Read the explanation
Field of view depends on physical focal length and the chosen sensor dimension. Use the page’s full frame width of thirty six millimeters. The source horizontal angle is two times arctangent of sensor width divided by twice focal length, converted to degrees. At one hundred millimeters focal length the horizontal field is about twenty point four one degrees. The graph uses physical focal length, not a crop-equivalent shortcut. Increase physical focal length from one hundred to four hundred millimeters with the same sensor. The marker follows the exact arctangent field-angle expression. Longer focal length narrows the angle. The axes remain fixed, so the curve is quantitatively comparable throughout the sweep. This is ideal optical geometry before telemetry rounding, not a measured photograph or a lens-performance recommendation. At four hundred millimeters the horizontal field is about five point one five degrees. Quadrupling focal length makes the field roughly one quarter, but the exact relationship uses arctangent rather than a strict reciprocal. The sensor dimensions remain unchanged. This calculation does not include lens distortion, focus breathing or a calibrated wildlife image. Keep the page’s full frame pixel pitch of five point nine micrometers. Its angular sampling formula is two hundred six point two six five times pixel pitch divided by physical focal length. At one hundred millimeters, this is about twelve point one seven arcseconds per pixel. Angular sampling is a geometric scale, not by itself a promise of resolved detail. Increase focal length from one hundred to four hundred millimeters while holding pixel pitch fixed. The marker follows an exact reciprocal curve in the source expression. Quadrupling focal length reduces angular size per pixel by four. This distinct graph uses arcseconds per pixel on its vertical axis, not the whole sensor field angle taught before. At four hundred millimeters, sampling is about three point zero four arcseconds per pixel. Smaller angular sampling does not remove diffraction, aberrations, atmosphere, movement or sensor noise. This video explains the source’s sampling arithmetic; it does not judge equipment quality or recommend a purchase. The source estimates a five hundred fifty nanometer diffraction diameter as one point three four two times aperture f number, in micrometers. At f four, the diameter is five point three six eight micrometers. Our outline represents this diameter at ten pixels per micrometer. The gray horizontal segment represents the fixed five point nine micrometer pixel pitch on that same scale. Increase aperture f number from four to sixteen. The source diameter grows linearly from five point three six eight to twenty one point four seven two micrometers. The outline radius is half the calculated diameter, so the diagram does not confuse radius and diameter. The pixel-pitch reference stays fixed. This is an explanatory diameter outline, not a rendered diffraction intensity profile or a simulated photograph. At f sixteen, the source diameter is four times its f four value and larger than the fixed pixel pitch. This ideal wavelength-specific comparison does not establish a universal sharpness threshold. The page’s exposure suggestions and target drawings are separate heuristics. All three scenes use the actual source formulas and preserve the original interactive tool.