Aperture / f-stop question


TPF Noob!
Oct 31, 2007
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What I'm wondering about all the time is following:

When we talk about th f-stops, we mean the full-stops....!?
means f/2.8 - f/4 - f/5.6 - f/8 - f/etc.....

But what is with all the f/# in between...like f/3.2 etc ???
Are those "half-stops" ?
does everybody prefer using the full-stops instead of the ones in between?

I'd be thankful if there's anyone that could explain that to me...

Most modern cameras & lenses have adjustments in half or 1/3 stops...so yes, that's where some of those odd F numbers come from.
They're half-stops (and some third/stops) but I tend to think in full stops... and then use whatever makes sense. For instance... If I'm using my 50mm, and want to a decent amount of DOF... but don't want to shoot under 1/60th, I'll keep adjusting my aperture till my light meter says "good enough." If that's some odd-number stop, so be it.
well usually we estimate "should be 1 stop brighter" or something...
If it's really more like 2/3...then that's fine too.

They are called 1/3 and 1/2 stops...yes.
The "F" stands for "focal length" and that "/" really means "divided by". An F-stop is a fraction that represents the diameter of an aperture.

Example, on a 100mm lens, at an aperture of of F/1.4 the opening of the lens would be 71.4mm. (100mm / 1.4 = 71.428mm)

Additional info... every time you stop down, you cut the available light coming into the lens by half. Thats why larger numbers need more light, and smaller numbers require less. Using smaller numbers, you are in effect having larger lens openings and more light comes in to expose the film or fall upon the sensor.

More modern cameras can go "in between" full stops. Sometimes in 1/3rds or in 1/2's for even more abilty to meter light properly to the film or sensor.

My preference is to match the setting to the needs. Often it falls in between full stops, so thats an advantage in terms of getting that picture closer to a "proper" exposure. As far as
"proper exposure", well thats where the book understanding exposure will best help those that are lost in that area. :wink:
very good explanation JerryPH...this concept is a hard one to grasp, but you put it into words that I can understand...thank you

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