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I came across this article, and it says that if we focus at a hyperfocal distance, then everything from half of hyperfocal distance to infinity will be in focus. Then why don't we set the focus distance to be the nearest as possible, as this will achieve the maximum depth of field?

[EDIT]: I am concerned about the statement:

Using the aforementioned scenario involving a 20mm lens at f/11 on a full-frame camera, you get a hyperfocal distance of 1212 mm, or 1.2 meters (almost 4 feet). So you should focus on an object that is approximately 1.2 meters away; everything from 0.6 meters (half the hyperfocal distance) away to infinity will be in focus.

Assume that there are 3 objects, located at 0.4m, 1.2m, 5.0m. If I set the focus to the object at 1.2m, I will get 0.6m to infinity in focus, but the 0.4m won't be in focus. So the best would be to focus on the object at 0.4m, as it will cover 0.2m to infinity, which will cover all those 3 objects.

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    I don't understand what you mean by "nearest as possible" - the nearest to what? The hyperfocal distance is the point which achieves the maximum depth of field - any closer and points at infinity will no longer be in focus. – Philip Kendall Mar 11 '15 at 16:31
  • Take this statement as an example: Using the aforementioned scenario involving a 20mm lens at f/11 on a full-frame camera, you get a hyperfocal distance of 1212 mm, or 1.2 meters (almost 4 feet). So you should focus on an object that is approximately 1.2 meters away; everything from 0.6 meters (half the hyperfocal distance) away to infinity will be in focus. -- Then why don't I focus at the nearest object that falls into the frame? – rcs Mar 11 '15 at 16:32
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    But if you adjust focus to 0.4m, then you're no longer focused at the hyperfocal distance. Changing the focus doesn't change the hyperfocal distance for a given lens and aperture. – Dan Wolfgang Mar 11 '15 at 17:01
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    The hyperfocal distance is the nearest focus distance where infinity is still in acceptable focus. Focus any nearer, and infinity won't be in focus anymore. If, on the other hand, you're not interested in far away objects and only want eg. the three objects in your example in focus, by all means focus closer. – JohannesD Mar 11 '15 at 18:01
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    The article you cite assumes a circle of confusion of 30 µm, which is a very old standard suitable for the kind of fast grainy film photojournalists used in the previous century. Use this for landscapes on a high pixel count camera and you will almost certainly be disappointed. – Edgar Bonet Mar 12 '15 at 11:12
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Then why don't we set the focus distance to be the nearest as possible, as this will achieve the maximum depth of field?

Because it won't. If you focus on a point closer than the hyperfocal point, then the depth of field gets shorter. Infinity is no longer in focus.

So the best would be to focus on the object at 0.4m, as it will cover 0.2m to infinity

No, it would cover 0.3m to 0.6m. The depth of field quickly gets shorter when you focus on a point closer to you.

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Focusing at a point closer than the hyperfocal point loses the depth of field at infinity.

For example, if the hyperfocal point is 1.2m, and you focus at 1.2m, then your depth of field is from .6m to infinity. HOWEVER, if you focus at a point closer than 1.2m, say 1.0m, your depth of fields drop to between .55m and ~6m.

You can see the effects subject distance has on depth of field at websites like THIS one. Make sure to pick a full frame camera like the Nikon D4, D3x... option.

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If your objective is to get as much as possible of your subject in focus and you know in advance that most of your subject is beyond the half-hyperfocal distance then this may be helpful advice that simplifies the focusing process in setting up your shot.

However, there are at least a couple complicating factors:

  1. The hyperfocal distance changes with the lens focal length and aperture setting. So unless you are always shooting with the same focal length and at the same aperture setting, you need to be conscious of the hyperfocal distance for other combinations that you might use. The table below (from Brian Jansen Photography brianjansen.com) illustrates this.

enter image description here

  1. For many photographers, getting everything in focus is not what they want to do. Instead, controlling the depth of field in order to manage main subject and the negative space is most important. Your suggestion would not be helpful when this is the objective.

