Parts of image out of focus, even on the sharp focal plane?!

[dan_spellman]

<p>Hey there,</p>

<p>Its a little embarrasing to come across a focusing problem - I'm not exactly a beginner! But some portraits I took today have baffled me. All the conditions seem good for focusing, yet part of the image is quite soft...</p>

<p>I was shooting tethered full body portraits today with a D700 and the 70-200. I stayed on 70mm and the camera was on a tripod. I used autofocus on the subject and would then switch it to manual and leave it (for faster shooting). I was using an Alienbees strobe, camera on 125/sec at f8.</p>

<p>Most of the image - the models body and clothes, is perfectly sharp. But as you look higher from the body to face, things get progressively soft. At the top of the head its pretty damn soft! While we were shooting tethered, the fact that the body seemed in focus threw me off, and things look okay at 50%. But 100% they are pretty bad in the face, which I only see now after the shoot!<br>

<br />I would understand whats going on if NONE of the subject was in focus - presumably the camera backfocused or just focused in the wrong spot. But whats going on if your at f8, 80% of the subject is in focus but things get progessively blurry towards the head? I understand that if you focus on the subjects middle/torso at a big aperture, their feet and head might be out of focus. But I was at f8, and very far from the subject at 70mm! To add to the confusion, I shot a portrait of two people next to eachother under these exact same conditions a few days ago, and EVERYTHING is in perfect focus! Aargh!</p>

<p>Any suggestions appreciated! </p>

[JosvanEekelen]

Perhaps post a few examples?

[btmuir]

<p>Yes, without examples it's hard to say but I can suggest perhaps the lens was dropped and one or more of the glass elements got decentered.</p>

<p>Take a shot of a flat surface like the proverbial brick wall and see what it looks like.<br /> You could try stopping down and see if it gets better.<br /> Test at various ranges of the zoom.<br /> Was this a rental lens?</p>

[Matt Laur]

<p>Which verison of the 70-200 are we talking about, and how close to the edge of the frame is the subject's face? And, how high is the camera positioned, relative to the subject's face (waist level? eye-level?) - which might help us to understand the whole scenario.</p>

[Alan Marcus]

<p>Without seeing examples, all one can do is guess your depth-of-field that was too shallow. Likely, you will be told to check depth-of-field charts and on-line calculators but these offer little value in the heat of the battle.</p>

<p>Now most understand that depth-of-field is that zone that remains acceptably sharp. It extends fore and aft from the point focused upon. You need to know how to expand this zone.<br>

1) The greater the camera-to-subject distance, the wider the zone.<br>

2) The shorter the focal length, the wider the zone.<br>

3) The smaller the aperture setting, the wider the zone. (f/8 is not applicably small, f/16 or f/22 is small).</p>

<p>Likely, the factoid you need:</p>

<p>The zone of depth-of-field is not split down the middle. The zone extends further to the rear. As a rule-of-thumb, the zone of acceptable sharpness extends 2/3 away from the point focused upon and 1/3 back towards the camera. As an example, say your camera is focused at 12 feet, aperture f/8.</p>

<p>The zone is 2 feet 8 inches wide. It extends 10 feet 10 inches to 13 feet 6 inches.</p>

<p>If the camera is reset to f/16, the zone becomes 5 feet 7 inches wide extending from 9 feet 8 inches to 15 feet 5 inches.</p>

<p>What I am trying to say is, best to use tiny apertures to gain depth-of-field however since the zone extends both fore and aft, try shifting your focus point a litter further to the rear. If you focus on the torso, stuff in front of the model would be in-focus but noting is there. If you focus a little further back, the stuff you want in focus will be incorporated in the zone of acceptable sharpness. </p>

<p> This is not a situation where tables and charts will be of great help. This is a case of practice and using your noodle.</p>

[craig_shearman1]

<p>What point did you actually focus on? The eyes? Chest? Stomach? In photographing people the standard practice is to focus on the eyes. So in theory you should have had sharp eyes and other points out of focus. Sounds like you were focusing on some other part of the body, which might be several inches closer to the camera, depending on angle and pose. Also sounds as if the camera were low and pointed upward. Distance from lens to stomach, for example, might be considerably shorter than lens to face.</p>

[William Michael]

<blockquote>

<p>I was shooting tethered <em><strong>full body portraits</strong></em> today with a <em><strong>D700</strong></em> and the 70-200. I stayed on <em><strong>70mm</strong></em> and the camera was on a tripod. I used autofocus on the subject <em><strong>and would then switch it to manual and leave it</strong></em> (for faster shooting). I was using an <em><strong>Alienbees strobe</strong></em>, camera on <em><strong>125/sec at f8</strong></em>.<br /> Most of the image - the models body and clothes, is perfectly sharp. But as you look higher from the body to face, things get progressively soft. <em><strong>At the top of the head its pretty damn soft</strong></em>! . . . But whats going on if your at f8, 80% of the subject is in focus but things get <em><strong>progessively blurry towards the head?</strong></em></p>

</blockquote>

<p>My best guess is the Subject's Head moved and you have used 'set and forget' manual focus.</p>

<p>A sample image or two would assist especially to show how close the head is to the top of the frame but it is really easy to make a scenario whereby the DoF would be small enough to render the head quite soft.</p>

<p>D700; 70mm; Full Length Portrait (Standing), Vertical Orientation; F/8<br /> → SD ≈12~14ft<br /> → DoF ≈ 2’10”~4’ (CoC = 0.02mm)</p>

<p>At that short SD with a 70mm lens, the DoF is spread approx 1:1.<br /> Therefore you’ve got about 1’5” to 2’ DoF behind the Plane of Sharp Focus with which to play.</p>

<p>IF the camera’s elevation was at a about or a bit lower than belly-button height and the SD ≈ 12’<br /> → Distance to head (in centre of frame) ≈ 12’7”<br /> → Distance to head (about 1’6” off centre of frame) ≈ 12’9”<br /> The head could easily be 9” beyond the plane of Sharp Focus.</p>

<p>The head could be even more behind the Plane of Sharp Focus if the Head were farther toward the side and/ or if the head were slightly tilted backwards – note that even a slight incline of the head can move the eyes backwards by 5 to 8 inches . . .<br /> <em>in an instant you could be at the edge of the far limit of the DoF </em><strong><em>just because of a small movement of the Subject's Head. </em></strong></p>

<p><strong><em>My suggestion is (as a general rule) to focus (on the eyes), for each portrait shot.</em></strong></p>

<p>WW</p>

[jeff_schraeder1]

<p>All of the above advice is very good. One thing I might add is that the focal plane is always parallel to the film or censor plane. If you camera is tilted up or down or left or right the focal plane will also be shifted.</p>

[plasma181]

<p>I bought a 35mm SLR about 8 years ago. Soon after I bought it, I got curious about the shape of the area in focus. Is it a plane or a sphere. In other words, say I focus my lens 5 feet in front of me. What will be in focus? Everything in the plane 5 feet in front of the lens regardless of distance, or everything in the sphere drawn 5 feet from my lens? ( Does this make any sense? ) </p>

<p>I conducted a few experiments and found that the shape of the focus area is indeed a plane. If 10 people were standing side by side, and you took their picture, the people on the ends would be farther from your lens than the people in the center, but they would all be in correct focus. </p>

<p>As for this problem; if your camera is looking straight ahead so it is neither pointing up or down, you should be able to take a standing portrait with everything in focus. If there is tilt to the camera, some parts of the subject may be out of focus. </p>