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Questions tagged [f-stop]

The f-stop of an optical system expresses the diameter of the entrance pupil in terms of the focal length of the lens; in simpler terms, the f-stop is the focal length divided by the "effective" aperture diameter. It is a dimensionless number that is a quantitative measure of lens speed, an important concept in photography.

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4 votes
2 answers
2k views

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

In macOS Finder it says a photo taken at f/2.8 has an aperture value of 3. What is an aperture value, and how is it different from f-stop?
11 votes
4 answers
3k views

Why are 1/3 stop apertures uneven numbers apart?

Why do 1/3 stop apertures go like 8, 9, 10, 11, 13, 14, 16, 18? There's a difference of 2 between 11 and 13, it goes back to 1 between 13 and 14, and it goes back up to 2.
1 vote
2 answers
222 views

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

I can use the dial but the number never goes up or down. It stays at 0. I tried holding down the +/- while turning the front dial and it just adjusts the amount of light coming into the view finder. ...
68 votes
4 answers
153k views

What does f-stop mean?

What does f-stop mean? Is it the same thing when people say "2 stops" for example?
3 votes
5 answers
3k views

Do you get more bokeh on a APSC sensor with a full frame 50mm f/1.8 lens or a APSC 30mm f/1.4?

I am trying to compose a detail shot where I want to get as much background blur as possible. I am using Sony a6500 camera (APSC 1.5x crop factor body). I am considering two lenses: Sigma 30mm f/1.4 (...
1 vote
1 answer
754 views

How to keep the aperture of an adapted Nikon G lens open?

I would like to leave my lens fully open all the time without having to find an aperture converter. But other than bluetac I cannot find anything that would attach to my Nikon lens and leave it ...
2 votes
6 answers
227 views

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

I am quite confused, FF focal length 50mm f/2.0 has aperture diameter 25mm APS-C lens 50mm f/2.0 has aperture diameter 25mm Then both lenses have same size front glass. However Angle of View for lens ...
14 votes
5 answers
37k views

What does the f-stop printed on the lens refer to?

I have read this,so I know what an f-stop is, but what does the number on printed the lens signify? Is this is the maximum f-stop, the ideal, or something else?
2 votes
6 answers
1k views

How do I calculate f/stop change for teleconverter that increases lens magnification?

I'm trying to calculate the f/stop change of attaching a x2 teleconverter to a 80mm f/2.8 lens. In this instance, the teleconverter attaches to the front of the lens, and has a larger opening than the ...
2 votes
3 answers
337 views

For the same FOV and f-stop, will total luminous flux increase linearly with sensor area?

Suppose I have two different cameras, one with a sensor whose area is twice the other's. Further assume the sensors have the same aspect ratio. Suppose I put 35 mm-equivalent lenses on both, thus ...
-3 votes
3 answers
213 views

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

I have been reading about Focal length and Fast lenses when I came across this lens which has 85mm focal length and F1.4 as FStop. https://www.sony.co.in/electronics/camera-lenses/sel85f14gm Generally ...
1 vote
2 answers
190 views

How can I compute low light performance for different formats?

How can I compare low light performance for different formats? Are there some standard equations to do this? For example, let's say I want to compare these three camera-lens combinations: Nikon ...
20 votes
3 answers
3k views

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

I understand the difference between f-stop and t-stop, but why are cinema lenses measured in one, and dSLR lenses measured in another?
0 votes
1 answer
336 views

How do you calculate ND filter value of gray sunglasses and the colored sunglasses?

I had the idea of using my sunglasses as ND filter when F/16 didn't help in a beach scene with my MC 2500 but then realized something weird. My green Ray Ban cockpit sunglasses claim to block 85% of ...
0 votes
4 answers
315 views

Dynamic range of an HDR photo

I was wondering what is the dynamic range of an HDR photo if the bracketing was set at 2EV? (in F-stops)
7 votes
3 answers
4k views

What's the formula for f-stop equivalence between different sensor sizes?

