Why are my pictures blurry even though a DOF calculator shows everything should be in focus?
Short answer (TL;DR): Because you're viewing them at much larger magnification than the viewing conditions assumed by the Depth of Field (DoF) calculator you're using. Also, because infinity focus and hyperfocal distance don't mean what you seem to think they mean. They are not the same thing and aren't accomplished by using the same focus distance.
The question and comment by the OP demonstrate a basic lack of understanding between the difference in infinity focus and hyperfocal distance. They are not the same thing. Far from it. They also demonstrate a lack of understanding about how display size and viewing distance also affect depth of field.
Infinity focus does not mean an infinite depth of field (DoF) in the sense that everything from the camera to infinity is in focus. It means the point of sharpest focus is infinity - the lens is focused on light from point sources of light that are far enough away that the light rays are striking the lens as
collimated light. Anything closer to the camera than infinity will be out of focus to one degree or another. The closer it is to the camera, the blurrier it will be.
For landscape photography what is often desired is to place infinity at the very rear of the DoF. This is often referred to as the hyperfocal distance. Rather than placing the point of sharpest focus at infinity, it is placed at a nearer distance calculated to just include infinity in the DoF.
In order to understand this difference one must first understand what depth of field is and, more importantly, what it is not.
In a way, depth-of-field is an illusion. There is only one plane of sharpest focus. Everything in front of or behind the point of focus is out of focus to one degree or another. What we call DoF is the area where things look, to our eyes, like they are in focus. This is based on the ability of the human eye to resolve certain minute differences at a particular distance. If the slightly out-of-focus blur is smaller than our eye's capability to resolve the detail then it appears to be in focus.
When you magnify a portion of an image by making it larger or moving closer to it you allow your eye to see details that before were too close together to be seen by your eyes as separate pieces of the image. There is no magic barrier beyond which everything is equally blurry and inside of which everything is equally in focus!
Since things are gradually blurrier in a photo the further they are from the point of focus, as one gradually increases the magnification at which the image is viewed the perceived depth of field gets shallower as the near and far points where one's eyes can discriminate fine details move closer to the point of focus.
If you want an object a few feet in front of your camera to be sharply in focus, you need to focus on that object, not on infinity.
The other thing you seem to be missing is that the vast majority of DoF calculators are based on some often unspoken assumptions about viewing conditions:
Perhaps a lot of the confusion stems from the unstated assumptions
used by many Depth of Field calculators. They make assumptions about
viewing size, viewing distance, the viewer's vision, and the size of
the image sensor or photographic negative. If most users of DoF tables
and calculators are not aware of the assumptions in place it's easy to
understand how the idea that DoF is an intrinsic quality of an image
apart from viewing conditions has gained so much traction.
For many years during the 20th century the assumptions were an 8x10"
print viewed at a distance of 10" by a person with 20/20 vision. Some
DOF calculations, such as those used by lens manufacturer Zeiss,
assumed the viewer had 20/15 vision! As is stated above, any time any
of those variable are changed the perception of DoF in the same image
is altered.
In the current environment, most of those assumptions are no longer
applicable. We routinely view images at sizes ranging from near
postage stamp size on our portable electronics to the various sizes of
our computer monitors to large screen televisions viewed from fairly
close distances, to billboard sized banners not always viewed at
typical billboard sized viewing distances.
When we view them on our computers we even change the DoF depending on
whether we choose to view the entire image scaled to fit our screen or
whether we choose to view one piece of the image zoomed in to "100%"
where each pixel of the image is depicted by a pixel of the screen we
are using. If part of a 24 MP image is viewed at 100% on a 23" HD
monitor with 1920x1080 resolution that's the equivalent of seeing the
entire image displayed at 60x40 inches! If we view a 50 MP image on
the same monitor we're looking at a small piece of a 125x83 inch
display size of the 50MP image! Since we've more than doubled the
amount of enlargement applied to an image viewed from the same
distance we've also effectively halved the DoF of the larger
resolution image compared to the lower resolution one if they were
both shot under the same conditions: sensor size, focal length,
aperture, and subject/focus distance.
One online DoF calculator that does allow changes to viewing
conditions is found at Cambridge in Color. To get the additional
options please click on the "show advanced" button.
When viewing a 20MP image at 100% on a 27" monitor you will be viewing the equivalent of a piece of a 68x45" print! That is 7 times larger in linear terms than the 8x10" assumption of your DoF calculator. Therefore the perceived DoF will be 1/7 as deep as it would be if you were viewing the same image at 8x10" from the same viewing distance!
Since depth of field is defined as the area on either side of the point of focus within which things are acceptably sharp, what is acceptable changes as we alter the viewing conditions. What is acceptably sharp at 8x10" will often not be acceptably sharp at 68x45", or even 16x20".
