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Old Mar 4, 2005, 8:54 AM   #1
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I have a 20D and want to get a lens with a really big aperature to be able to focus on a small object in a crowded frame and blur everything else. Anyone have any suggestions??
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Old Mar 4, 2005, 10:15 AM   #2
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Of course you want the aperture full open and it sometimes helps to have a neutral density or even polarizing filter with something like a f1.4 lens. The largest aperture lenses are usually fixed focal length, but if it is zoom you want it at the longest focal length.

That pretty much fixes your DOF to a certain range. If you need both the foreground and background blurred that is about it – max aperture and focal length.

But if you just want to blur the background you can mess with the depth of field by focusing closer to the camera than the actual subject. Fixed focal length lenses often have a scale on the lens for different apertures. You look opposite the indication to see what distance is there and then move it to the closer mark for the aperture you are using. You can see the DOF right on the marking if the lens has it.

You can do the same thing with manual focus. Focus closer until the subject slightly blurs and then move back a hair until it is sharp again. Since digital pictures are free you can shoot a few at different focus distances centered around where the image first appears sharp.

The area the markings on the camera are giving you to focus in is called the circle of confusion. While there is only one exact focus distance, there is a range where the circles generated by being out of focus are so small that it appears to still be in focus. If you focus to where this "circle of confusion" point is nearest you the background is blurred a lot more.

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Old Mar 4, 2005, 10:35 AM   #3
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Thanks...but the circle of confusion confused me a little. Are you referring to the focus points I see in the view finder? I'm sorry but I have way more camera than I need. I'm trying to catch up with it. I went off the deep end when I bought it. I just got into photography and love it but am still very ignorant. Thanks for the reply!
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Old Mar 5, 2005, 9:33 AM   #4
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There are 2 things you will need to accomplish this:

1.) A lens with a larger focal length can give less depth of field.

- I have had success with a 70-210mm.( you'll be surpised how little

depth-of-fieldyou will have

2.) A larger aperature ( smaller F-stop) gives less DOF.

If I understand what you want to do, is have a subject in a crowded frame in focus, and everythingelse blurred.

Using a lens with long focal length, and seeting your camera to "spot focusing" will help achieve this. Most cameras offer a way for you to choose the area the camera focusus on. With this technique, everything in front of and in back of your subject should be out of focus and blurry.

Hope this helps.
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Old Mar 5, 2005, 12:08 PM   #5
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This link will tell you all you want to
know about DOF and circle of confusion.

http://www.luminous-landscape.com/tu...ries/dof.shtml
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Old Mar 5, 2005, 3:42 PM   #6
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G Hayes,

Just get yourself a 50mm F1.4, or F1.8 lens, and shoot with the aperture wide open.

You will definitely blurred background.
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Old Mar 7, 2005, 7:39 AM   #7
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Thanks for the feedback...Now I have some reading and playing to do!
I just got done reading the link and must say it was helpful in understanding the circle of confusion. You all are great! I hope I don't get on too many nerves with all the dumb questions that I'll probably post to these boards!


Grady

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Old Mar 7, 2005, 10:44 AM   #8
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its called a macro lens

macrosare available in 50mm 90mm 105mm 150mm 180mm and higher

or if you want you can use extension tubes

the longer the focal length the shallower you get in DOF wide open. you also get to shoot from further away. with a 50mm macro you can climb on top of and object within 19cm f 2.8-f45 and shoot using the f stops to control the DOF whereas the 150mm has a 38cm min focus distance which allows for better lighting again with control. a tripod is highly recomended. at f2.8 the DOF is shallow.
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Old Mar 7, 2005, 8:14 PM   #9
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What do you want to take shots of???

e.g. You need a macro lens if you are taking shots of insects, flowers etc.

If you're shooting people, you may need an F1.2 50mm lens.

If you're shooting birds, animals etc, from a distance, you need a larger aperture fixed tele lens.


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Old Mar 7, 2005, 8:41 PM   #10
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This is what started it....I was sitting at the kitcken table one morning and there was stuff all over it. Just junky. I wanted to take a picture of a pack of cigarettes in the middle of all the other junk and have only the pack in good focus. Needless to say I didn't really achieve that. I got the effect in general but not to the extent that I wanted to. I had seen pictures in a photography book that I have of a chess board with a few peices on it and only one in focus so I knew it was possible but I couldn't get it.:angry: Every since then I've been playing and have gotten a little better with it but not much. Thanks again!


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