lag, at least compared to my old one. My exact model is KG251QDbmiipx.

Here's a short video I made that illustrates the issue.
Please note that I have repeated these tests dozens of times in the past two days, and gotten the same results every time, so I'm not jumping to conclusions from this one attempt.



Simple test, I bump my mouse with another object (just so it's easier to see the exact frame when it starts moving), then count the frames between the mouse moving and the screen changing. I can only film at 240fps on my phone, but even with that, my old monitor pretty consistently takes 2 frames (about 8ms) from mouse to pixel, while the new 240Hz one takes 3 to 4 frames (about 12-16ms).

My mouse is set to 1000Hz polling rate at 800dpi, I ran CS:GO in exclusive full screen on each monitor (at 144Hz and 240Hz obviously), the game was running around 400fps.

I tried pretty much everything I could with OSD settings, custom resolutions, nothing helped.

This is really disappointing, since the monitor otherwise is pretty good for the price, the panel has surprisingly good saturation, contrast, brightness, and even viewing angles for a TN (although it could use a calibration), but I'm not sure if I want to deal with this kind of input lag in competitive games. Again, I could tell that something was up with this, just based on feel, even before testing with slow motion, so it would probably affect my gameplay. I'm really disappointed in this

Fully agree on "That's why generally any browser-based timers are not ideal to measure and compare input lag. There is a tool SMTT 2.0 that can run in fullscreen exclusive mode with Vsync off."
Thanks for posting your experience with that monitor.

I guess I should also try SMTT 2.0. I've been only doing these in-game tests that I showed.

EDIT:
Nevermind, you can't get it anymore

So I did another test with gun fire / clicking. CS:GO running at around 400fps, exclusive full screen at 144Hz and 240Hz, and I synced up the exact frames where the mouse button gets pressed with every pair of clips. Mouse is set to 1000Hz polling.

The 240Hz Acer only comes close at best to my older 144Hz. Sometimes it's almost on par, but other times it's a lot slower. The variance probably comes from the fact that I only have 240fps slow mo. I would need like 1000fps for more consistency. But even then, I think it's pretty clear, this monitor isn't the best if you're going for competitive play. Those few extra milliseconds aren't acceptable for a monitor aimed at competitive esports, which 240Hz obviously is

The Acer KG251Q can only do up to 75Hz.

Are you sure you're not mixing up with the Acer XF270HA?

Can you test http://www.testufo.com/frameskipping to make sure that it's displaying 240 unique refresh cycles per second? We've occasionally run into frameskipping issues on certain models of 240Hz monitors -- and that adds irregular input lag when refresh cycles are skipped.

Chief Blur Buster wrote:The Acer KG251Q can only do up to 75Hz.

Are you sure you're not mixing up with the Acer XF270HA?

Can you test http://www.testufo.com/frameskipping to make sure that it's displaying 240 unique refresh cycles per second? We've occasionally run into frameskipping issues on certain models of 240Hz monitors -- and that adds irregular input lag when refresh cycles are skipped.

Yes I have tested it with that tool, and also and the image is noticeably smoother than my 144Hz monitor, it is a 240Hz panel.
The exact model's page is here. It's hard to find because I the 240Hz one is only sold in some regions, and the model names are really confusing. It's the "D" in the model name after the "Q" that differentiates this from the other models, some of which are 75Hz.

EDIT:
Here's my picture, just to make sure.