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22 votes
Accepted

Why are 1/3 stop apertures uneven numbers apart?

For f/stops, there is a precise multiplied difference of 1.122462 X intervals (cube root of √2) between all third stops. The precise third stops are actually numbers like 8.98 or 10.08. My meaning of ...
WayneF's user avatar
  • 12.9k
20 votes

Why are DSLR lenses measured in F stops instead of T stops?

Because in cinema, it's common to change lenses within a shoot while preserving identical exposure. This is rarely important in still photography (and even less so with the flexibility of digital). ...
mattdm's user avatar
  • 143k
17 votes

Why are DSLR lenses measured in F stops instead of T stops?

To add to mattdm's great answer: In addition to the added exposure precision, which is not important to photography, T-Stops are LESS precise in other ways which ARE important to still photography. ...
wedstrom's user avatar
  • 352
16 votes

Why are DSLR lenses measured in F stops instead of T stops?

F-Stops matter most when you care about knowing your composition and depth of field, T-Stops matter most when you care about knowing your exposure. Photographers want to control composition first and ...
J...'s user avatar
  • 611
13 votes

Confused about T-stop number. Does it account for crop factor?

Crop factor has nothing to do with T-stop. T-stop is strictly about light transmission which affects exposure. If a lens could be 100% transmissive the T-stop and f-number of the lens would be the ...
Michael C's user avatar
  • 175k
13 votes
Accepted

What motivated lens makers to now use 1/3 f-stops rather than say 1/4 or 1/2 stops?

Historically, the unit of exposure was a doubling or halving of the exposing energy. This is the origin of the f/stop. Initially, this adjustment was made by inserting a thin metal plate with a ...
Alan Marcus's user avatar
  • 39.2k
13 votes

Why are 1/3 stop apertures uneven numbers apart?

Whole f-numbers are an expression of the powers of the square root of two (√2). Every odd-numbered or fractional power of the square root of two is a non-integer with an endless number of places to ...
Michael C's user avatar
  • 175k
9 votes

How many extra stops do monopods offer for tele photographs?

The monopod removes three degrees of liberty: distance from ground is fixed, and roll and pitch are linked to position in space. But you are overlooking that you are no longer lifting the (...
xenoid's user avatar
  • 21.4k
8 votes

F-stop vs T-Stop - how do I quickly grasp a videographers view of the world?

There's nothing here to grasp. T-stop is the same thing as f-stop, except the manufacturer or a third party has physically tested the lens to find how much light it transmits, rather than making a ...
Myridium's user avatar
  • 567
7 votes
Accepted

Why isn't glass transparency part of the exposure calculation?

It IS part of the exposure calculation in fully professional cinematography; these folks prefer lenses marked in T-stops. A full F-stop is actually a factor of two (or one half) in light transmitted, ...
rackandboneman's user avatar
7 votes

How many extra stops do monopods offer for tele photographs?

It's instructive to look where monopods are most often used: sporting events, and shooting wildlife. In all of these cases, it's not a matter of "how many stops" a monopod can provide. It's simply a ...
scottbb's user avatar
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7 votes
Accepted

What's the difference between aperture value and f-number?

The Exif standard says that: $$\text{ApertureValue}=2\log_2(\text{FNumber})$$ which is also: $$\text{ApertureValue}=\frac{2\log(\text{FNumber})}{\log2}$$ There is even a nice conversion table: ...
xenoid's user avatar
  • 21.4k
6 votes

Confused about T-stop number. Does it account for crop factor?

The f-stop is a simple ratio. It is the focal length divided by the working diameter. We use this value to compare the image brightness of one lens vs. another. The f-stop is often in error because it ...
Alan Marcus's user avatar
  • 39.2k
6 votes

Why does illuminance stay the same for a given f-stop even when focal length changes?

Illuminance is "the amount of luminous flux per unit area." Suppose the 100mm lens was aimed at a large wall, and suppose distance was so that the lens sees a 10 x 10 foot area of that wall, ...
WayneF's user avatar
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6 votes
Accepted

How does sensor size affect minimum front element size for a given f-stop and focal length?