The famous Group f/64, to which Ansel Adams and several other prominent photographers of that day belonged, were named that because of the f-stop: The term f/64 refers to a small aperture setting ...
31 votes
10 answers
85k views

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

If you were teaching someone new to photography the full stop scales, is there a better way then flat out memorizing these values? Does anyone have an easy way that they remember the scale? Would it ...
5 votes
6 answers
2k views

How many extra stops do monopods offer for tele photographs?

I have often wondered what the purpose of monopods is. It seems to me that they remove only two degrees of freedom out of three possible degrees of freedom of camera shake. And the situation is even ...
0 votes
3 answers
148 views

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

The F number is a ratio calculated purely from the focal length of the lens and the size of the aperture. Any light meter talks in terms of F, Shutter, and ISO. Different glass, or just different ...
9 votes
4 answers
1k views

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

I've noticed that many older lens have just hard f-stops for lens (2, 2.8, etc). However, since the aperture wheel for some is continuous you can "stop" are some arbitrary point and shoot. From my ...
23 votes
7 answers
13k views

How can aperture be f/11 on a lens with an aperture range designation of 3.5-5.6?

I made a series of outdoor shots with Nikon D5000, with the 18-55mm 1:3.5-5.6G VR kit lens. On some shots, I see in the EXIF info f/11, and in another shot, f/9. How can that be, that the f-number ...
0 votes
2 answers
118 views

Aperature/f stops/lenses [duplicate]

I am interested in landscape photography and a common point I hear thrown around is that a higher aperture (f11-f22) is best for landscape photos. However, every blog, YouTube video and photography ...
0 votes
2 answers
65 views

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

My understanding is that a larger focal length corresponds to a larger working aperture diameter, since the numerator is larger. Why doesn't a larger working diameter correspond to a brighter image? ...
8 votes
3 answers
4k views

Does autofocus work better with f/2.8 lenses vs f/4 or slower?

I read following in a web site (http://realphototips.wordpress.com/tag/ai-servo/) Lenses with maximum apertures of f2.8 allow the camera to use all high precision sensors. In low light or other ...
0 votes
1 answer
258 views

How is the diameter of a non-circular (effective) aperture actually measured?

An f-number is determined as the ratio of the focal length to the diameter of the entrance pupil. But the actual aperture diaphragm is usually not a perfect circle. Its shape is determined by the ...
2 votes
5 answers
3k views

Why do lower f-stop numbers mean larger apertures? [duplicate]

I thought this would have been asked before but it seems not. I don't understand how f-stops are numbered. From what I read, the lower the f-stop number, the larger the aperture. That is, f/2 is ...
15 votes
4 answers
10k views

Does using an extender actually change the aperture of the lens?

I just bought a Canon 2X extender and I always believed that it would only result in 2 stops' loss of light and not change the aperture. However, when I tested this extender on a Canon 135mm f/2 ...
6 votes
3 answers
282 views

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

Does the sensor size affect the needed size of the front element given a focal length and f-stop? My intuition tells me that a bigger image circle would require a bigger front element to maintain the ...
0 votes
5 answers
14k views

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

On my Nikon D7100, the f/stop will not go down from 14 when I hold down the +/- button and turn dial. All I get is a little number below but the photos do not change exposure when I change this number....
2 votes
2 answers
790 views

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

I got a brand new lens today: a Tamron 100-400mm F/4.5-6.3 Di VC USD. I have mounted it on my Nikon D80. This lens seems to have a problem with its aperture: At 100mm, I can operate from f/4.5 ...
9 votes
2 answers
663 views

Is there something special about f/3.5-5.6?

The vast majority of the kit lenses sold with entry-level (or even upper entry-level) interchangeable lens cameras, tend to have an aperture range of f/3.5-5.6. This seems to be independent of whether ...
21 votes
5 answers
11k views

Where does the term "f-stop" come from?

Does anyone know the origins of the term?
1 vote
2 answers
295 views

depth of field and f-stop

I have a thorlabs DCC1545M camera. https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=4024&pn=DCC1545M e.g. it has a 1/2 inch format, a sensor size of 6.66mm*5.32mm, with 1280*1024 ...
3 votes
3 answers
2k views

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

I understand that a T/stop number deals with how much light is let in, instead of the sensor size vs. aperture like the f/stop number. However, what I haven't found is whether or not that T/stop ...
1 vote
1 answer
844 views

Will the F-stop Loka or Ajna fit a Macbook Pro 15"?

