Depth of Focus
Introduction
Depth of Focus describes the range of distances where an object appears in focus. Objects outside this range will appear blurry.
In this article, we will explain the basic principles of Depth of Focus and how to apply these principles to Zivid cameras.
What is focus?
Focus is determined by the Circle of Confusion (CoC). The CoC is the radius, or area, covered by light from a point as it hits the imaging sensor after passing through the camera lens. An object is out of focus when the CoC is large enough to cover more than one pixel, causing signal loss and noise. When the aperture is sufficiently large, objects too close to the lens will be focused in front of the sensor, and objects too far will be focused behind the sensor, both resulting in blur. See the illustration below.
Depth of Field
The Depth of Field is the range of distances where an object is in focus. The boundaries are defined by the near focus distance (\(d_{near}\)) and the far focus distance (\(d_{far}\)). Outside these boundaries, the CoC increases, causing light to spread into neighboring pixels.
The angles at which the lens refracts the light rays grow with the aperture size. For Zivid 3D cameras, a large aperture can cause objects to lose focus, reducing the Signal-to-Noise Ratio (SNR) and making the point cloud noisier. Therefore, selecting the appropriate aperture for the camera’s working distance is crucial for optimal image quality.
How does focus affect my point cloud?
As the image gets more out of focus, artifacts such as noise and Contrast Distortion will increase. When we speak about noise, we are talking about the point precision of the point cloud. This means that the capture-to-capture variations of a given pixel will increase and that the pixel-to-pixel variation within for a given capture will increase. It is important to be aware that a slight increase in noise may still be acceptable. Slight increases in noise may be acceptable depending on the processing algorithm used. Therefore, an unfocused image can still be acceptable in many cases.
Note
Zivid cameras are robust against defocus!
It is also important to note that only the out-of-focus regions of the image will be affected. Consider the camera’s working distance for the given application to achieve good point clouds with optimal precision.
Depth of Focus for Zivid Cameras
The table below shows the Depth of Focus for Zivid cameras.
Zivid 2+ M130/MR130 |
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|---|---|---|---|---|---|---|---|---|---|
\(f\) -number |
\(f/2\) |
\(f/2.8\) |
\(f/4\) |
\(f/5.6\) |
\(f/8\) |
\(f/11\) |
\(f/16\) |
\(f/22\) |
\(f/32\) |
Stops |
+3 |
+2 |
+1 |
0 |
-1 |
-2 |
-3 |
-4 |
-5 |
Focus, near (mm) |
1115 |
1055 |
975 |
885 |
780 |
680 |
560 |
460 |
355 |
Focus, far (mm) |
1560 |
1695 |
1945 |
2430 |
3880 |
15120 |
Inf [1] |
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Depth of Field (mm) |
445 |
640 |
970 |
1545 |
3095 |
14440 |
Inf [1] |
Inf [1] |
Inf [1] |
Zivid 2+ L110/LR110 |
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|---|---|---|---|---|---|---|---|---|---|
\(f\) -number |
\(f/2\) |
\(f/2.8\) |
\(f/4\) |
\(f/5.6\) |
\(f/8\) |
\(f/11\) |
\(f/16\) |
\(f/22\) |
\(f/32\) |
Stops |
+3 |
+2 |
+1 |
0 |
-1 |
-2 |
-3 |
-4 |
-5 |
Focus, near (mm) |
800 |
720 |
630 |
535 |
440 |
360 |
275 |
215 |
155 |
Focus, far (mm) |
1769 |
2310 |
4375 |
Inf [1] |
Inf [1] |
Inf [1] |
Inf [1] |
Inf [1] |
Inf [1] |
Depth of Field (mm) |
960 |
1590 |
3745 |
Inf [1] |
Inf [1] |
Inf [1] |
Inf [1] |
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Zivid 2+ M60/MR60 |
|||||||||
|---|---|---|---|---|---|---|---|---|---|
\(f\) -number |
\(f/2\) |
\(f/2.8\) |
\(f/4\) |
\(f/5.6\) |
\(f/8\) |
\(f/11\) |
\(f/16\) |
\(f/22\) |
\(f/32\) |
Stops |
+3 |
+2 |
+1 |
0 |
-1 |
-2 |
-3 |
-4 |
-5 |
Focus, near (mm) |
500 |
465 |
425 |
380 |
330 |
285 |
230 |
185 |
140 |
Focus, far (mm) |
755 |
840 |
1010 |
1390 |
3200 |
Inf [1] |
Inf [1] |
Inf [1] |
Inf [1] |
Depth of Field (mm) |
255 |
370 |
585 |
1010 |
2870 |
Inf [1] |
Inf [1] |
Inf [1] |
Inf [1] |
Zivid 2 M70 |
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|---|---|---|---|---|---|---|---|---|---|
\(f\) -number |
\(f/2\) |
\(f/2.8\) |
\(f/4\) |
\(f/5.6\) |
\(f/8\) |
\(f/11\) |
\(f/16\) |
\(f/22\) |
\(f/32\) |
Stops |
+3 |
+2 |
+1 |
0 |
-1 |
-2 |
-3 |
-4 |
-5 |
Focus, near (mm) |
530 |
480 |
420 |
370 |
300 |
250 |
190 |
150 |
110 |
Focus, far (mm) |
1040 |
1280 |
1990 |
7630 |
Inf [1] |
Inf [1] |
Inf [1] |
Inf [1] |
Inf [1] |
Depth of Field (mm) |
510 |
800 |
1570 |
7260 |
Inf [1] |
Inf [1] |
Inf [1] |
Inf [1] |
Inf [1] |
Zivid 2 L100 |
|||||||||
|---|---|---|---|---|---|---|---|---|---|
\(f\) -number |
\(f/2\) |
\(f/2.8\) |
\(f/4\) |
\(f/5.6\) |
\(f/8\) |
\(f/11\) |
\(f/16\) |
\(f/22\) |
\(f/32\) |
Stops |
+3 |
+2 |
+1 |
0 |
-1 |
-2 |
-3 |
-4 |
-5 |
Focus, near (mm) |
680 |
605 |
520 |
430 |
350 |
280 |
210 |
160 |
120 |
Focus, far (mm) |
1870 |
2870 |
14290 |
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Depth of Field (mm) |
1190 |
2260 |
13770 |
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Depth of Focus Calculator
By using Zivid’s depth of focus calculator, it is possible to find the recommended max aperture based on the working distance and acceptable blur radius. Keep in mind, getting sharp images in the region of interest is one of many things needed for optimal point cloud quality, but it is not a hard constraint. As mentioned above, Zivid 3D technology is very resilient to blur and defocus. It will still be able to provide good point clouds even if the image appears out of focus, though they can be a little noisier.