# Tag Info

20

This is really simple when you think about it. The additional element changes the focal length of the lens, without changing the apparent size of the aperture. That means that the relative size of the aperture decreases, so the f number does in fact actually change. (If this is unclear to you, see the bit about f numbers in this other answer.) This is also ...

20

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). You might say But t-stops are more accurate, allowing me to be more precise! — and that's basically right, but the main thing is that precision is overrated in ...

20

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 the Precise Numbers is of course the theoretical precise goal numbers that the camera designer certainly aims for. There can be no question about those (even if ...

19

Let's start with lenses at the same location, and then address the moving the longer lens farther away to get the same field of view. Lenses at the same location The 50mm f/1.4 lens has an effective aperture that's twice the diameter, and four times the area, of the 25mm f/1.4 lens. The 50mm will, therefore, collect four times as much light (four times as ...

17

Dynamic range is not measured in f-stops, it is measured in stops. A stop is often used to refer to a change that doubles the value or, in the case of cameras, the amount of light. Changing the aperture by one f-stop doubles to amount of light allowed in, so in the case of aperture, a stop is an f-stop. Similarly, cutting the shutter speed in half is a ...

17

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. F-stop is the literal proportion of the aperture to focal length. T-stop adjusts this for exposure, but this raw value is important to depth of field. Depth of ...

16

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 adjust exposure as needed. Cinematographers need to control exposure first and then compose as needed. The critical difference with photography is that we can ...

14

The f-stop is more directly relevant to photographers because it normalizes out the focal length. It then gives you a measure of how bright the image will be on the sensor relative to the scene brightness. For example, if a scene is well exposed with a 50 mm lens at f/8 and 1/200 second, then it will be well exposed with any other lens at f/8 and 1/200 ...

13

An f-stop is a mechanism for setting the aperture of the lens, or how wide it is opening to let in the light. There's two parts to it: f and stop. First, the maths. f-number An f-number is a number in the form f/2.0 which specifies the size of the aperture opening. f refers to the focal length. f/2.0 means the diameter of the aperture opening is the ...

13

It's not linear because it's based on area rather than lines. Or, to put it another way, the scale isn't based on square roots. It's based on the actual math that represents the physical properties of the system, and it happens that exposure doubles when aperture size opens by a factor of the square root of 2. If you remember back to your elementary-school ...

13

"Therefore lens 2 has a larger maximum aperture than lens 1 and therefore capability to allow more light. This is where your understanding is not quite right. The physical size of the aperture is indeed larger in the longer lens, but it does not allow in more light, because the longer focal length means that the field of view is narrower. This means that ...

13

If you look at filter #209 you'll see "Reduces light 1 stop (Transmission = 51%)". That is what you expect to see. Filter #210 reduces light 2 stops and has transmission of 24%. Again, what you expect. So what is the matter with filters 207 and 208? They are COLOR filters not neutral. They a) reduce light, and b) reduce it differently in different ...

13

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 same number, but they would still be measures of different things. T-stop measures how much light is passed through the lens, f-stop measures the size of the ...

12

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 circular hole, into a slit in the lens barrel. The photographer had a series of these metal slides called Waterhouse Stops after John Waterhouse circa 1858. The ...

11

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 the right of the decimal. Such a number is defined as an irrational number. In photography we round the actual values of many irrational numbers to a simpler ...

10

The intention is that the actual exposure should be exactly the same for equivalent exposure settings, but there are small deviations. There are also some other differences to the images other than the obvious (e.g. different depth of focus for different apertures). Here are some differences that you may experience when choosing a different setting with the ...

10

In a theoretical sense, these things are perfectly interchangeable. See the second half of my answer to What is the "exposure triangle"? (after I get done ranting about the terminology). This is actually exactly the point of the "stops" system — you can think in terms of Exposure Value (measured in stops) and not need to worry about any complicated ...

10

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 (potentially heavy) lens, so its shaking is no longer caused by your muscular control, itself affected by muscular fatigue(*). Of course the 55-250mm is a rather light ...

9

Yes, there have been numerous lenses made that are faster then f/1.0 One of the most famous is the Zeiss_Planar_50mm_f/0.7 which was was designed for the NASA and used by Stanley Kubrick in Barry Lyndon to shoot several indoor scenes by candlelight. Zeiss_Planar_50mm_f/0.7

8

It is mainly about the cost/benefit ratio of making cheap lenses. It doesn't cost a lot more to make a lens f/3.5 than f/8 at an 18mm focal length since the entrance pupil (sometimes referred to as the effective or apparent aperture) is still well within the diameter of the mounting flange used by most interchangeable lens camera systems. As the lens is ...

8

There are two factors determined by physics that favor autofocusing with wider apertures. More light An f/2.8 lens lets in twice as much light as an f/4 lens. The more light an AF system has to work with the faster and more accurate it can be. Signal-to-noise ratio affects performance of the sensels on PDAF sensors the same way that it affects performance ...

8

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 theoretical calculation based on the size of the exit pupil, which is where the f-stop measurements come from. When a manufacturer specifies T-stops on their lens,...

7

When the camera is focussing the lens, the lens is wide open, the aperture is only closed down to the selected setting when you actually close the shutter. So, based on that, an F/2.8 lens will let in twice as much light for autofocusing as the F/4 when wide open. Did you make a mistake? Possibly not. The Nikon F/4 variants of the F/2.8 lenses are very good ...

7

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, while the typical transmission losses of a lens are in the range of an eight to a quarter stop. This makes transmission nearly irrelevant to correct exposure, ...

7

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 matter of increasing the keeper rate of shots. Competitive Sports (football, soccer, etc.) Monopod are ubiquitous along the sidelines of professional football (...

7

The Exif standard says that: ApertureValue=2*log₂(FNumber) which is also: ApertureValue=2*log(FNumber)/log(2) There is even a nice conversion table: However, looking at my own photos (EOS 70D), I find that the exposure value and the FNumber are close to each other but not always equal, so this doesn't follow the table below for apertures => f/8. So I ...

6

Your 25mm f/1.4 and 50mm f/1.4 lenses will gather exactly the same amount of light - one of the primary reasons that f-stop is a useful concept is because it directly represents light-gathering capability.

6

The f number is the inverse square root of the light collection efficiency. Why such a crazy relationship? First - let me define "light collection efficiency". You build an image by collecting photons (light particles) with your lens, and focusing them onto the film / sensor. If you double the area of your lens, you collect twice as many photons - so you ...

6

No. You can imagine the micro4/3 to simply cut out the middle of the image. If you had a 25mm lens on a full frame camera and exposed it properly, the middle part of the frame is part of what's exposed properly. The definition of f-stop factors out the lens length so only f-stop and shutter speed determine the EV (exposure value). Let me make this clear: ...

6

The value (f/1.6) at the top is the aperture used when the picture was taken. The aperture value under Camera Data (Exif) (f/1.4) is the maximum aperture value to which the lens can be set.

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