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Old Feb 9, 2006, 5:05 PM   #1
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Today I took this profile of a goose. Was surprised that it's beak was out of focus. Checked my focal points and noticed that I didn't have all the vertical points operating. Question: should that small bit of length from the lens make that much difference to place the beak out of focus?
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Old Feb 9, 2006, 5:16 PM   #2
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The terminology used to describe this is Depth of field, There shallow depth of field, which is what you used, meaning only a narrow part of depth is in focus, there is also completedepth of field which is in a picture where all or most of the depth is focused. A shallow depth of fieldhas apertures like f/2, or f/2.8 and an aperture for complete depth of field could be f/22, or f/32. Then there is moderate depth of field, which means that the focus area is completely sharp but the remainder is blurred, and the aperture for this is around f/5.6. Does this help at all?
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Old Feb 9, 2006, 5:22 PM   #3
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yes, it has more to do with your aperture than your focal points here. to get the complete head in focus you need more depth of field. to get more depth of field you need to step down your aperture. ie make it smaller or its f# larger. i.e. go from f5.6 to f11 etc. keep in mind that distance from subject and focal length also affect your depth of field. the closer you are, the less depth of field you have, so in macro you need to stop down to f22 or greater to get depth of field you need often. also, the longer the focal length, the less depth of field you have.

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Old Feb 9, 2006, 5:51 PM   #4
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Thanks guys for your coments. Iam well aware of Depth of Field. i.e. The greater the aperture # the greater the depth of field. However, my question was Question:should that small bit of length from the lens make that much difference to place the beak out of focus?

I was surprised that shooting a subject fromthat distance with a 300mm lens that the AV setting would be that critical. Probably the tip of it's beak is probably no more than 3" further from the lens as the side of it's head. So that brings up another question on this subject. From about 50' away froma subject using a 300mm 4.0L IS lens, what is the aperture tollerance to keep all parts of an object in focus? Is there some rule of thumb to follow?:?

Well no matter the mystery so to speak has been solved by all.:-)
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Old Feb 9, 2006, 6:49 PM   #5
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http://www.dofmaster.com/dofjs.html

The above link will take you to a depth of field calculator where you are able to put in your settings and camera model and distance and that will give you the acceptable distances of sharpness. The more wide open you shoot, the more narrow that area will be. Hope this helps.
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Old Feb 9, 2006, 7:19 PM   #6
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Thanks GoCubs that is a neat calculator at the site you suggested. I entered all the data as requested and it indicated that I should have had at least 3-4" of acceptable sharpness. So be it.

Here is another site on Depth of Field.

http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/950/depth-of-field.html
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Old Feb 9, 2006, 7:42 PM   #7
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You would think that would be plenty, be the goose may have moved an inch or so forward after the camera locked focus. Also, I'm not sure if the calculator in my link figures in the 1.5 "digital crop" by entering in your camera model. If not, you would need to enter in 450mm in the actual focal length which would make the DOF smaller yet. Best bet would be to close your lens down to around F8 if you have the light for it.
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