It actually turns out that the ratio number that halves the light is 11. Standard apertures (f/Stops)īut this doesn’t mean that if you have set f/16 then f/8 would be twice the light amount let through. So different focal lengths will need different aperture areas (sizes) to pass through the same amount of light in a given unit of time. In other words the relationship of the area of the aperture opening to allow light through is the determining factor in exposure.
#F STOP BLOG FULL#
The numbers you see/use are calculated so that a doubling or halving of light passing through the aperture (iris) occurs as you move “one full stop” in the appropriate direction.
a 100mm focal length has it’s stop (aperture) set to a size of 20mm – that means the f/stop number is 5, but if the aperture size was just 4mm then the f/stop number is 25! (I used easy numbers to avoid fractions of a ratio).
Many beginners (and not a few professionals) have a hard time reconciling that a small f/stop actually means a wide aperture and vice versa, that the big f/stop numbers mean a smaller aperture size (hole).Īll is revealed when you discover that the f/stop number is the ratio result of focal length of lens / aperture size (Diameter). Another bit of paradoxical photography terminology is the numbering of f/stops (Aperture). What are they talking about?įollowing on from the previous post about the Color Temperature and why it seems to be a paradox. Photographers are always going on about “What f/stop did you give it?” This may also be expressed as: f-number, focal ratio, f-ratio, or relative aperture.
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