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#11 | |||
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Join Date: Feb 2007
Location: Wisconsin
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TCav wrote:
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There is no doubt that a 100mm lens has less DOF than a 50mm lens at equal f-ratios. In absolute terms, you can also look at same DOF by going to f8 on the 4/3 lens. In other words, not only is it a lens property, but it is an absolute aperture property of the lens once equal FOV is established. Aside from COC, DOF is a lens property, not a format property. Quote:
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#12 |
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Join Date: Feb 2006
Posts: 17
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I really appreciate all the help you guys TCav, Bill, Greg and Brian gave. Bill, I checked out the circle of confusion and just as it stated, it confused me. lol I will not give up though and will study the formulas when I get more time. Brian, my camera goes from 2.8 to 3.7 so I will put it on a tripod (I almost always do) and use the telephoto at the max 432 mm which should default to 3.7 and see if that gets me some blury background. Thanks again to everyone and even though you don't know me, I have read so many of all of your previous posts in this site, I feel like I know all of you.
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#13 |
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Join Date: Oct 2003
Location: Indian Rocks Beach, FL
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A telephoto lenses gives the impression of a shallower DOF because it compresses the background. But the actual DOF isn't really a function of focal length.
In Bob's case he wants some foliage 3 inches behind a flower to be blurred so the flower stands out. He finds that shooting macro at 35mm (eq) doesn't sufficiently blur the background. Stuff 1 foot away will be blurred, but not the close foliage. Framing the flower the same standing back and using 432mm isn't going to make the close foliage blur any more. With the higher f stop he might have a greater rather than lesser DOF. But the stuff that is blurred a foot away will appear to be only a couple of inches from the flower because of telephoto compression, giving the impression of a shallower DOF. But the foliage 3 inches from the flower will still be as sharp because he hasn't significantly altered his DOF. This is a quote and chart from a good article on DOF: "Note that I did not mention focal length as influencing depth of field. Even though telephoto lenses appear to create a much shallower depth of field, this is mainly because they are often used to make the subject appear bigger when one is unable to get closer. If the subject occupies the same fraction of the viewfinder (constant magnification) for both a wide angle and a telephoto lens, the total depth of field is virtually* constant with focal length! This would of course require you to either get much closer with a wide angle lens or much further with a telephoto lens, as demonstrated in the following depth of field chart:" http://www.cambridgeincolour.com/tut...h-of-field.htm You will notice that even a 10mm has less than 20% more DOF than a 400mm, and the DOF is constant from 50mm to 400mm. So it is reasonable to think Bob might actually increase his DOF a little going to telephoto with a higher f stop. |
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#14 |
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Join Date: Feb 2006
Posts: 17
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Thanks Slipe, while playing around in the Cambridge tutorials you suggested, I decided to google kodak p850 macro and got this little trick which I can't wait to try out tomorrow (it is raining here now).
http://video.google.com/videoplay?do...70879980855669 There is even a short video showing the trick of how to get closer to the subject than the auto focus wants to allow. Don't know if it would work on other cameras but apparently it does on the P850. Anyway, I will try tomorrow to see if it works. Again, thanks everyone. |
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#15 | |
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Join Date: Jun 2002
Location: Hay River Township, WI
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Slipe's reference makes a good point, though it is worth seeing the footnote:
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#16 | |
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Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
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BillDrew wrote:
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#17 | ||
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Join Date: Aug 2004
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TCav wrote:
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I have both a Canon 20d (APS C sensor) and 1d (aps H sensor). If I use a 100mm lens on both cameras, same aperture, same distance to subject they produce two different depths of field. At the same DISTANCE, the smaller sensor has shallower DOF. However, for the same Field of View (i.e. adjusting distance to subject so subject is same size in the frame) the larger senser has shallower DOF. However, this isn't a whole lot of help to the OP. The OP isn't going to change their sensor size. They have control over aperture, distance (until you get to minimum focus distance) and focal length. My suggestion to the OP is this - start at the minimumum focus distance for the camera. Open up the aperture to it's widest value and zoom until your subject fills the frame. Take the shot. If you still have zoom left, back up a bit and zoom further and take a shot. Repeat until you're at full zoom. Get the photos on your computer and review the results. Don't worry about the math. Let your experience guide you. You'll quickly learn for your camera which produces the shallowest dof (closest distance/widest aperture or more zoom). Reading about circle of consusion is nice theory to understand WHY. But, for most people I think practical experience / tests drive home the practical lessons. You're not going to do calculations in the field most times anyway. |
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#18 | |
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Join Date: Jun 2002
Location: Hay River Township, WI
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TCav wrote:
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The circle of confusion is a number assigned to define what is "good enough" in terms of focus. Different people will have different ideas of what is good enough so there is no single answer. To claim the CoC depends on only one factor such as format size misses the point. John has exactly the right idea: experiment to find out what works for you with the equipment you have. I think the theory is worth figuring out to guide those experiments, and it is worth having the theory cast in the clearest possible form. Jonh's exeriment with different formats and the same lens shows the effect of magnification and distance on DoF. |
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