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Thread: DOF & Focal Length

  1. #1
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    Default DOF & Focal Length

    Hi all,

    I'm using D90 18-55mm & 55-200mm.
    Just wondering how does focal length affects DOF?
    When using 18-55mm, i can't seems to have a shallow DOF but 55-200mm is ok.
    Set to Aperture priority.
    Anyone can advise what's my problem?

  2. #2

    Default Re: DOF & Focal Length

    With the same Aperture, longer focal length will give u a shallower dof (more background blur). that explains why u get a shallower dof with your 55-200mm.

  3. #3

    Default Re: DOF & Focal Length

    hmm... to double checking.... get a F1.8 50mm, and no need long focal length rite?
    D90|10-24mm f3.5-4.5G|70-300mm VR f/4.5-5.6G|18-105mm VR f/3.5-5.6G|35mm f/1.8|SB700|MB-D80

  4. #4

    Default Re: DOF & Focal Length

    Quote Originally Posted by desertstrike View Post
    hmm... to double checking.... get a F1.8 50mm, and no need long focal length rite?
    Yes. If you are shooting at f1.8 - f2.8, you will still get a very shallow DOF even though the focal length is only 50mm. Do take note that for most prime lens, shooting at wide open (f1.8 in this case) will result in photos that are a bit soft. If you want very sharp photos, you should normally shoot at 2-stop above the maximum aperture but that will varies from len to len.

  5. #5

    Default Re: DOF & Focal Length

    DOF is determined by 3 factors:

    1. Focal length (longer -> shallower DOF)
    2. f-stop (smaller number -> shallower DOF)
    3. Subject-lens distance (nearer -> shallower DOF)

    do check out some videos on DOF avail at You-Tube..

  6. #6
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    Default Re: DOF & Focal Length

    Hi guys,

    Thanks for the many replies.
    18-55mm has marking of 3.5-5.6 on the lens
    Does that means that the f number is 3.5-5.6?
    So the 3.5 would give the shallowest DOF?

    Also, anywhere on the web or any book I can read on DOF, focal length, aperture & shutter control?
    e.g when to use what aperture & shutter number.
    Thanks for all the many seniors here for the patience & guidance to us newbies.

  7. #7
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    Default Re: DOF & Focal Length

    18-55mm F3.5-5.6
    this means that at 18mm the largest aperture u can go is at F3.5.
    And at 55mm the largest aperture u can go is at F5.6.

    When u see something like this 17-50mm F2.8.
    This is a constant aperture lens which is more expensive because at any focal length, the largest aperture can be at F2.8.

    Here is one website that provides explaination on the photography terms:
    http://www.dpreview.com/learn/?/Glossary/ read and understand more on the exposure
    Last edited by 2ichigo2; 9th December 2008 at 05:08 PM.
    Canon 400D + 50L - Everyone was once a Noob

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    Moderator Octarine's Avatar
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    Default Re: DOF & Focal Length

    Quote Originally Posted by alv777 View Post
    Also, anywhere on the web or any book I can read on DOF, focal length, aperture & shutter control?
    e.g when to use what aperture & shutter number.
    Thanks for all the many seniors here for the patience & guidance to us newbies.
    Look, it's just right on top of all threads in Newbies Corner as a sticky one, called "Photography Notes for Newbies"

  9. #9
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    Default Re: DOF & Focal Length

    Quote Originally Posted by Octarine View Post
    Look, it's just right on top of all threads in Newbies Corner as a sticky one, called "Photography Notes for Newbies"
    Have already read it but that only gives a generally understanding of what they are but not indetail how & when to use them.

  10. #10

    Default Re: DOF & Focal Length

    Quote Originally Posted by alv777 View Post
    Have already read it but that only gives a generally understanding of what they are but not indetail how & when to use them.
    i think 2ichigo2 answer u very well already
    clear, consise and to the point
    D90|10-24mm f3.5-4.5G|70-300mm VR f/4.5-5.6G|18-105mm VR f/3.5-5.6G|35mm f/1.8|SB700|MB-D80

  11. #11

    Default Re: DOF & Focal Length

    Quote Originally Posted by alv777 View Post
    Have already read it but that only gives a generally understanding of what they are but not indetail how & when to use them.
    With countless lighting conditions and the photographer's different intentions of portrayal, it is impossible to give a generic answer on when to use what.

    It would be better if you provide a photo that didn't work out, then its easier for us to advise on the adjustments to the settings.

  12. #12
    Member Lord Soth's Avatar
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    Default Re: DOF & Focal Length

    Quote Originally Posted by alv777 View Post
    Have already read it but that only gives a generally understanding of what they are but not indetail how & when to use them.
    I suggest you try this article instead.

    http://www.mir.com.my/rb/photography...r/aperture.htm

    http://www.mir.com.my/rb/photography...mls/depth.html

    His English is not perfect but his explanation of basic camera concepts is quite clear.

    As a bonus, he uses his daughter who is quite good looking.... hee hee
    Last edited by Lord Soth; 9th December 2008 at 10:25 PM.
    | Nikon D700; AF-S 14-24 f/2.8GED; AF 20 f/2.8D; AF 50 f/1.4D; SB400| Tamron AF 28-75 f/2.8 A09NII|

  13. #13
    Moderator Octarine's Avatar
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    Default Re: DOF & Focal Length

    Quote Originally Posted by ahbian View Post
    With countless lighting conditions and the photographer's different intentions of portrayal, it is impossible to give a generic answer on when to use what.
    A good starting point is using P mode and see what the camera suggests. Knowing the basics you are able to adjust one parameter (e.g. aperture) to achieve a certain effect (DOF) - the camera will adjust the shutter speed to 'follow'. Adjust the ISO speed if necessary. Check the camera manual about how to set certain parameters and what they mean. Good idea to follow scientific approach: change only one parameter, leave the others untouched and watch the outcome.

  14. #14
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    Default Re: DOF & Focal Length

    Thank you all bros for the replies.
    Will read thru those suggested sites to learn more & shoot more photos.

  15. #15

    Default Re: DOF & Focal Length

    Try the website to get a better understanding of DoF:

    http://www.dofmaster.com/dofjs.html

    Goodluck!

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