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Probably a novice question, but how do I correctly diagnose from a photo for what reason that camera wasn't able to focus properly?

It can be any 1 of the following

  • Unsteady hand
  • Lens issue
  • Metering
  • Re-Calibration required in camera
  • or ...

Is there a set of unsaid protocols that needs to be followed by a photographer?

Goal is to get a sharp and crisp image prior to editing.

[PS: I own a Nikon D5200.]

  • 1
    This is highly situation-dependent. (Handheld? Macro? Single or continuous AF? What's the light level? Etc.) Are you looking for a sort of canonical flowchart going through all such possibilities, or do you have a specific situation you want to resolve? – mattdm Mar 13 '17 at 18:09
  • Here's an example: There's an old man and I handheld to focus on his eyes with 50 mm lens. But when I zoom in to check, the focus isn't right. I have an understanding of basics and worth mentioning is that this doesn't happen on d5100, but frequently on d5200. – MnZ Mar 13 '17 at 18:18
  • please attach image you think is "unsharp" – aaaaaa Mar 13 '17 at 18:48
  • In your example, how are you focusing on his eyes? Manually focusing, or with a single AF point, or ? – MikeW Mar 13 '17 at 20:00
  • Single AF point on the eye – MnZ Mar 13 '17 at 20:05
8

The question is extremely broad. There are a lot of questions and answers here that address particular aspects of blurry pictures. Putting all of that in one answer would be excessively long as well as redundant. I've grouped many of them under different headings and provided links to other questions and answers here at photography at stack exchange.

Is your camera moving during the exposure?

Probably the number one reason for blurry pictures is camera motion. The sharpest images are those taken with the camera immobilized on a solid mount, usually a tripod. That isn't always possible, though. When shooting with the camera handheld good camera handling techniques and proper shutter times are vital.

How much does a camera move in 1/250 of a second?
At what shutter speed threshold does a tripod start to matter?
How can I determine the minimum shutter speed to avoid blur from camera shake?

Image Stabilization can help with camera motion in certain situations, but IS/VR/VC/etc. has limits to what it can do.

Just because you think the camera is missing focus doesn't mean that is what is causing blurry pictures: How can I more consistently focus on the point I want?

Is your subject moving?

This can affect your shot in two ways:

  • The AF system may have difficulty tracking a moving target and the focus is missed.
  • The subject motion may be significant enough during the exposure to allow blur.

IS/VR/VC/etc. does nothing for subject motion.

Why my "action" shots are blurry even shooting on AF-C, is this a lens or camera limitation?
Focus problem vs. motion blur vs. camera shake - how to tell the difference?
What went wrong with this concert photo and what could I have done to make it better?
How can I avoid this blur during taking indoor party pictures?

Are you giving your camera's AF system enough light/contrast to focus?

PDAF (viewfinder) and CDAF (Live View) both require contrast to successfully focus your lens. If the combination of low light and a narrow lens is pointed at something with low contrast, the AF system won't perform well, if at all.

What could be causing focus problems in low light?
How can I focus quickly outdoors in the dark?

Are you really telling your camera to focus where you think you are?

With pretty much any modern AF system the areas of actual sensitivity are larger than the little markers for each AF point that you see in your viewfinder. The good news is that each one covers a larger area than you think. The bad news is that each one covers a larger area than you think. If your target is very small but there is an area of even greater contrast within the area of sensitivity, the camera will almost certainly focus on the area of greater contrast. For a look at how this works out practically when shooting, see this entry from Andre's Blog. For a look at how AF accuracy can vary from shot to shot, see this entry from Roger Cicala's blog at lensrentals.com.

Although there are a lot of similarities between various PDAF systems, they all have their own "map" of areas of sensitivity for each AF point. They all have different degrees of sensitivity for various AF points and maximum lens apertures. In order to master any of these AF systems, practice is required! It's not enough for you to know where you think you are telling the camera to focus. You have to learn to speak the camera's language and see the scene in the viewfinder the way the AF system does.

How can I effectively use the focus points (of Canon DSLR), to get accurate focus on a small subject?

Is your lens focusing where the camera told it to?

Sometimes slight front or back focusing issues caused by the manufacturing tolerances of the camera and lens match up fairly well and they cancel each other out. At other times they compound upon each other. Autofocus micro-adjustment can help to match the lens to the camera. Be sure you're doing the testing and adjustment correctly, though, or you can make things worse.

Do the issues with sharpness I am seeing require AF fine-tuning?
Which offers better results: FoCal or LensAlign Pro?
What is the best way to micro-adjust a camera body to a particular lens?
Does this test chart show that my kit lens front focused?
Fine tuning a lens focus

Are you using best technique and AF practices in challenging shooting environments?

