Definition:
Depth of field is the distance range over which the imaging resolution of the Camera Monitor System consistently meets the regulatory thresholds for vehicles at various object distances, ensuring the driver can clearly identify objects behind. Unlike photographic depth of field, CMS depth of field is quantitatively determined via MTF10, focusing primarily on whether the resolution meets the requirements rather than the extent of the sharp region.

Metrics:
The CMS shall enable the driver to observe the object space and have sufficient resolution to perceive the displayed content within the relevant range to identify details.
When the test distance is 10 m (representing infinity) or 6 m (intermediate distance), the CMS resolution shall meet:
$$MTF10_{(1:1)} \geq 0,9^*MTF10_{MIN(1:1)} \left[ \text{LW/PH} \right]\tag{1}$$

When the test distance is 4 m (close distance), the CMS resolution shall meet:
$$MTF10_{(1:1)} \geq \frac{1}{2} MTF10_{MIN(1:1)} \left[ \text{LW/PH} \right]]\tag{2}$$

Calculation Principles:
Horizontal Resolution:
$$MTF10_{\text{MIN}(1:1)/\text{hor}} = \left( \frac{W_{\text{monitor}/\text{hor}}}{W_{\text{monitor}/\text{hor}/\text{min}}} \right) \cdot M_{\text{mirror}/\text{avg}} \cdot \alpha_{\text{mirror}/\text{hor}/\text{min}} \cdot V_{\text{eye}/\text{min}} \cdot 60\,\frac{\text{arcmin}}{^\circ}\tag{3}$$

Vertical Resolution:
$$MTF10_{\text{MIN}(1:1)/\text{ver}} = \left( \frac{H_{\text{monitor}/\text{ver}}}{H_{\text{monitor}/\text{ver}/\text{min}}} \right) \cdot M_{\text{mirror}/\text{avg}} \cdot \alpha_{\text{mirror}/\text{ver}/\text{min}} \cdot V_{\text{eye}/\text{min}} \cdot 60\,\frac{\text{arcmin}}{^\circ}\tag{4}$$ $ \text{MTF10}_{\text{MIN}(1:1)/\text{hor}}$ is the MTF10 for displaying the minimum horizontal field of view assuming a monitor aspect ratio of 1:1;
$ \text{MTF10}_{\text{MIN}(1:1)/\text{ver}} $ is the MTF10 for displaying the minimum vertical field of view assuming a monitor aspect ratio of 1:1;
\( \text{MTF10}_{(1:1)/\text{hor}} \) is the horizontal spatial frequency converted to a monitor with an aspect ratio of \((1:1)\) after the standard test procedure, where $H'_{\text{monitor/ver}} = W_{\text{monitor/hor}}$ (C=A);
\( \text{MTF10}_{(1:1)/\text{ver}} \) is the vertical spatial frequency converted to a monitor with an aspect ratio of \((1:1)\) after the standard test procedure, i.e., $W'_{\text{monitor/hor}} = H_{\text{monitor/ver}}$ (C=B);
\( \alpha_{\text{monitor/hor}} \) is the horizontal field of view displayed on the defined horizontal dimension of the monitor;
\( \alpha_{\text{monitor/ver}} \) is the vertical field of view displayed on the defined vertical dimension of the monitor;
\( M_{\text{mirror/avg}} \) is the average magnification factor of the monitor;
\( H_{\text{monitor/ver}} \) is the defined vertical dimension of the monitor;
\( W_{\text{monitor/hor}} \) is the defined horizontal dimension of the monitor;
\( H_{\text{monitor/ver/min}} \) is the minimum vertical height required for the vertical field of view on the monitor;
\( W_{\text{monitor/hor/min}} \) is the minimum (required) horizontal width for the horizontal field of view displayed on the monitor;
\( V_{\text{eye}} \) is the human visual acuity; \( V_{\text{eye/min}} \) is the minimum allowable visual acuity;

Test Method:
Environment Setup:
Camera Side:
(1) Adjust the Device Under Test (DUT) camera so that its optical axis is perpendicular to the test chart and the chart is centered in the image. The chart or the camera can be rotated so that the chart lines appear vertical on the monitor when measuring horizontal resolution, and horizontal on the monitor when measuring vertical resolution.
(2) Adjust the relative distance between the camera and the test chart, and capture images at 4 m, 6 m, and 10 m (for wide-angle mirrors replacing those with a radius of curvature r ≤ 400 mm, the measurement at 10 m may be omitted); if the focal length is less than 6 m, the distance d from the camera entrance pupil to the chart shall be less than or equal to 6 m;

Screen Side:
(1) Adjust the display screen and the luminance meter (acting as the capturing camera) so that the luminance meter is aimed at the center of the monitor;
(2) Set the relevant parameters of the luminance meter to ensure the monitor image is neither overexposed nor underexposed;
(3) Use the luminance meter to capture the image displayed in the monitor area.

Result Analysis:
Based on the test samples, calculate $MTF10_{\text{MIN}(1:1)/\text{hor}}$ and $MTF10_{\text{MIN}(1:1)/\text{ver}}$ according to Equations (3) and (4). Measure the width $W'_{\text{chart}}$ of the nine lines at chart position 1 on the monitor (refer to h in the figure for the width);
Then calculate the spatial frequency at position 1: $$K_{\text{hor}} = \frac{W_{\text{monitor/hor}}}{W'_{\text{chart/hor}}} \cdot 9\tag{5}$$ $$K_{\text{ver}} = \frac{W_{\text{monitor/ver}}}{W'_{\text{chart/ver}}} \cdot 9\tag{6}$$

Then calculate the scaling factor P to verify the MTF requirements: $$P_{\text{hor}} = \frac{MTF10_{\text{MIN}(1:1)/\text{hor}}}{K_{\text{hor}}}\tag{7}$$ $$P_{\text{hor}} = \frac{MTF10_{\text{MIN}(1:1)/\text{hor}}}{K_{\text{hor}}}\tag{8}$$ Visual acceptance level reference: The effects are classified into 3 levels:
Clearly distinguishable: After capturing the parallel line pair chart, the displayed image can be clearly distinguished (corresponding to categories (a)-(b));
Barely distinguishable: After capturing the parallel line pair chart, the displayed image can only be barely distinguished (corresponding to categories ©-(d));
Indistinguishable: After capturing the parallel line pair chart, the displayed image cannot be distinguished and is not applicable for CMS (corresponding to categories (e)-(f)).

Find the line pair value at the chart position corresponding to the P value, and visually verify that all line pairs can be observed and distinguished, indicating that the CMS meets the standard requirements.