Understanding the importance of managing the main subject and the negative space can be summarized this way (from PhotographyMad.com):

When used properly, negative space provides a natural balance against the positive space in a scene. Getting this balance right is tricky and rather subjective, but it's something you'll get better at with time and practice.

with a photo like this one as a good example:

enter image description here

  1. A lot of photographs are not taken with short focal lengths and high f-stops. Using a telephoto is quite common for some photographers, even when shooting subjects that are relatively close. For example, shooting a night time soccer match from the sidelines may not work out well at f/11 with a "normal" lens. If you are shooting with a 200mm lens at f/5.6 then your half-hyperfocal distance is going to be 387 feet. Using your technique would make the whole idea of using that telephoto questionable, because you would have to stand very far back to keep the subjects in focus. In a case like this, you might be at the sidelines, where the subjects are much closer. They would be out of focus using this hyperfocal technique.
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The article you cite is not very good advice if you want great sharpness for landscape photography: it’s based on the concepts of depth of field and hyperfocal distance. These concepts are intended to help the photographer find the required aperture for getting barely acceptable sharpness across the relevant parts of the picture. What the author (like many authors) calls “circle of confusion” is actually the maximum acceptable circle of confusion. In its original sense, the circle of confusion is the size of the blur spot you would get from a point source: if it’s larger than the maximum size you can tolerate, then the image is not acceptably sharp. The key word here is acceptable. If you are after just-acceptable sharpness, these concepts are good. If you are after maximal sharpness (likely for the kind of landscapes shown as examples), they are not.

Assume that there are 3 objects, located at 0.4m, 1.2m, 5.0m.

In such a situation, if you want maximum sharpness, you have to focus at mid distance between the closest and farthest object, where “mid distance” is actually the harmonic mean of the distances:

                             0.4 m × 5 m
optimal focus distance = 2 × ─────────── = 0.741 m
                             0.4 m + 5 m

The harmonic mean is easy to estimate by just looking at the distance scale of your lens: it's exactly halfway between the 0.4 m and the 5 m marks.

Now you can estimate the circle of confusion that you will get at any subject distance with

N × c   │         1                1        │
───── = │ ──────────────── − ────────────── │
  f²    │ subject distance   focus distance │

where c is the circle of confusion, N the aperture number, and the vertical bars mean “absolute value”. This formula shows that, at f/11, both your furthest and closest object will be imaged with a 42 µm circle of confusion, which is not really that sharp. You have to stop down to f/16 if you want to stay below the canonical 30 µm limit. Stopping to f/22 will still increase sharpness, but stopping further to f/32 will reduce sharpness due to diffraction.

If you want maximal sharpness on both these objects, you will have to balance the blurring due to defocusing (gets better as you stop down) with the blurring due to diffraction (gets worse as you stop down). Rather than going through the math, I suggest you read Selecting the Sharpest Aperture by Ken Rockwell. I know the author is controversial, but in this particular instance the article is very sound.

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There's no sharp limit between in and out of focus. Everything but the focal plane at some exact distance is out of focus, it is just so slightly so that we don't notice it. There are two reasons why somebody would choose focusing further than the hyperfocal distance - the first being that when you focus exactly on something further than hyperfocal distance it will come out sharper than if you were to focus on the hyperfocal distance. Other times we just don't want the foreground in focus.

EDIT: I haven't read the last part of your question. The problem with that reasoning is that the depth of field is not constant. The closer you focus, the smaller the DOF is. At the hyperfocal distance, the DOF is infinite.

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not to restate what has already been said, but there are good apps for smart phones which calculate hyperfocal distance for you.

one app in particular i have for iphone that i would think be helpful to your understanding of this is called DOFmaster. you can plug in your focal length, f-stop, and select the HD button and it will produce your hyper focal distance for you.

alternatively you can select your camera subject distance and the app will provide you with your depth of field with a near limit and a far limit, to see how much depth you will have at that distance, aperture, focal length combination.

go ahead and plug in all those combinations you were asking about and you will see what happens to your depth of field when you change your focus point.

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