How does sensor size affect minimum front element size for a given f-stop and focal length? It affects the width of the angle from which the entrance pupil should be visible when looking through the ...
Michael C's user avatar
  • 175k
5 votes
Accepted

Flash guide number f/stop calculation

However, 25 is NOT 2/3 of the way between 16 and 32. You just have to remember that the scale is exponential, not linear. 4 2/3 stops allows 24.66 more light, and 24.66 = 25.28132..., or roughly 25. ...
Caleb's user avatar
  • 31.7k
5 votes
Accepted

Why do lower f-stop numbers mean larger apertures?

/ is division. A number divided by 22 (f/22) is smaller than the same number divided by 2 (f/2). As simple as that. Now, WHY? f is the focal length. Describing the aperture as a fraction of the ...
szulat's user avatar
  • 5,059
5 votes

Why do lower f-stop numbers mean larger apertures?

The f stop is a comparison between the physical size of the focal length and the aperture. If the aperture is 25mm and the focal length is 100mm, then you'd have f/4 because the aperture value is 1/...
OnBreak.'s user avatar
  • 20.5k
5 votes

Why isn't my F Stop changing on my Nikon D7200?

F0 with a triangle next to it is a Nikon error code for no lens communication. Try cleaning the contacts and remounting the lens. If neither works, try another lens. If that doesn't work the camera ...
Steven Kersting's user avatar
4 votes

Why doesn't the f-stop on my D7100 change when I hold +/- and change the dial in manual mode?

I'm guessing you moved to the Nikon D7100 from a lower tier model Nikon camera that only has one control wheel. With such a camera you must hold down the +/- button while moving the only control wheel ...
Michael C's user avatar
  • 175k
4 votes

What is an easy way to remember the full stop scale?

The f-number set is rooted in the geometry of circles. This is true because the iris diaphragm of a lens normally opens and closes as a circular opening. The f-number set establishes a set of numbers ...
Alan Marcus's user avatar
  • 39.2k
4 votes
Accepted

How does having a large diameter make the SEL85F1.4 a premium lens?

As we calculate FStop as FocalLength/diameter this implies that this lens must be having huge diameter to achieve 1.4 Fstop. Larger than a lot of lenses, but not "huge" in human terms - ...
Philip Kendall's user avatar
3 votes
Accepted

depth of field and f-stop

Depth-Of-Field calculations are daunting. We are talking about the distance before and behind the point focused upon that will have acceptable sharpness. Math models are based on the tolerable size of ...
Alan Marcus's user avatar
  • 39.2k
3 votes

Confused about T-stop number. Does it account for crop factor?

I'm going to highlight and expand on a bit from my answer to Can a smaller sensor's "crop factor" be used to calculate the exact increase in depth of field? The key thing is: In all ...
mattdm's user avatar
  • 143k
3 votes

My Tamron 100-400mm f/4.5-6.3 jumps to f/6.7 beyond 360mm

Fascinating! Your camera is reporting f-numbers not only in 1/2 and 1/3 stop increments, but is also using f/5.3 and f/6, which are both about halfway between two values on the 1/3 stop scale. It is ...
Michael C's user avatar
  • 175k
3 votes

How do constant aperture zooms produce identical exposure, even though focal length is larger?

Shouldn't there be more light coming into the lens? No, because the lens is collecting light from a narrower angle of view. But beyond that, exposure is about brightness per unit area, not about ...
Michael C's user avatar
  • 175k
3 votes
Accepted

How many extra stops do monopods offer for tele photographs?

How many extra stops do monopods offer for tele photographs? In general I've found a monopod buys about three or four stops slower than the 1/(focal length X crop factor) rule for non-stabilized ...
Michael C's user avatar
  • 175k
3 votes

What's the difference between aperture value and f-number?

The AV (Aperture Value) is an expression that tells how many stops away from f/1 an aperture is. Since f/1 is zero distance from f/1, it has an AV of zero (0) Since f/1.4 is one stop slower than f/1,...
Michael C's user avatar
  • 175k
3 votes

How does having a large diameter make the SEL85F1.4 a premium lens?

Can someone please explain how having a large diameter makes it a premium lens. The point is also indirectly linked - manufacturers usually create slower entry level lenses with budget specs, like ...
Dynat's user avatar
  • 141
3 votes

Why smaller AoV APS-C has same aperture as larger AoV FF lens?

The difference in angle of view is due to the smaller image sensor size, not the lens or it's aperture. APS-C lenses can be made cheaper and smaller because their image circle only has to cover the ...
Mike Sowsun's user avatar
  • 12.3k

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