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Thread: Understanding Depth of Field

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    Understanding Depth of Field

    This probably belongs in a tutorial of some sort but I think that it should have some critiquing first and I also don’t have authority to create new articles so let me know what you think.

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    Understanding Depth of Field
    Depth of field is the range of distance, in front and behind the exact plane of focus that appears acceptably sharp. Note that depth of field is our perception of acceptably sharp not what is exactly focused. Depth of field does not change abruptly from sharp to blurred but transitions gradually as the distance increases in front of and behind the focal plane.

    There are a lot of aspects that affect depth of field including: focal length of the lens, aperture setting, distance to focused object and the size of the print or viewing media. (The bigger the photo the more noticeable are the effects of depth of field.)
    Focal Length
    To achieve optimum performance, a modern photographic lens has many elements. If these elements were to be replaced with a single lens to give the same magnification, the focal length would be the distance from the centre of that single lens (focused at infinity) to the focal plane where the film or sensor is located.

    The longer the focal length the more depth of field will have an effect on the outcome.



    Distance to the Object
    If the objects of focus are at a considerable distance (like on the horizon) the depth of field is considerable. For example: a mountain in the background and a tree in the foreground some thirty metres away. Both objects would appear pretty much in focus. But say we focus on a flower only 300mm away from the camera; the effect of depth of field becomes very apparent.

    Aperture or “f stop
    Aperture is essentially the size of the hole that lets the light in through the lens and into the camera to enable the photo to be taken. The “f” number if determined by the focal length divided by the size of the opening.

    The larger the aperture (smaller “f number”) the tighter depth of field and the more blurred unfocused objects will appear. The smaller the aperture (larger “f number”) the greater depth of field and the less blurred unfocused objects will appear.

    Aperture is usually the most accessible attribute that can adjusted quick and easily to change the depth of field, however it should be noted that reducing the aperture (increasing the “f number”) will also reduce the amount of light entering the camera, therefore more time will be required to obtain the same amount of light to expose your film or sensor: increasing your “f number” will reduce your shutter speed.





    The Cooperative Dragonfly
    Macro photography is greatly affected by depth of field. Below are a number of photos taken of a dragonfly that was most cooperative as it stayed still long enough for me to take a few photos with different aperture settings. All photos are taken with a Canon 100mm macro lens.


    f=2.8, Exposure: 1/1600 sec


    f=6.3 Exposure: 1/250 sec


    f=11, Exposure: 1/80 sec


    f=32, Exposure: 1/10 sec

    Using Depth of Field to Your Advantage
    Having the background out of focus so that the object stands out can add a three dimensional aspect to the photo, so use this to your advantage. Also annoying objects in the foreground can almost be removed with good placement of the camera and use of depth of field. Say for example birds in a cage. If you push the lens right up to the cage, block most of the light that would illuminate the bars in front of the lens and select a suitable aperture size, the bars of the cage will disappear.





    Homework
    Most modern SLR cameras have a depth of field preview button which will show you what the depth of field will be like before you take the photo. Your homework is to read the manual for your particular camera find the depth of field preview button and learn how to use it well.



    Test Sheet
    Below are a number of photos taken of a test sheet that was printed and laid on the table and photographed at a steep angle to demonstrate the effects of different aperture settings on depth of field. All photos are taken with a Canon 100mm macro lens.


    Aperture: 2.8


    Aperture: 5.6


    Aperture: 11.0


    Aperture: 22.0




    If you would like try this out for yourself, a "PDF" version of the test sheet can be obtained from:
    "Future link to pdf file"

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    Maybe you could add something on the Circle of Confusion

    http://en.wikipedia.org/wiki/Circle_of_confusion

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    Nice. But I'm afraid it should be spelled "focal plane". :/
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    Arch-Σigmoid Ausphotography Regular ameerat42's Avatar
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    For a start, mate, get the spelling right. "Plain" is where the rain falls abroad. Although lenses only ideally focus in a PLANE, it is not in Spane!
    Also, in your 2nd pair of diagrams, there's no explanation for the phenomenon, ie, why a "narrower cone" should yield a greater DOF.
    Marshal the facts into a more structured dissertation.
    A(he)m.
    CC, Image editing OK.

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    are these your pictures and words ? just wondering
    Darren
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    Constructive Critique of my images always appreciated

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    Yes all the wording and the pictures are mine except the photo of the old style aperture (from Wikipedia), and yes spelling is not my best attribute.

    Circle of Confusion would be a nice thing to add to the article, though it can get quite technical and I would have to spend a bit of time drawing some diagrams to show just how it all works.

    The test sheet which you can see in the artical was constructed in AutoCAD and converted into a "pdf" file (originally set up to teach my son-in-law about depth of field). Does anyone know how we could get it stored on the net somewhere to make it downloadable?

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    cutlery so to shoot say a flower with the background blur like you have up top would one use Aperture: 2.8 or Aperture: 5.6 or something other. Also what about shutter speed would it be slow or faster
    All experts were once beginners

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    Administrator ricktas's Avatar
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    Quote Originally Posted by Nikkie View Post
    cutlery so to shoot say a flower with the background blur like you have up top would one use Aperture: 2.8 or Aperture: 5.6 or something other. Also what about shutter speed would it be slow or faster
    What did you learn from doing the aperture challenge in the New To Photography forum Nikkie? The rules do not change depending on subject, the same applies across the board when using your camera. You already know the answer to your own question here, just go back to the NTP challenge and think about it and you will be able to answer this one for yourself.
    "It is one thing to make a picture of what a person looks like, it is another thing to make a portrait of who they are" - Paul Caponigro

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    Ausphotography Site Sponsor/Advertiser OzzieTraveller's Avatar
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    G'day Cutlery

    Good first go at describing & delineating the topic
    suggestion - I have been doing this type of "technical writing" since the mid 70s - I would be happy to help you if it suits
    PM me off-line ~ I'm happy to offer you info & advice

    Regards, Phil
    Of all the stuff in a busy photographers kitbag, the ability to see photographically is the most important
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    Quote Originally Posted by ricktas View Post
    What did you learn from doing the aperture challenge in the New To Photography forum Nikkie? The rules do not change depending on subject, the same applies across the board when using your camera. You already know the answer to your own question here, just go back to the NTP challenge and think about it and you will be able to answer this one for yourself.
    slower thanks Rick and thanks for making me figure it out myself I just have a lack of confidence with myself esp when learning something new I will get there one day

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    Great post! Very informative. Now to remember it all

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    Not sure which dragonfly I like the best. Enjoyed the read as well

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    Great post and great write up. Thanks, very handy

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    Some helpful tips, thanks

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    Thanks for the tips re aperture... very helpful

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