Aperture (F-Number)
0x829dAlso: FNumber, ApertureValue
How wide the lens opening was.
The f-number describes how wide the lens aperture was open. Confusingly, smaller numbers mean a wider opening: ƒ/1.8 lets in far more light (and blurs the background more) than ƒ/16.
EXIF stores it as a rational number. It controls both exposure and depth of field — the amount of the scene that is in focus.
Two tags hold the same fact and readers disagree about which to trust. FNumber (0x829d) stores 2.8 directly; ApertureValue (0x9202) stores the APEX logarithm of it, which is why some viewers show a stray value like ƒ/2.83. On a phone the aperture is fixed, so the figure is a property of the hardware and tells you nothing about the exposure.
Want to see this tag in your own photo? Open the EXIF Viewer and drop an image — every tag is decoded in your browser. To take this tag back out again, remove the EXIF data losslessly.