Diffraction Limit Finder

What is diffraction?

When light passes through a small aperture opening, it bends — this is diffraction. At wide apertures the opening is large relative to the wavelength of light, so diffraction is negligible. As you stop down and the aperture gets physically smaller, diffraction causes each point of light to spread into a disc on the sensor (the Airy disk). Once that disc is larger than a single pixel, diffraction starts softening the image.

Why M43 is more affected than full frame

A 20MP M43 sensor and a 20MP full-frame sensor have the same pixel count, but the M43 sensor is physically smaller (17.3 × 13mm vs 36 × 24mm). Fitting the same number of pixels into a smaller area means each pixel is smaller — around 3.3μm on M43 vs 6.0μm on full frame. The Airy disk reaches one-pixel size at a much lower f-number on M43, so diffraction becomes the limiting factor earlier.

A full-frame camera at the same resolution stays diffraction-free up to roughly f/9–10. M43 at 20MP hits the same threshold around f/5. This is why experienced M43 shooters treat f/8 as a practical ceiling for maximum sharpness, and why stopping down to f/16 on M43 noticeably softens the image in a way that f/16 on full frame does not.

How to use this in practice

• Onset is the aperture where diffraction equals one pixel's width. You will only see this softening if you pixel-peep at 100% — it is not visible in normal viewing.
• Practical limit is one stop beyond onset (Airy disk spanning two pixels). Diffraction softening is visible in large prints or on high-resolution displays at this point.
• Sweet spot is the aperture range where most lenses hit their peak — diffraction is minimal and lens aberrations are well-controlled. For most M43 shooting, f/4 to f/5.6 is the optimum.

The formula

Pixel pitch is calculated from the M43 sensor area (17.3 × 13mm = 224.9mm²) divided by the megapixel count, then square-rooted. The diffraction onset f-stop uses the Rayleigh criterion: f-number = pixel pitch ÷ (1.22 × 0.55μm), where 0.55μm is the wavelength of green light — the reference wavelength used in optical calculations because the human eye is most sensitive to it.