I'm having trouble getting sharp pictures while shooting a concert from a press pass location
Pictures of dancers on stage
Why isn't my DSLR focusing accurately on a fast-moving subject?
How to focus on fast moving objects with a low-end dslr?
Canon 7d & 24-70 ii - can't get a crisp or well exposed shot

Are you sure the photo is blurry at all?

Sometimes other issues, such as improper exposure or poor white balance settings can make a properly focused image look blurry. Fixing the exposure or WB can often show the image was more infocus than it first appears. In challenging light be sure to save the raw data, it can allow you to draw out more detail than an in-camera produced jpeg will begin to show.

Blown out blue/red light making photos look out of focus
How to cancel purple stage lighting on subjects?
Lots of noise in my hockey pictures. What am I doing wrong?

Have you reached the limits of your camera/lens' capabilities?

How can lens cause consistent front or back focus?
How can I effectively use the focus points (of Canon DSLR), to get accurate focus on a small subject?
Does autofocus work better with f/2.8 lenses vs f/4 or slower?
Canon 24-70mm 2.8f - Optimal aperture for sharper pictures
How can I best utilize a point-and-shoot for concert photography?
Why is in-camera stabilization not popular?

For more regarding various causes of blur in photos, please see:
What causes blurred/non-sharp images taken of stable objects?
Why are my football action shots blurry?
How could I achieve stock quality sharpness?
Why are my photos not crisp?
If the focal plane is curved, should the outer AF points work correctly or front-focus?
Blurry pictures when zooming in

  • 1
    Hey @michael-clark! Thanks for the elaborate explanation and the references. I was actually looking for such an explanation. – MnZ Mar 16 '17 at 12:36
2

Since you ask a pretty general question I am going to try for a general answer, as this question is asked probably more than any other single question in many forums.

To figure out the issues you must become a bit of a detective. First, gather all the information you can. Among the things you should try to get are:

Lots and lots of samples, as one bad shot is very hard to diagnose in isolation. Then look for patterns in them, among such issues as below.

Failure to acquire focus will usually result in some area of the image being in focus, while desired areas are not. Look close at the background and foreground (grass and other textured surfaces are a good place to look). If you find a specific area in focus (but not the one you want), you can (mostly) eliminate vibration or motion issues.

Look for motion. For subjects, see if stationary subjects (or ones that match your panning) are in focus while others are not. Look for smearing - does the blur you see seem directional - looking at points and lines in different orientation will help you. If you see a consistent smearing in one direction, that is most likely motion of the subject or the camera.

It is worth noting that motion blur can be difficult to see, especially camera shake. It might just appear as a blur. Also do some tests with support - tripod, monopod, bean bag - whatever is appropriate. Take some shots with a timer so your hand is not even involved. See if these result in less blur than your hands.

Carefully looking at the two issues above will usually help distinguish failing to acquire focus from motion blur.

Another cause is equipment vs. expectations. It is always worth getting a perfectly in-focus shot with your equipment so you know what it can do. Cameras with live view are easiest - put it on a tripod, use a zoomed-in live view image to focus very carefully in manual mode for a stationary object, and take a shot. Take a few. You must use live view, never the viewfinder to focus, as live view is the real sensor data. Because this eliminates the auto-focus mechanism all issues of back/front focus and such are eliminated. If the resulting shots are not clear (and you have been careful), suspect your expectations are not aligned with your equipment. Be sure to check multiple lenses, with and without filters (I often see really cheap, poor filters on really nice lenses). Know what your equipment can do, to judge against what it does routinely.

Metering and light can be an issue but would be at the bottom of my list for concerns. Really high ISO shots will be blurred a bit by noise, and conceivably you may be in an area too dark for your AF mechanism to work. But frankly you would likely already know that, the effects are not that subtle. White balance and exposure per se has no real affect on focus.

Post processing can also be an issue. Some people will shoot raw, and then apply no sharpening at all. Most DSLR's need some level of sharpening just to reach "normal". Experiment a bit, if you post process, with sharpening settings, and if not with the in-camera controls. But again, I would put this closer to the last things to worry about.

Now... where you go from here depends on what you find. Probably (sadly) you will find some of all of these issues, since humans are involved as well as imperfect equipment. But gather a lot of data and see which area you most need to work on, then research it, or ask about it, with some specifics. I cannot begin to address each possible cause in one answer as my fingers will wear out.

But... you will be continually frustrated (especially when asking for help) if you just use a shot at a time, as there are so many possibilities. You need to be aggressive at experimentation and collecting samples to see where the patterns are. Since you cannot go back and time and fix any one photo, your goal should be to figure out where your most prevalent problem lies, and fixing it by changing what you do, then move on to the next.

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