Tack sharp images

Let me preface this question by saying that I hope this is the right forum for this question. None the less here goes. Yesterday I was shooting bird images out my den window (window was open so no window glass to make a difference) of the many birds feeding around my feeder. I was using the following equipment: A Nikon D300, a Nikon 600mm f/4, VR lens, mounted on a Gitzo - G1325 tripod with a Wimberley Gimbal head. All the birds were smallish with the largest bird being the size of a Northern Cardinal. This is important only if the size of the target has something to do with it's sharpness. Speed of the shutter was over 1000 on each of the images. The birds were about 15 to 30 feet away from the lense. After taking about 120 images I downloaded them to my computer and was disipointed to find that the majority of the images were not tack sharp and I don't quite know why. I have used this lense for the past year with very good results, but at times I have had what I would call soft focus results. I tried both manual and auto focus and the results are the same-soft. I have carefully read and followed Arties advice on focus and although these have caused improvement in the sharpness of the images they are often still soft to one degree or another. I find that with large birds, such as swans, GBH, and eagles are much sharper. Could it have anything to do with the size of the bird, thus the size of the crop? I don't know whether this makes any sense at all. Should I lock up the mirror and try that? BTW I don't think the problem is camera related because I get the same general results when using my D3 or D700. I thought some time ago that it was because I shoot alot off a 'Artie Bag' on the automobile window, but I guess not. Anyway, if someone can give me some clues as to what I might try I would more than appreciate it.

Mac

Is the room heated? If so, the heat flare could be one reason that the images are not as sharp as you might expect.

You didn't mention the aperture that you were using. If there is enough light and the bird only 15 feet away, you could try to stop down to f/11 for a wider DOF.

Quote:

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Originally Posted by Wheeler McDougal Jr.

I find that with large birds, such as swans, GBH, and eagles are much sharper. Could it have anything to do with the size of the bird, thus the size of the crop?
Mac

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Size of bird shouldn't make any difference provided they are the same size in viewfinder (i.e same number of pixels covering the subject). Full frame image of a small bird should be as sharp as full frame of a large bird. If you are needing to crop the image to make a small bird bigger in the final image you will lose quality. I'm not sure that I am understanding you correctly on this though :confused:.

Hi Mac,

I shoot with the same lens and body a lot, with no issues.
At that close range, they should be razor sharp.
Please tell us some more information... mode, shutter speed, aperture, ISO, metering, focus point, etc.
Also, can you post a sample image?

Quote:

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Originally Posted by Wheeler McDougal Jr.

I find that with large birds, such as swans, GBH, and eagles are much sharper. Could it have anything to do with the size of the bird

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Auto focus is not perfect all the time. It does not work well under certain conditions. D300 manual page 70 talks about what situations AF does not work very well. Will yours be similar to one of those described? As for manual focus, how do you do manual focusing usually? If you rely on the electronic focus confirmation of the camera, that is also not reliable per here:

http://www.zeiss.com/photo


How about you post some of those soft images?

You can fine tune the AF on the D300 (a sub menu). I would check this by setting up a test on a static subject, adjusting the fine tuning from one shot to the other.

If you are shooting f4 and the birds are big in the frame, parts of the bird will be out of the sharp focus plane. So, using a smaller aperture (f8) would help.

Quote:

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Originally Posted by Wheeler McDougal Jr.

After taking about 120 images I downloaded them to my computer and was disipointed to find that the majority of the images were not tack sharp and I don't quite know why. I have used this lense for the past year with very good results, but at times I have had what I would call soft focus results. I tried both manual and auto focus and the results are the same-soft. I have carefully read and followed Arties advice on focus and although these have caused improvement in the sharpness of the images they are often still soft to one degree or another. I find that with large birds, such as swans, GBH, and eagles are much sharper. Could it have anything to do with the size of the bird, thus the size of the crop? .

Mac

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If you get even one "tack sharp" image, then you know that it is not a problem with the optics of the lens. It is some problem with technique. If you are shooting at 1/1000s, then shutter speed should not be a problem. You really don't need to have VR on at that high a shutter speed, so I would take some shots with VR off (if you have VR turned on). VR activation, especially if it is malfunctioning, can cause some vibration during activation. With my shoooting technique, I have AF uncoupled from the shutter button by a custom function. I have found that I need to AF, then half-press the shutter button to activate VR as I get ready to capture an image. I usually don't have VR turned on unless I'm below 1/500s.
Most likely the problem is some combination of depth of field and AF acquisition. A smaller bird enlarged in a frame will have greater magnification (and thus shallower depth of field) than a large bird filling the frame. If the AF sensor is on the body of small bird and you're shooting wide open, then the DOF may not include the eye of the bird. Also if the lens is back- or front-focuising slghtly, the error will be more visible with higher magnified subjects. So try shooting at a smaller aperture and slower shutter speed to get more depth of field.