I'm currently looking at getting a new camera bag that I can use to fit a bit of gear (listed below) and wanted to know if anyone has/had one of these bags and in particular if it will fit a 15" ...
0 votes
2 answers
13k views

How is f-stop a measure of dynamic range?

As far as I have read f-stop is a measure of the aperture. This affects the amount of area in the foreground and background which is in focus. While having a look at the dynamic ranges of cameras I ...
8 votes
5 answers
1k views

Do top-of-the-line lenses transmit more light at the same f-stop?

We usually refer to the F number to compare how fast is a lenses with another one. I understand that the optic quality should help as well — so would a L series in Canon (or whatever is the equivalent ...
0 votes
1 answer
325 views

What are some general rules for astrophotography?

What are the generally accepted guidelines for iso, f-stop, aperture, etc. that help take better pictures of the stars? In the past I've mostly used a small webcam that fits over the eyepiece of my ...
4 votes
5 answers
597 views

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

I'm aware this is flirting with video rather than photography, but the question really relates to how each world can be understood by the other. Very briefly - I am an amateur photographer who ...
7 votes
2 answers
2k views

Bracketing with ISO or exposure time?

With old cameras, you had film with fixed ISO and you could bracket your shots by either adjusting the f-stop or exposure time. Normally, if I have enough light, I prefer to keep the f-stop constant ...
1 vote
1 answer
459 views

How to photograph oil and pastel art works with DSLR? [duplicate]

I'm using a Nikon D800 with a prime Sigma 50mm f1.4 lens to photograph a selection of artwork for producing an art book. I will shoot in raw format. My questions are: What light source will look ...
36 votes
4 answers
8k views

How do you find out the "sweet spot" of a lens?

I've tried googling this, but have never found a satisfactory answer. I've heard the term "sweet spot" thrown around by some photographers to mean the f-stop of a lens which results in the highest ...
0 votes
1 answer
253 views

How does focus breathing affect DOF?

Like explained in this question Does focus breathing make a lens slower when close focusing? focus breathing does change the effective F-stop. At the same time, the lens behaves, as if it was a ...
3 votes
4 answers
1k views

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

I'm trying to wrap my head around the math/physics of how illuminance on the film/sensor plane remains equal for a given f-number regardless of the focal length of the lens. Since a longer lens will ...
1 vote
1 answer
124 views

How to shoot the sequence of adjusted exposures wanted for a ColorChecker?

I'm trying to shoot a sequence of photos needed for calibration. As instructed, I'm in manual mode, with fixed ISO 100 (camera dafault), and other values read from the lightmeter ... and now: Can you ...
24 votes
7 answers
11k views

Why don't compact digital cameras have the aperture range of DSLRs?

Why is it that on compact digital cameras the aperture never seems to go any smaller than about F8 ? Even on high-end compacts such as the Canon G10 or Panasonic LX5. Is there some practical or ...
2 votes
2 answers
1k views

Does crop factor affect exposure time?

I'm confused on this, even after researching: Given 2 cameras- one full frame with 50mm lens, one Micro Four Thirds (2x crop factor) with 25mm lens, let's pretend the cameras are beside each other, ...
13 votes
2 answers
622 views

Does focus breathing make a lens slower when close focusing?

I've heard that focal length of some lenses will become noticeably longer when focusing to a close distance, an effect called "focus breathing". Since f-number is focal length divided by diameter of ...
0 votes
1 answer
666 views

How to choose f-stop / depth of field? [duplicate]

I am fairly new to photography and I have read many "beginners guides" and watched youtube tutorials. One thing that remains elusive to me is how to properly pick what f-stop to use. I use a 35mm, ...
2 votes
2 answers
2k views

Flash guide number f/stop calculation

I have been reading the B&H Speedlight Buyer's Guide. I am confused specifically about the guide number calculation. I understand the principle and how the inverse square law is used. Here is the ...