Why do most lenses have a smallest aperture of F22?

[thebeardedgroundsman]

I know that the smaller the aperture, the greater the depth of field. However, it seems that most lenses have a sweet spot at around f11 and if you focus 1/3rd into the scene, this seems to give great images.

My Voightlander 50mm is interesting as it's aperture range is f2 to f16 with less significantly drop off after f11 than my Sony 28-105 G zoom at 50mm (not a fear comparison between a prime and a zoom)

Edited October 31, 2022 by thebeardedgroundsman

[XKAES]

I have lenses that only drop to f11, and others that go to f128.  Many manufacturers stop the scale at the point where diffraction is so bad, they don't want customers using that aperture setting.  On most lenses, the best resolution is in the f8 to f16 range -- but if you want more or less DOF for the subject, other f-stops will work fine.

[Prieni]

On 10/31/2022 at 10:03 AM, thebeardedgroundsman said:

I know that the smaller the aperture, the greater the depth of field. However, it seems that most lenses have a sweet spot at around f11 and if you focus 1/3rd into the scene, this seems to give great images.

My Voightlander 50mm is interesting as it's aperture range is f2 to f16 with less significantly drop off after f11 than my Sony 28-105 G zoom at 50mm (not a fear comparison between a prime and a zoom)

You get a greater depth of field, that's true, but you also run into the diffraction limit, i.e. the sharpness decreases the further you close the aperture. This depends on the sensor resolution and aperture size. A good in depth explanation you can find here: https://www.cambridgeincolour.com/tutorials/diffraction-photography.htm
It's also quite instructive to do a test series with some fine structured target (like e.g. a cushion from fine woven fabric) at different apertures. You start with the aperture opened to the max (e.g. ƒ/2.8) and close it further after each exposure. You will see that first the sharpness increases but there is a certain point when it decreases due to the diffraction limit. 
This is why you have sweet spots of sharpness with every lens, just not the same one for all lenses.

[FunWithCameras]

The aperture on most of our lenses uses an iris that moves metal blades slide in and out to make the desired aperture size. The catch is that as you move them closer and closer together tiny errors add up, and you can get inaccuracies. I think most lens makers stop at f/16 (for lens with big maximum apertures like f/1.4) or f/22 (for smaller maximum apertures like f/4 or f/5.6). I imagine the blades get tight as the aperture gets small.

There are exceptions - I think some large format lenses do f/64 or smaller.

When you think about it, f/16 is 7 stops from f/1.4, so it has to let in 1/128 of the light, and you still want the opening to be roundish.

Edited March 31, 2023 by FunWithCameras

[RoryBrady]

The reason behind this choice is primarily related to the physics of light and the characteristics of lens optics.
Aperture controls the depth of field, which refers to the range of distance in a scene that appears acceptably sharp. By selecting a smaller aperture (larger f-number), such as f/22, the depth of field increases, resulting in more of the scene being in focus. This can be useful in landscape or macro photography where you want to maximize the sharpness from foreground to background.

[FunWithCameras]

18 hours ago, RoryBrady said:

The reason behind this choice is primarily related to the physics of light and the characteristics of lens optics.
Aperture controls the depth of field, which refers to the range of distance in a scene that appears acceptably sharp. By selecting a smaller aperture (larger f-number), such as f/22, the depth of field increases, resulting in more of the scene being in focus. This can be useful in landscape or macro photography where you want to maximize the sharpness from foreground to background.

I thought the question was more about why the smallest aperture stops at f/16 or f/22, instead of continuing. You've described why people might choose a smaller aperture, but not why it stops.

I think diffraction limiting, and the difficulty of making an iris that produces a round opening at so small a size, are probably the main reasons.

[RoryBrady]

On 6/17/2023 at 3:06 AM, RoryBrady said:

The reason behind this choice is primarily related to the physics of light and the characteristics of lens optics.
Aperture controls the depth of field, which refers to the range of distance in a scene that appears acceptably sharp. By selecting a smaller aperture (larger f-number), such as f/22, the depth of field increases, resulting in more of the scene being in focus. This can be useful in landscape or macro photography where you want to maximize the sharpness from foreground to background.

I hope most of the things have been cleared in your mind. furthermore, How does the smallest aperture affect the depth of field in photography?

[Pieter]

On 6/18/2023 at 6:41 AM, FunWithCameras said:

the difficulty of making an iris that produces a round opening at so small a size, are probably the main reasons.

I don't think it's the roundness of the opening that matters: many people actually prefer polygonal shapes at small apertures, to get more pronounced sunstars. Bokeh balls are virtually non-existent at small apertures, so the shape of the iris is irrelevant there.

I found an interesting graph here, showing the maximum megapixels on a fullframe sensor that a lens can resolve at a given aperture, due to diffraction:

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What you see is that beyond f/11, any modern camera with 24-30 megapixels will show image degradation when stopping down, unless you value greater depth of field over absolute sharpness. Apertures beyond f/22 will result in a blurry mess on any camera, so it doesn't make sense to allow for smaller apertures. If you really want great depth of field, better do some focus stacking at larger apertures.

 

[FunWithCameras]

I should have phrased it better - I meant that aperture isn't symmetrical if they try to make the aperture too small.

But yes, diffraction limiting does cut in before you get to f/22.

[XKAES]

There are other variables as well.  Diffraction increases with the thickness of the aperture.  That's why pinhole cameras use extremely thin metal plates -- that have fixed, perfectly round, apertures -- to minimize diffraction.  Unfortunately, variable apertures require thicker metal in order to operate.

Also, the format size has to be taken into account.  Larger formats, such as 4x5", have less of a problem with diffraction at f22 or greater because they don't need to be magnified as much to produce the same sized print.  Many large format lenses have f-stops to f128.  Smaller formats, on the other hand, have a bigger problem with diffraction --at f16.

Edited June 20, 2023 by XKAES

[Pieter]

3 hours ago, XKAES said:

the format size has to be taken into account.

That's why I said:

6 hours ago, Pieter said:

the maximum megapixels on a fullframe sensor

[AmirDeclan]

The aperture setting controls the depth of field, which is the range of sharpness from near to far in an image. Smaller apertures, such as F22, allow for greater depth of field, meaning more of the scene will be in focus. This is particularly useful for landscape photography or when you want to ensure sharpness throughout the image.

[Pieter]

At F22 nothing is sharp, so it doesn't really make sense to talk about 'the range of sharpness' here.

[XKAES]

While diffraction is a concern, there are lots of full-frame lenses, especially telephotos and macros, that stop down to f32, in order to increase the very thin DOF at high magnifications.  Sometimes, DOF wins over diffraction.  And, just like DOF -- which is not simply IN-focus vs NOT-in-focus -- diffraction is a gradual scale, too.