Hi Wheeler: You could perform a simple test that I do with all my new lenses and lenses that have been repaired, due to my klutziness, at Canon Factory Service. I just take a piece of paper with some normal 12 point print and tack it to one of my deck posts outside with the sun behind my back. I stop the camera down to about 5.6 or so, lock everything down on the tripod and take an autofocus shot with my best lens technique. If the print on that sheet doesn't come back tack sharp, then there is a problem. You should even be able to see the little fibers around each letter when zoomed to 100%! Any time I've ever had doubts about equipment, this test has settled my nerves as my Canon gear always proves itself to be functioning perfectly as your Nikon probably will too. Good luck, my friend.

P.S. I know this sounds stupid but make sure you are not recomposing on those birds when you are in "constant focus" or Al Servo because your focus won't be locked. Just trying to think of all possiblilities.:)

I do this at home and agree with Axel that the problem is most likely heat waves. When I shoot from inside I shut the door to the room, turn the heat off and open the window. Then I come back in 30' and start. I want the room the same temp as outside. heat waves are insidious and will knock your focus out.

Thanks everyone for your toughts and I will try all your sugestions. Here is an example of what I was talking about and the settings I was using.
Nikon D300
600mm
900mm (in 35mm film)
1/800 sec, f/5
Mode: Av
Metering: Spot
Exp comp: +1/3
ISO: 400
AF mode: AF-C
White balance: SUNNY
Flash: Off
File size: 15.2MB
Image size: 4352 x 2868
Color space: AdobeRGB
Saturation: Normal
Sharpness: Normal
Contrast: Normal

Looks to me that the focus is well in front of the bird here and on the tip of the perch! Try fine tuning the AF, below is a link to a step-by-step procedure. Good luck!

Are you using center point focus? 9 point? 51 point? I like center point, as I can control the focusing better. The other focus point settings seem to grab the closer objects in the frame, as here with the tip of the perch.

http://photomatter.com/Reviews/NikonD300b.html

I guess it's the branches that distracted the AF system. I've found the AF can struggle when shooting small birds - especially not close by - with small branches around it. It's similar to one of the conditions in which AF doesn't work well, as described on page 70 of the manual.

Have you tried shooting a similar size stationery object with nothing nearby from a similar distance to see if the lens focus?

Wheeler, try using the center AF point only, focus on the bird's eye, lock the focus, then recompose and shoot. I would also stop down some. I usually try for F8 or smaller when shooting small birds that are large in the frame. Good luck!

Again- Thank you all for the help. I wanted to share with you a couple of other settings and an image that was suggested by Danny. Here are my settings on the AF Menus:
a1 - AFC-Release
a2 - AFS-Focus
a3 - Dynamic AF Area-21 points
a4 - Focus tracking-Short
a5 - AF Activation-Shutter/AF-On
a6 - AF Point Illumination-On
a7 - Focus point Wrap-Around-No Wrap
a8 - AF Point Selection-51 points
The rest of the sub-menus really aren't revelent.
The image I have submitted, was taken @ f/9, 250 sec., and is 12 point in size taken from a distance of a little over 21 feet and then the image was increased to 100%. I think you will agree with me when I say it is quite sharp, so I think the optics are just fine. If any of you have other questions as to settings or my techniques please feel free to ask and I will do my best to answer them.
Mac

Quote:

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Originally Posted by Wheeler McDougal Jr.

The birds were about 15 to 30 feet away from the lense.
Mac

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Isn't 15ft under the minimum focusing distance of the 600?

Yes it is.

Quote:

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Originally Posted by Wheeler McDougal Jr.

I think you will agree with me when I say it is quite sharp, so I think the optics are just fine.

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I would say there's nothing wrong with your system. I second Jim's suggestion: use one focus selector. Choose Single Point AF instead of Dynamic Area AF.

If you are regularly shooting at or near the minimum focusing distance, leave an extension tube on the camera.

In the example you posted, it looks like a missed focus as well as too narrow DOF.