Which f-stop is the sharpest? GFX 50S Diffraction Test

How do you determine the sharpest f-stop for your camera and lens? Is diffraction more impactful in infrared light than visible light? In this video, I will test the sharpest f-stop on a Fujifilm GFX 50S full spectrum conversion at each aperture with multiple infrared filters, 550 nanometers, 590 nm, 720 nm, 830 nm, 850 nm, IR Chrome, and a hot mirror filter. I’ll share the results and my observations.

Results

Fujifilm GFX 50S full spectrum conversion, GF 45 mm f/2.8 lens

Filter Wavelength Sharpest f-stop
STC Optics UV/IR (hot mirror) visible light f/11
Kolari Vision IR Chrome dual-bandpass f/11
Full spectrum n/a f/8
Kolari Vision 550 550 nm f/8
STC Optics IRP 590 590 nm f/8
STC Optics IRP 720 720 nm f/8
Hoya R72 720nm f/5.6 & f/8
B+W 093 830 nm f/5.6
STC Optics IRP 850 850 nm f/5.6

Recommendations

Filter Adjustment from sharpest visible light f-stop
Hot mirror, IR/UV cut, IR Chrome Use sharpest visible light f-stop
550 to 720 nm 1-stop lower
800 nm and higher 2-stops lower
  • Lower f-stops: Sharpness is reduced with f-stops lower than the sharpest f-stop due to less depth of field. The loss of sharpness is minimal. Lower f-stops will not substantially impact sharpness. Use lower f-stops to reduce the depth of field.
  • Higher f-stops: Sharpness is reduced with f-stops higher than the sharpest f-stop due to increased visible diffraction. The loss of sharpness is dramatic. Avoid these higher f-stops unless you are explicitly looking for a soft effect, want to create a starburst effect, or are willing to trade reduced sharpness for greater depth of field.

Previous Diffraction Article/Video on Fujifilm X-T20 (APS-C)

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