I am hearing lot of people/website talking about aperture very often. But different website writes it different way.

What is the correct way to mention it? E.g. If some good camera phone has aperture 1.8. So it would be written as f/1.8 or f1.8? Is it lesser the aperture better the camera or more the aperture better the camera? E.g which one is better f1.8 or f2.2?

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    You're asking two questions here: 1) What's the right notation for aperture? and 2) Which aperture value is better? Those are very different things, and we encourage people to stick to one question per post. You'll find lots and lots of existing questions here about how aperture affects image quality, so I suggest you remove the second question and look at existing answers instead. – Caleb Oct 26 '17 at 20:20
  • Only best, brave thing about your comment is that you donwvoted and you cared to put comment about it. Secondly its one question, not two questions you need to read it again. Last, see we made the rules, rules didnt made us. When you see people are answering and its genuine question with no BS then why you are carrying and running torch of BS alone on the road. – paul Oct 27 '17 at 5:27
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    I didn't downvote, but I will if you want... And So it would be written as f/1.8 or f1.8? is certainly a distinct question from Is it lesser the aperture better the camera or more the aperture better the camera? If you don't see that, you need to read it again. – Caleb Oct 27 '17 at 5:32
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    And if you didn't mean to ask two separate questions, can you please clarify which you are interested in? It looks like two questions to me too. This isn't a forum (I see you've been on Stack Overflow for a while, so you know this!). Things just work better when each question is one single answerable topic. – Please Read My Profile Oct 27 '17 at 8:22
  • Yeap, 2 questions here: one about the importance of "/" in f(/)2.8 and the other probably about what is "best" for a lens regarding aperture. I translate the second question as "When I compare f/2.8 to f/1.8, should I say that f/1.8 is a lesser aperture or a better aperture ?". Either way, aperture is really about the lens, which is a subpart of the camera. – Olivier Oct 31 '17 at 17:36

So it would be written as f/1.8 or f1.8?

Doesn't really matter.

E.g which one is better f1.8 or f2.2?

1.8 lets in more light compared to 2.2, but that doesn't necessarily mean it's better.

Also, aperture is not a factor of a camera, it's a characteristics of the lens. The lower number actually means a bigger aperture and vice versa.

You'd adjust the aperture when you want to control how much light you want to let in and when you need to control the depth of field.

low number = large aperture:
- lets in more light
- shallow depth of field

big number = small aperture:
- lets in less light
- deeper depth of field

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  • Too small an aperature, and diffraction could soften the image. Too big an aperature, and typically lenses aren't all that sharp either. This could be a flaw, or a desired effect. – Calyth Oct 26 '17 at 19:08
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    @paul The larger the lens diameter, the more correction is needed to counteract aberrations such as chromatic aberration. Most lenses aren't their sharpest until stopped down a stop or two. Sometimes a similar lens with a narrower max aperture will be sharper at common apertures than a more expensive, wider aperture lens of the same focal length range. The $1,300 EF 16-35mm f/2.8 L II vs. the $1,000 EF 16-35mm f/4 L for instance. The f/4 lens is sharper across most of the aperture and focal length range. – Michael C Oct 26 '17 at 19:26
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    @paul An aperture of f/2.2 can not be "reduced" to f/1.8 because f/1.8 is larger/wider than f/2.2 in the same way that 1/1.8 (0.555555) is a larger number than 1/2.2 (0.454545). If a lens' maximum aperture is f/2.2 it is incapable of being set to f/1.8. – Michael C Oct 26 '17 at 20:34
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    It may help to think of aperture number as the level to which the aperture blades are closed,rather than opened. While it is not exactly true, it serves for making sense of the numbers. So a lens with a "level of closedness" 1.8 is less closed than one with level of closedness 2.2. So it lets through more light. – Gnudiff Oct 26 '17 at 21:16
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    I disagree. It does matter how the aperture is specified. – Stan Oct 27 '17 at 0:54

All else being equal, a larger aperture (smaller f number) is better because it lets in more light, but the problem with "all else being equal" is that it is never true, especially with fixed-lens cameras such as cellphones where you can't put different lenses on the same body (or the same lens on different bodies).

There can be many reasons why a lens lets in more light but the resulting image quality is lower than with another lens that lets in less light. A lens might let in more light but otherwise be of inferior optical quality (less careful design or manufacturing process, cheaper materials), resulting in a loss in sharpness and in various optical artifacts (chroma aberration, etc.). The sensor and imaging processor to which the wider lens is coupled may be of inferior quality (smaller or older-generation sensor, slower processor, inferior image processing algorithms). And finally the wider lens may be so much more expensive (in money, but also possibly in size/weight) that it is simply unaffordable to you, which means that the image quality of the pictures you can take with it is effectively zero.

