4

Context

So I know that Depth of Field (DoF) is controlled by your f-stop (aperture opening) of the lens in question.

Question

Is it possible to get birds completely sharp when they are so close (8.2meters) as I've seen in other shots? The bird was there for only a few seconds before flying away so I don't know if it's possible to Focus Stack that quickly when you're manually focusing for the bird's eye?

Below is a shot I've taken with my Sony a6000 with Nikon 300mm/f4 with 1.4x TC. Shutter speed 1/500 and ISO 1.2k. I see that the head/eye is completely sharp but the body, wings and tail are blurry, as if there's not enough depth of field.

Update

I forgot to put the aperture here. It was at f8. Exposure value was at 0. I've included a second shot there the focus was on the body leaving the tail/wings sharp but I don't know if that is "acceptable" for a bird that close.

Lens: 300mm f4 with 1.4 RC Head Focus ISO: 1.2k F/8 1/500 Body focus ISO: 2.5k F/8 1/500

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    As you say yourself it (also) depends on the aperture. But what aperture setting did you use? – null Feb 8 '16 at 15:44
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    For reasons of physics and optics, you only get "complete" sharpness in one specific plane; everything closer and farther is out of focus to some degree. It may however be "sharp enough" according to some particular metric. – a CVn Feb 8 '16 at 16:12
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    In this instance of your sample you could have afforded to stop down by a couple of stops. That probably would have given you the sharpness you're looking for. – James Snell Feb 8 '16 at 16:51
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    Considering how many of the highlights are fully saturated, stopping down would probably have improved exposure as well as DoF. – Michael C Feb 8 '16 at 23:56
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    This is one reason the canonical pose of a bird is sideways to the camera. It reduces the depth of field problem. – Ross Millikan Feb 9 '16 at 4:43
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but the body, wings and tail are blurry, as if there's not enough depth of field

Using a depth of field calculator like DOFMaster, it's easy to plug in numbers and determine how much depth of field you should expect. For example, for a camera like yours shooting at 300mm, f/4, and 8.2m from your subject, you can expect about 0.06m of acceptable focus in front of the focused spot and also 0.06m behind that spot.

From the look of your image, it appears that you have about 6cm of acceptable focus in the space in front of the head and beak. For example, the bird's legs and feet are nearly as sharp as the beak, and they must be 4-5cm in closer to the camera than the head is. Given that, it seems a safe bet that you shot this at your lens's maximum aperture of f/4.

The depth of field calculator also lets us try some other possibilities so that we can figure out how to improve this shot in the future. At f/5.6, your DoF in front of the focus point only increases to 8cm, but at f/8 it jumps to 11cm, which is closer to the range you'd need to make a bird of this size and in this position reasonably sharp. So, stopping down to f/8 is one solution. Since most lenses are a little soft when they're wide open, stopping down will also sharpen the overall image a bit. On the other hand, one of the things I like about your photo is the separation between the bird and the blurry background, and stopping down will give you less bokeh.

As already suggested, you're not using the part of the plane on the far side of the bird. Focusing on a point that's a little closer to the camera would help put more of the bird in the acceptably sharp zone, possibly at a loss of a little sharpness in the eye. If you want to go this route, aim for the middle of the bird.

Depth of field increases as the subject gets farther from the camera. Keeping your f/4 aperture, you can get the same bump in depth of field by increasing the distance to subject from 8m to 12m. I doubt you had time to move for this shot, but if you're willing to trade distance (and therefore subject size) for depth of field instead of using aperture in the future, that's an option. As a bonus, you're less likely to startle the birds from farther away.

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    It's even thinner.... The OP said it was a 300mm + 1.4TC. – Rmano Feb 8 '16 at 23:12
  • Thanks for the advice there. I had no choice but to manually focus on the bird before it flew away so I focused on the eye and went from there. I shot at f8 but I had a 1.4x TC to get as close as I can for optically with focal length and physically distance wise. – unsignedzero Feb 10 '16 at 15:07
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Yes, it's possible.

The depth of field beyond the subject is greater than the DOF in front of the subject. Having focused on the bird's eye you've wasted a major part of your possible DOF, because the subject (bird) is before your focus point and thus mainly out DOF. Approximately two thirds of your focus plane is "in the air" behind the bird.

Next time try to focus on some point which is in the front third of the object (f.e. bird's back or wings in this case).

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    The flip side of this is that the "acceptable" loss of sharpness is lower for the eye than for feathers -- and there will be some non-zero but hopefully acceptable loss of sharpness as @MichaelKjörling says in a comment on the question. In this case the head would be quite out-of-focus if you focussed on the tail. – Chris H Feb 8 '16 at 16:20
  • @ChrisH Well, focusing on the tail is too extreme, I agree. Focusing on the neck or "shoulders" would have made tail sharper but the eye would still be in focus. I hope. – Zenit Feb 8 '16 at 16:28
  • If it's sitting still long enough to focus on the neck I agree. I assume manual focus as my central focus isn't that tight. Also if the branch isn't moving in the wind. – Chris H Feb 8 '16 at 16:30
  • Using DoF Master, the 300mm + 1.4x on the APS-C A6000 focused at 8.2 meters gives a total DoF of .08 meters: from 8.16 to 8.24 meters. That's a 50/50 distribution (within the limits of 0.01 meters as the minimum unit of measure). – Michael C Feb 8 '16 at 23:50
  • The distribution of DoF in front of and behind the focus distance is highly variable as the focus distance changes. As focus distance decreases the distribution of the DoF between near and far approaches 50/50. At MFD many macro lenses reach 1:1 distribution. Even most non-macro lenses can get to within 49/51 at MFD. On the other hand, all lenses with infinity focus capability when focused past the hyperfocal distance distribute DoF at 1:∞. – Michael C Feb 9 '16 at 3:55

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