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Old Apr 19, 2009, 12:01 PM   #1
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There is just something that goes beyond my understanding in trying to shoot flowers, bees on flowers, etc. I read posts here daily and it is my understanding that the lower the f-stop # the better. My camera is a Kodak P850 which has alot of manual controls and I bought hoping I could get better pictures but except for longer focal lenght I think my 4X Kodak Z730 takes as good if not better pictures (just a little slower). The 35mm equivalent of the P850 is 36 to 432 (12X). The aperature starts at 2.8. My main questions are why does a dslr with an aperture kit lens starting at 3.5 do better in blurring the background than my lens that starts at 2.8? Is it strictly due to sensor size? My 2nd question is how can I get the background to blur with my camera which I know is difficult being a P&S? What settings would you recommend assuming it is taken outside with good lighting. It doesn't blur when I use the scene mode for flowers and I have made various other attempts unsuccessfully. Any guidance and help would be appreciated. Thanks.

Bob
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Old Apr 19, 2009, 1:10 PM   #2
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bob1841 wrote:
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There is just something that goes beyond my understanding in trying to shoot flowers, bees on flowers, etc. I read posts here daily and it is my understanding that the lower the f-stop # the better. My camera is a Kodak P850 which has alot of manual controls and I bought hoping I could get better pictures but except for longer focal lenght I think my 4X Kodak Z730 takes as good if not better pictures (just a little slower). The 35mm equivalent of the P850 is 36 to 432 (12X). The aperature starts at 2.8. My main questions are why does a dslr with an aperture kit lens starting at 3.5 do better in blurring the background than my lens that starts at 2.8? Is it strictly due to sensor size?
Yes.

bob1841 wrote:
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My 2nd question is how can I get the background to blur with my camera which I know is difficult being a P&S? What settings would you recommend assuming it is taken outside with good lighting. It doesn't blur when I use the scene mode for flowers and I have made various other attempts unsuccessfully.
The only thing you can do togettheshallowest possible depth of field is to use the largest possible aperture (the numerically smallest f-number.) Use A Mode, and keep the aperture as wide a possible.
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Old Apr 19, 2009, 1:26 PM   #3
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Thanks, TCav, I really appreciate it. I guess I will eventually have to upgrade.

Bob
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Old Apr 19, 2009, 2:53 PM   #4
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bob1841 wrote:
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... My main questions are why does a dslr with an aperture kit lens starting at 3.5 do better in blurring the background than my lens that starts at 2.8? Is it strictly due to sensor size? ...
Strictly - no. It is due to the difference in focal length of the lenses: real focal length, not 35mm equiv. Since the focal length and sensor size are tightly related, it can be said that it is due to sensor size, but that is not strictly true.

If you want to pursue the issue further, Google "circle of confusion" (with quotes) to look at the math
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Old Apr 19, 2009, 5:03 PM   #5
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BillDrew wrote:
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bob1841 wrote:
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... My main questions are why does a dslr with an aperture kit lens starting at 3.5 do better in blurring the background than my lens that starts at 2.8? Is it strictly due to sensor size? ...
Strictly - no. It is due to the difference in focal length of the lenses: real focal length, not 35mm equiv. Since the focal length and sensor size are tightly related, it can be said that it is due to sensor size, but that is not strictly true.

If you want to pursue the issue further, Google "circle of confusion" (with quotes) to look at the math
And the other variable is subject distance. Get close to the subject and allow distance from the background. You should be able to see blurred backgrounds at true macro distances.

Greg
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Old Apr 19, 2009, 6:06 PM   #6
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BillDrew wrote:
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bob1841 wrote:
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... My main questions are why does a dslr with an aperture kit lens starting at 3.5 do better in blurring the background than my lens that starts at 2.8? Is it strictly due to sensor size? ...
Strictly - no. It is due to the difference in focal length of the lenses: real focal length, not 35mm equiv. Since the focal length and sensor size are tightly related, it can be said that it is due to sensor size, but that is not strictly true.
See Wikipedia'sDOF vs. format size.
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Old Apr 19, 2009, 6:54 PM   #7
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TCav wrote:
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BillDrew wrote:
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bob1841 wrote:
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... My main questions are why does a dslr with an aperture kit lens starting at 3.5 do better in blurring the background than my lens that starts at 2.8? Is it strictly due to sensor size? ...
Strictly - no. It is due to the difference in focal length of the lenses: real focal length, not 35mm equiv. Since the focal length and sensor size are tightly related, it can be said that it is due to sensor size, but that is not strictly true.
See Wikipedia'sDOF vs. format size.
DOF is a lens property. The only influence outside of the lens is the circle of confusion, and that, as formats are concerned, has the opposite effect of what is expected. The lens focal length, however, dominates the equation.

Given the same focal length lens, the DOF is LESS with the small format. The big format will have a deeper DOF at the same aperture.

Greg
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Old Apr 19, 2009, 7:56 PM   #8
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Forget focal length. For the same angle of view, a larger image sensor has a shallower depth of field.

A 100mm lens on a Canon 5D (FF) at f/16 focused at 10 feet has a total depth of field of less than 3 feet. A 50mm lens on an Olympus E520 (4/3) at f/16 focused at 10 feet has the same angle of view, but a toal depth of field of over 6 feet.

Using the focal length and the circle of confusion is going around the block to get next door.
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Old Apr 19, 2009, 8:22 PM   #9
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Bob, your question: My 2nd question is how can I get the background to blur with my camera which I know is difficult being a P&S? What settings would you recommend assuming it is taken outside with good lighting. It doesn't blur when I use the scene mode for flowers and I have made various other attempts unsuccessfully. Any guidance and help would be appreciated. Thanks.

There are, I believe two macro settings for your camera, Wide and Tele. In Wide, you will be able to get closer to your subject, but the DOF is so large at the short focal length, that nearly everything will be in focus. At the Tele setting, you should be able to get a reasonably blurred background. You will need to be a bit further from your subject, though, and it helps to have some separation distance from the background.

brian


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Old Apr 19, 2009, 8:28 PM   #10
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TCav wrote:
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Forget focal length. For the same angle of view, a larger image sensor has a shallower depth of field.

A 100mm lens on a Canon 5D (FF) at f/16 focused at 10 feet has a total depth of field of less than 3 feet. A 50mm lens on an Olympus E520 (4/3) at f/16 focused at 10 feet has the same angle of view, but a toal depth of field of over 6 feet.

Using the focal length and the circle of confusion is going around the block to get next door.
One way of looking at it if you want to completely ignore the field of optics - which would be a very strange thing to do when talking about lenses. Would be interesting to see where you could find any information about depth of field that included more than the focal length, the circle of confusion, f/stop, and subject distance. If you want to get silly I suppose you could recast that in terms of field of view, f/stop, subject distance, circle of confusion, and format size. But why would you want an equation with five variables when four will do very nicely? And note that there is no way to avoid including the circle of confusion.

It is also interesting that the Wiki article you quoted has the equations for calculating the depth of field - and those do not include the format size. As I noted, and the Wiki article notes, there is a very tight relationship between format size and focal length to capture the same field of view. So it is reasonable to say that format size influences depth of field even though it is not strictly true. And it is overly complicated to cast it in terms of format size.

It should also be noted that larger formats/longer lenses allow smaller f/stops before diffraction rears its ugly head. So a large format can achieve a comparable DoF at the expense of longer exposure times.
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