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  • " All else being equal, a larger aperture (smaller f number) is better because it lets in more light, " Not if more light Results in over exposure. The best aperture is the one that is correct for the shutter speed you're using in order to achieve correct exposure. – Alaska Man Oct 27 '17 at 4:41
  • Ever heard of ND filters? Light is like money; if you have too much of it you can always throw some away, but if you don't have enough, you're out of luck. – user29608 Oct 27 '17 at 5:10
  • @Alaskaman if DOF and overal look of the image are important, the "best" aperture might depend on more details than just exposure time. – Gerhardh Oct 27 '17 at 6:40

Lens apertures are expressed as a mathematical ratio.

F#, f-number, 1:#, and f/n (ex. f/2.2) are unambiguous ways to express the quantity as a ratio to the focal length.

It does matter how lens apertures are expressed.

Not enough information is provided for a qualitative assessment of any specific setting compared with another.

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The lens manufacturers write it as f/1.8. This is because the meaning is that f/number is focal length / effective diameter, i.e., it is a division, of f/diameter.
A 50 mm f/1.8 lens has an aperture diameter of 50/1.8 = 27.78 mm diameter.

f/2.2 is likely a better quality lens (less aberrations, a wide aperture becomes difficult), and is smaller, lighter, and less expensive, but f/1.8 opens wider to see more light in a dim situation.

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    Zeiss, for example, express it without any f like this: ZEISS Loxia 2.8/21 – osullic Oct 26 '17 at 19:05
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    "f/2.2 is likely a better quality lens" You cannot say this based only on apertures. And saying this gives "newbies" the wrong idea. – osullic Oct 26 '17 at 19:06
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    In the olden days, it might be written on the lens as 1:1.8 or 1:2.2. – user50888 Oct 26 '17 at 20:06
  • Sony writes "F2.8", not "f/2.8". – Please Read My Profile Oct 26 '17 at 22:15
  • So possibly I should have said "Virtually all lens manufacturers say f/1.8" ? Almost all other uses do too, Wikipedia, reviews, etc. B&H and Amazon describe Sony and Zeiss lenses with f/ . Even Zeiss lenses for Sony are described f/. :) – WayneF Oct 27 '17 at 1:42

What we are actually after is a way to compare the image brightness that a camera system will cause to play on film or image sensor. Now the lens acts like a funnel in that the larger its working diameter, the brighter the image will be. Additionally, the focal length is the projection distance from lens to film or image sensor. The longer the focal length the more the image will be magnified. The more the magnification, the dimmer will be the projected image. We need a universal way to compare one camera lens with another to get a handle on image brightness. This comparison needs to be universal. In other words, a method that works regardless of the working diameter and the focal length.

If we can find such a universal method, we can compare a tiny camera to a giant astronomical camera had make common comparisons as to image brightness.

We have such a method! Ratio to the rescue: A ratio is dimensionless. We divide the focal length by the working diameter and get a value we call the focal ratio. Such as, what is the focal ratio of a lens 400 feet in focal length with a working diameter of 40 feet? Answered 400 ÷ 40 = 10 written as f/10. We can compare this lash-up to a system that is 40 inches in focal length with a working diameter of 4 inches. Thus 40 ÷ 4 = 10 written as f/10. We can compare both to a miniature camera 40mm focal length 4mm working diameter thus 40 ÷ 10 = 10 written f/10

What I am trying to say: The focal ratio is universal, it is void of dimension. Any lens system operating at the same focal ratio delivers the same image brightness when imaging the same object illuminated the same way. Now we abbreviate focal ratio at f/# or as f-number or aperture f-#. All this means the same, we just write the ratio a different way.

The f-number set is by tradition a change (delta) of 2X. Meaning a doubling of halving of the amount of light allowed to play on film or digital sensor. Since the lens is a circular figure, we fall back on the geometry of circles. If you multiply the diameter of any circle by the sq. root of 2 = 1.4, you calculate a revised circle with twice the surface area. If you divide the diameter by 1.4, you have calculated a revised circle with half the surface area.

Using the 1.4 factor, the f-number set is:

1 – 1.4 – 2 – 2.8 -4 -5.6 – 8 – 11 – 16 -22 – 32

This is a set with 2X change. We can calculate sets with finer increments of change.

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For me there is no "correct" way to write the aperture number. Because it depends on the location, country.

For example in Germany you can see it as 1:2,8 or 2,8 like Canon EF 4,0/16-35. And the digital delimiter is comma, not dot

In France you can see it as F/2,8 (mostly) or f/2,8 (again with comma)

In UK you will see it as f/2.8


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