Why are my family portraits blurry in bright light when using autofocus at f/4?
Asked 8/27/2014
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2 answers
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I shot a family event outdoors in strong late-afternoon sun. Exposure was manual, autofocus enabled, around 50mm, f/4, and a very fast shutter speed (about 1/3000s). Light levels were high, so camera shake and low light don’t seem to be the issue.
The main problem is that many images are noticeably out of focus, even though I focused on a person’s face and then recomposed. In one frame the image is sharp, but another taken seconds earlier with the same settings is not. In another example, a fence or background object appears sharper than the people, even though I did not intend to focus there.
What could cause this? Is it likely to be focus-and-recompose error, autofocus grabbing high-contrast background objects, depth of field being too shallow for a group at f/4, or possibly a lens autofocus/front-focus problem?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
11y ago
2 Answers
2
In the second image there's a metal-bar-looking-thingy right between the mother's and father's head that is very much in focus (at least it looks like that on the web-sized image) - so I would guess the AF focused on that bar and not the mother's face.
The area covered by the AF sensor is substantially larger than the rectangle you see in the viewfinder so it's highly possible that the AF system focused on that nice contrasty horizontal line when you aimed it at the camera-right eye of the mother.
I'm not sure why the fence in the 3rd image is so nicely focused but it's way too in-focus to be an AF error, it looks like the AF successfully focused on the fence, in an AF error usually nothing is in focus.
Also, I just want to mention that - while I don't think this is the situation in those images - the "focus & recompose" technique can cause focus problems on wide apertures because when you recompose after locking focus you are changing the distance between camera and subject, if you have shallow DOF and you focus on something at the side of the frame this change can throw the subject out of focus.
Originally by user2481. Source · Licensed CC BY-SA 4.0
user2481
11y ago
0
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Most likely causes are autofocus target selection and shallow depth of field.
At f/4, group portraits can be marginal if people aren’t on the same plane. If you focus on one face and recompose, that can also shift the plane of focus enough to miss, especially at 50mm and closer distances.
Your AF system may also be grabbing a higher-contrast object near the focus point. The actual AF-sensitive area is often larger than the box shown in the viewfinder, so objects like a fence or metal bar can attract focus even if you aimed at a face.
Since one image is sharp and another seconds later is not, with the same exposure, shutter speed isn’t the issue. 1/3000s is far more than needed to prevent shake here.
It’s also possible the lens/body combination has autofocus accuracy issues (front/back focus), especially if this happens repeatedly with that lens.
Try: use a single AF point placed directly on a face, avoid focus-and-recompose for groups, stop down more for extra depth of field, and test the lens for AF consistency. Also check whether a filter or viewfinder diopter issue is confusing evaluation.
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AI11y ago
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