Sensor and Performance

The Razer Viper 8K is equipped with the Focus+. According to specifications, the Focus+ is capable of up to 20,000 CPI as well as a maximum tracking speed of 650 IPS, which equals 16.51 m/s. "Focus+" is Razer's name for the PAW3399, which has been co-developed by PixArt and Razer. Out of the box, five pre-defined CPI steps are available: 400, 800, 1600, 2400, and 3200.

All testing was done on the latest firmware. As such, results obtained on earlier firmware versions may differ from those presented hereafter. Unless noted otherwise, I'll exclusively test the Viper 8K at 1000 Hz on this page. This is done both to provide the full picture and establish a baseline for testing polling rates higher than 1000 Hz, which follows on the next page.

CPI Accuracy

"CPI" (short for counts per inch) describes the number of counts registered by the mouse if it is moved exactly an inch. There are several factors (firmware, mounting height of the sensor not meeting specifications, mouse feet thickness, mousing surface, among others) which may contribute to nominal CPI not matching actual CPI. It is impossible to always achieve a perfect match, but ideally, nominal and actual CPI should differ as little as possible. In this test, I'm determining whether this is the case or not. However, please keep in mind that said variance will still differ from unit to unit, so your mileage may vary.


I've restricted my testing to the four most common CPI steps, which are 400, 800, 1600, and 3200. As you can see, deviation is decently low, which is a good result overall. In order to account for the measured deviation, adjusted steps of 400, 800, 1550, and 3100 CPI have been used for testing.

Motion Delay

"Motion delay" encompasses all kinds of sensor lag. Any further sources of input delay will not be recorded in this test. The main thing I'll be looking for in this test is sensor smoothing, which describes an averaging of motion data across several capture frames in order to reduce jitter at higher CPI values, increasing motion delay along with it. The goal here is to have as little smoothing as possible. As there is no way to accurately measure motion delay absolutely, it can only be done by comparison with a control subject that has been determined to have the lowest possible motion delay. In this case, the control subject is a G403, whose 3366 has no visible smoothing across the entire CPI range. Note that the G403 is moved first and thus receives a slight head start.


First, I'm looking at two xCounts plots generated at 1600 and 20,000 CPI. To my knowledge, the Focus+ has a fully dynamic framerate, which means that these plots would be non-indicative of any potential smoothing. That having been said, for the Viper 8K, a fully dynamic framerate isn't used. What we can see, however, is SPI timing jitter being very low. This is due to Motion Sync, which synchronizes SPI communication with USB polling events.


In order to determine motion delay, I'm looking at xSum plots generated at 1600 and 20,000 CPI. The line further to the left denotes the sensor with less motion delay. As you can see, neither show any motion delay differential, which confirms that there is no smoothing across the entire CPI range.

Speed-related Accuracy Variance (SRAV)

What people typically mean when they talk about "acceleration" is speed-related accuracy variance (or short SRAV). It's not about the mouse having a set amount of inherent positive or negative acceleration, but about the cursor not traveling the same distance if the mouse is moved the same physical distance at different speeds. The easiest way to test this is by comparison with a control subject that is known to have very low SRAV, which in this case is the G403. As you can see from the plot, no displacement between the two cursor paths can be observed, which confirms that SRAV is very low.

Perfect Control Speed

Perfect Control Speed (or PCS for short) is the maximum speed up to which the mouse and its sensor can be moved without the sensor malfunctioning in any way. I've only managed to hit a measly 4.5 m/s (which is within the proclaimed PCS range), at which no sign of the sensor malfunctioning can be observed.

Polling-rate Stability

All tested polling rate settings (125 Hz, 500 Hz, and 1000 Hz) look nice and stable. Polling stability is unaffected by any RGB setting.

Paint Test

This test is used to indicate any potential issues with angle snapping (non-native straightening of linear motion) and jitter, along with any sensor lens rattle. Please note that testing was done at 8000 Hz. As you can see, no issues with angle snapping can be observed. No jitter is visible at 1600 CPI and 3200. 10,100 CPI shows some jitter, but it is still rather well-controlled given the lack of smoothing. The same goes for 20,000 CPI, which shows more jitter and ripple, but continues to be mostly under control. Lastly, there is no sensor lens movement.

Lift-off Distance

The Viper 8K offers a wider range of possible LOD adjustment than most mice. One can either set LOD to pre-defined levels of 1, 2, or 3 mm or choose to run a manual calibration. When using the 1 mm option, the sensor does not track at a height of 1 DVD (<1.2 mm). When using the 2 mm setting, the sensor does track at a height of 1 DVD, but not at a height of 2 DVDs (1.2<x<2.4 mm, x being LOD height), which doesn't change when using the 3 mm option. Additionally, Asymmetric Cut-off can be enabled, which allows for a higher lift-off distance while keeping the landing distance low. Keep in mind that LOD may vary slightly depending on the mousing surface (pad) it is being used on.

Click Latency

Most computer (and gaming) mice use mechanical switches for the buttons. Mechanical switches need debouncing in order to function as intended, which can add a delay commonly referred to as click latency. Much like recent Razer mice, the Razer Viper 8K is using optical switches for the main buttons. Optical switches do not require any debouncing, hence no delay is added. Unfortunately, this also means I'm unable to conduct my usual click latency testing. Using the less accurate and reliable "bump test" at a polling rate of 8000 Hz, I'm able to measure results that indicate a click latency roughly 1 ms lower than that of the SteelSeries Ikari, which acts as the baseline (+0.0 ms). Please keep in mind that the measured value is not the absolute click latency.