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It happens a lot. People refer to the aperture being small (or big!). By default does this imply a small opening of the iris (literal aperture), or a small f-value (how the aperture is measured, for which the value gets bigger as the iris gets smaller)?

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I try to never use simply the adjective big or small to describe aperture, I also include an example of a big or small aperture(f/x). This especially helps those not familiar with photography terms. We can agree to the "best" method here, but to a beginner the definitions given in line help the most. –  dpollitt Apr 27 '13 at 21:01
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The value does not get bigger as the iris gets smaller any more than the value of a fraction gets larger as the denominator increases. –  Michael Clark Apr 28 '13 at 11:20
    
But still, the actual number is getting larger. It's counter intuitive to say that f/1.8 is larger than f/22, and that's why I thought this question might be valuable. –  Good Gravy May 2 '13 at 14:42
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4 Answers

up vote 8 down vote accepted

Unless there's further context about physical size, "small aperture" almost always means a higher f-number. This is also, of course, a smaller physical size for a given lens relative to wider apertures.

A small aperture means a high f number, like f/22 or f/32. Where one draws the line is open to interpretation, and to context. A small aperture is also called slow (because it lets in less light, requiring a longer shutter speed to compensate).

This means that a "smaller f-number" where the number is low is a larger aperture, not a smaller one. That's a bit confusing, so really it's better to avoid "small" and "large" (or "high" and "low") altogether and talk about "fast" and "slow".

Here's a quick aperture "cheat sheet":

f-stop chart

(Note that the maximum "wide open" aperture will vary based on each lens design. f/2.8 is common for high-end zooms and f/3.5 to f/5.6 for cheap ones. Many prime lenses are faster. At the other end, most lenses for APS-C or 35mm stop down to f/22 or f/32.)

Charts like the one above used to come with cameras, usually along with suggestions for lighting conditions appropriate for each. But these days with instantly-variable digital ISO (rather than swapping film), and with point and shoot cameras just doing everything automatically, it's left for intermediate photographers and above. If you want to progress beyond point and shoot, though, familiarity with this scale remains important.

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@bRadGibson Yes, good point. I've edited to hopefully be less ambiguous (and pointed out how confusing the ambiguity can be!). –  mattdm Apr 27 '13 at 21:26
    
Looks good to me! And for those wondering about where the terms "fast" and "slow" come from, they refer to the shutter speeds you'll need to use to expose properly when shooting at large and small apertures, respectively. –  bRad Gibson Apr 27 '13 at 22:05
    
Nice chart, Matt. May I suggest removing "small number but" and "larger number but" in the second lines under the graph? Those terms perpetuate the confusion beginners experience, plus are captured by the "low f-numbers" and "high f-numbers" immediately above. –  bRad Gibson Apr 27 '13 at 22:50
    
Requires a longer exposure time OR higher ISO. Other than that minor knit picking correction, very nice answer (mainly because you mention fast and slow apertures, which is how I describe it in conversation!) Do you also describe ISO as fast and slow? Could it be worth opening another question I wonder... –  Good Gravy Apr 28 '13 at 0:40
    
I thought it important to have the "but" line in there, because it's really the essence of the question. –  mattdm Apr 28 '13 at 13:16
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This is confusing for many beginners. If you're talking to a beginner, all bets are off! :)

If you're talking to someone with knowledge in the space, the term "small" or "large" aperture do indeed refer to the physical size of the opening, and not the numeric value.

You may see a "small aperture" also referred to as "stopped down" or a "high f-number".

A "large aperture" may also be referred to as "opened up", "wide open" or a "low f-number".

Good question. I hope that helps.

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I tend to use wide and narrow to avoid such ambiguity, and usually include an actual f-number such as f/2.8 or f/16. I'm also always careful to include the "/" to remind anyone reading that the f-number is a fractional ratio, so that 1/4 is larger than 1/16.

When reading what others have written I tend to use context to try and determine what they meant by a high or low aperture. If it can't be determined I will usually ask via a comment or reply, depending on the format of the discussion.

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Not using the "/" is probably big part of many misunderstandings. I see often in online camera sales how aperture of a lens is written simply F2.8 or F4. That looks like the letter F was meaning "Aperture". Even beginners would more easily understand the meaning if written with the divider; that "f" is being divided by the number that follows. –  Esa Paulasto Jan 7 at 16:01
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Agree completely with saying "wide" and "narrow" instead. Just as accurate a description and less confusing. –  mpr Jan 7 at 18:37
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Aperture refers to the opening in the lens. Small aperture should then mean that the lens has a smaller opening. The aperture size is denoted by numbers which are rather confusing. We use small number for big apertures and vice versa.

Aperture is denoted by 'f' numbers like f/4, f/2.8 etc. Do these numbers really make any sense? They do for sure and this is how. In 'f/4', 'f' means the focal length of the lens being used. '/' means divided by and '4' is numerical '4'.

Suppose we are using a 100mm lens on our camera and shooting at 'f/4', the aperture size is 100/4, which is 25mm. At f/8, the aperture size will be 100/8 or 12.5mm. Hence, the bigger the 'f' number the smaller is the aperture.

These calculations can be verified if the lens is a simple lens. Since our camera lenses are complex in construction and they have many elements, the physical aperture size coule be lesser than what your calculation says. Eg:- A 600mm f/4 lens doesn't have a aperture diameter of 150mm. Lens designers strive to keep the size manageable with complex construction and make our life simple by providing a luggable lens.

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