In the example quoted in the original question above, the DoF calculator returned a hyperfocal distance result of DoF from 2m to infinity at f/3.5. It's not clear whether that result was when the lens is at 10mm focal length, 20mm focal length, or another focal length in between. Whichever the case, that result is only attainable if the lens is focused at 4m. Then everything from 2m to infinity will be acceptably in focus when viewed at the display size and viewing distance assumed by the DoF calculator. But if the image is viewed at a much larger size the DoF must be recalculated based in the increased magnification, and the resulting narrower DoF will mean the hyperfocal distance will be pushed further away from the camera.
From the comments:
'Why does the calculator not correspond with real life' because every time I try to focus using the numbers the stupid calculators spit out, my pictures and up being blurry.
Because in real life you are not viewing the photo under the same enlargement ratio that was used by "...the stupid calculators..." to calculate the hyperfocal distance. When you view the exact same image at approximately 68x45" it will not have the same DoF as when you view that image at 8x10" or 8x12". There are DOF calculators that allow the user to input the anticipated display size. This one, already linked above, is one such resource.
If you display your picture using only an 8x10" area of your monitor then the calculated results may apply. Since you haven't told us the resolution of your camera or the resolution/pixel pitch of your 27" monitor we don't even know what the enlargement magnification is when you are viewing your images at 100%! But it is probably around at least 8-10 times as much as an 8x10 would be! That means the field of acceptable focus on either side of the point of focus will, at most, be one-eighth to one-tenth as deep as it would be were you viewing the same image at 8x10".
I focused to infinity using the calculators (it says I should focus at something that's 2m away to go get a DOF of infinity behind my subject) online and it wasn't sharp (the foreground, the subject and the background). I also focused to infinity using the lens' infinity mark and it wasn't sharp either.
and
Maybe I should put it this way: According to the calculators, If I focus at the hyperfocal distance, my DOF is 'infinity' but it is also 'infinity' if I don't focus at the hyperfocal distance, say, 2 or more meters. And the acceptable sharpness in the foreground only changes a few cm. So, in theory, it shouldn't matter what I focus on, it's always infinity. How can this be?
When you focus on a hyperfocal distance (calculated for a specific focal length, aperture, and magnification ratio that is affected by sensor size, display size, viewing distance, etc.) you aren't focusing on infinity. You are focusing on a nearer distance that includes infinity on the very edge of what will be acceptably sharp (and NOT as sharp as what is in focus) before you will begin to perceive blur based on the variables you have entered into the DoF calculation. If any of those variables (such as display size, viewing distance, etc.) change then the calculation must be refigured using the new values for the changed variables.
I watched some landscape tutorials and they all focus manually using live view. One tutorial just focused at infinity and their foreground was sharp. I don't know how this can be.
Were you viewing the images in the tutorials at full resolution (20+ MP) at 100% on a 27" monitor? How did the DoF hold up under such viewing conditions?
As the answer points out (and the answer to another question that is linked in this answer goes into greater detail explaining), DoF is not an intrinsic property. "There is no magic barrier beyond which everything is equally blurry and inside of which everything is equally in focus!" How an image is viewed (display size, viewing distance, even the eyesight of the viewer) all affect the DoF of the same picture. If your DoF calculator assumes "standard viewing conditions" then when you blow it up to 100% on your 27" monitor the results the calculator gives you will not be applicable.
When setting my lens manually on the hyperfocal distance for a given focal length and aperture it should be acceptably sharp right? Technically I shouldn't need to focus using the viewfinder or live view if the lens is calibrated accordingly, right?
That all depends on how well calibrated the markings on your lens are. The number of current lenses you can accurately focus using the markings, if the lens even has any, are very few to none. Most newer prime lenses, even very expensive ones, aren't usually marked that accurately. With zoom lenses all bets are pretty much off because unless the lens is parfocal (If the zoom lens is less than about $10K or up it very likely is not truly parfocal) the focus position for a particular distance changes as the focal length changes. For more about nearly parfocal lenses please see: Why does this lens lose focus when you zoom in but not when you zoom out? and Why are so many kit-lenses parfocal if it's an expensive feature?
And since the focus distance scales aren't that accurate, don't even start on the DoF scales!
I edited my post and added pictures. It's not about viewing size at all. I apparently can't get the focus right and when comparing the numbers from the DOF calculators with what my outcomes, something doesn't add up. For instance, when looking at professional landscape pictures I can zoom in all the way and everything in the foreground is razor sharp and the background is acceptably sharp. When doing the same with my example pictures, it gets blurry before I even reach 100% zoom. My gear should be good enough to create really sharp pictures for the internet(wallpapers etc.).
DoF is always affected by viewing size. But what you're talking about now isn't just DOF. It's sharpening, detail enhancement and other post processing steps that must be made to get what you're after. But you've also got to start with very good optics. And if you want to see a sharp image at 100% viewing you can't shoot at f/11 on a camera with a DLA of f/6.9.
