Optics

Field of view, focal length, sensor size and working distance are one relationship. Fix three and the fourth is decided — which is why the lens cannot be chosen after the sensor and the mounting.

For more on organizing work around technical projects, read read more.

Field of view, focal length and distance — the geometry, and why the inch fraction in a sensor name is not a dimension.

Working out the lens you need — five steps from the installation to a part number, with a worked example that fails and explains why that is useful.

Depth of field and where it bites — a finer sensor has less of it, and the failure it produces is intermittent and looks like an algorithm problem.

For additional industry context, see All About Circuits.

Aperture, light and the trade — one setting controls light, depth of field and resolving power, and the three want different values.

IR cut filters and why they exist — silicon sees past visible light, and bench testing under fluorescent lamps hides the whole problem.

Distortion and when it matters — a geometry error rather than a loss of sharpness, harmless for detection and disqualifying for measurement.

Focus, fixing it and losing it — fixed, adjustable and automatic, and the ways a set focus is lost including somebody turning a ring.

Cleanliness and what a fingerprint costs — contamination reduces contrast long before it obscures anything, and looks like a flat image rather than like dirt.

• Aperture, Light and the Trade

  One setting controls light, depth of field and resolving power at once, and the three do not want the same value.

• Cleanliness and What a Fingerprint Costs

  Contamination reduces contrast before it obscures anything. Where it collects, what it does, and how to clean without damage.

• Depth of Field and Where It Bites

  The zone that is acceptably sharp, what widens it, and why a close-up inspection system has less of it than anybody expects.

• Distortion and When It Matters

  Straight lines that photograph as curves. What causes it, when it is entirely harmless, and what correcting it costs.

• Field of View, Focal Length and Distance

  One relationship with three terms. Fix any two and the third is decided, which is why the lens is not a separate choice.

• Focus, Fixing It and Losing It

  Fixed, adjustable and automatic focus, what each costs in reliability, and the ways a set focus drifts in service.

• IR Cut Filters and Why They Exist

  Silicon sees beyond visible light. What that does to an image, what each filter option is for, and when to remove it deliberately.

• Working Out the Lens You Need

  Five steps from the installation geometry to a part number, and the two places the calculation usually goes wrong.