Help sorting out DOF issues (long)

Started Aug 30, 2012 | Discussions thread
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Steve Ridges
Senior MemberPosts: 1,015
Help sorting out DOF issues (long)
Aug 30, 2012

Hi everyone. I'd like help sorting out some issues I had while shooting my sons soccer game. I used my D800 and 70-200 VR1 lens. I realize that the images are a little hot (I dialed in -.3EV later in the game) and that the composition is not the best (I tried to keep the center focus sensor over the kids as its the most accurate. 36MP allows me to crop later to account for the rule of thirds etc.)

I initially started shooting at F/2.8 because I wanted to blur the distracting background but quickly found that I didn't have enough DOF. I'd get my sons hand or foot in focus but not the face. I then switched to F/4 and F/4.5. According to my caclulations, at 200mm with a subject distance of around 50+ feet, that should produce about 5' of DOF. I ran into a couple of issues with this.

First, in cases where it did work, the child is in focus and everything behind them is out of focus. Do different lens provide "more out of focus" then others? When I search the web for soccer pictures, I find lots where the crowds etc. are VERY blurred out. In my case, the background is soft but still sharp enough to distract from the pictures. As I said before, I can't open the aperture up more because I won't have the child in focus. For example, look at this picture (All pictures are the 9MP images that were part of my RAW + JPG small)

You can see from the grass that the DOF starts just before the kids and ends just after them yet you can still make out the chain link fence behind them. I expected the background to be much more blurry. Is this just a case of I need more space behind them? I'm sure in pro soccer, the fields are much bigger so the crowd would be farther away but the flip side to that is I'm able to shoot much closer than would be possible on a regulation field which should provide narrower DOF.

The second issue I had is there are several pictures where the kids feet are in sharp focus but their head is not. I'm struggling to figure out why this is. I assume the plane of focus is parallel to the film sensor. In some cases, I was standing and shooting down on the kids. This would slant the film plane so the top was further back then the front. Do you think this is what caused it? Many of the images where shot sitting in a chair so I don't think that is the case for all of them. If I were to shoot at F/5.6, I'd have more DOF to carry the head but I would make the first problem worse. Here's an example of a few shots where the feet are sharp but the head isn't. I wonder if this could be a problem with the lens aperture sticking and not closing all the way? I shot in Aperture priority so would the meter automatically compensate those cases with shorter shutter speed which is why the over all exposure is correct? My shutter speeds did stay fairly consistent at around 1/500 - 1/640. I had a few at 1/1000 but those were ones with the white shed structure in the background.

I realize that this post is not complaining about left AF sensors or Ken Rockwell and doesn't contain any cat pictures but if you guys could help me with my technique, I'd appreciate it.


Nikon D800
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