How do you choose circle of confusion for depth of field on a 16K line-scan camera?
Asked 1/10/2024
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Can standard depth-of-field formulas be used with a line-scan camera? I have a 16K CMOS line-scan sensor with 16,384 pixels at 5 µm pitch (about 81.9 mm wide). How should I determine an appropriate circle of confusion for DOF calculations: should I base it on pixel size, sensor diagonal, or intended output/viewing conditions?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
2y ago
2 Answers
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The circle of confusion is what you accept as tolerable blur.
In the olden days of 35mm film photography, a common convention was to accept a 30µm diameter as "sharp enough". Translating this into the digital world, this roughly corresponds to a 1 megapixel resolution.
The DoF calculations have nothing to do with the medium that captures the image, only with the optical system that produces the image, and your acceptable circle of confusion. So yes, generic DoF formulas can be used for linescan sensors as well.
So, if you need the full resolution of your linescan camera (and your optics are good enough!), then use the single-pixel size of 5µm for your DoF calculations. If you can e.g. accept a degradation to effectively 4000 pixels (blur size = 4 pixels), then use 20µm.
Originally by user79539. Source · Licensed CC BY-SA 4.0
user79539
2y ago
0
Generated from our catalog & community — verify before relying on it.
Yes. Standard DOF formulas still apply to a line-scan camera because DOF is determined by the optics and by the blur size you consider acceptable, not by whether the sensor is area-scan or line-scan.
The circle of confusion (CoC) is not a fixed property of the camera; it is a chosen tolerance.
Practical ways to choose it:
- If you want to preserve full sensor resolution, use about one pixel as the CoC: for your sensor, 5 µm.
- If a little blur is acceptable, use a multiple of the pixel size. For example, 4 pixels would be 20 µm.
- If you want a conventional viewing-based CoC, a common rule is sensor diagonal / 1500.
With a width of 16,384 × 5 µm = 81.92 mm, the exact diagonal depends on the sensor height, so you’d need the full sensor dimensions to use the diagonal/1500 rule precisely.
So: yes, use normal DOF formulas, and choose the CoC based on your required final sharpness. For maximum measurable detail, start with 5 µm.
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