Depth of field + Focal length question.

Discussion in 'Photography Beginners' Forum' started by Innocence, Sep 17, 2006.

  1. Innocence

    Innocence TPF Noob!

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    Dear all, :lol:

    At the moment I have a point and shoot (canon A80) and I saw some fantastic photos which were just everyday shots of people, but the backgrounds were blurred!!

    From what I could figure out, it can't be done on my camera! Unless I choose "macro" and use minimum focal length and also max aperature (2.8 i think on my camera).

    Only then, can I get things in the background to be blurry.

    I then went about and did some more research!

    The depth of field is like....mmm haha sorry, I'm not experienced and don't know how to describe it. I'll try and do a picture haha.

    CAMERA->----------|----------------------|-------------------->
    ................so like..... ^this part is in focus^

    And that's the depth of field?
    haha, no idea but it seems logical to me.

    My camera can only have it 2 ways.
    CAMERA->-|-----|----------------------------------------------->
    .................^here.

    OR

    CAMERA->----------|------------------------------------------->
    ..............................^ from here.....onwards............

    Haha, gosh I hope I am at least half right!!

    Now onto my question!
    What I'm wondering is, is it possible for me (or someone, with a better camera if that is the limiting factor) to control where the dpeth of field is, and take photos of people [things]....who are say....20metres away from me, but have the background all blurry? (without using photoshop to blur it yourself)

    Thank you very much for reading!!
    Sorry!! I'm not good at explaining things!!
     
  2. chris82

    chris82 TPF Noob!

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    i think you should save up some cash and buy a new camera,even just a low priced digital camera here is a shot i took with mine i think this is the kind of pic you want to take

    [​IMG]
     
  3. Innocence

    Innocence TPF Noob!

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    haha yes! but with more blur if its possible!!

    how is it done?
    was my understanding correct?

    what type of camera/lens do I need?

    thank you for your very quick reply!! :p
     
  4. chris82

    chris82 TPF Noob!

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    well i sort pf understood your explaination,the pic i posted was shot with a basic digital camra but that was before i found the function for extreme closeups so if i took it now i would guess it would have blured the backround even more i took a lot of shots today with the new function i found and they were briliant the backround was one big blur and the object was crystal sharp but i brook my camra so i cant show you them,im guessing your camra is older so i would sugest a newer one it all depends on how much cash you want to part with
     
  5. fightheheathens

    fightheheathens TPF Noob!

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    your understanding of DOF (depth of Field) is pretty much correct. I also have the Cannon A80, though many times i can get a blurred backround to my liking.
    The thing you must know with all cameras is that as the focal point gets farther away from the camera, the DOF also gets wider. Thats just a given with all optics.
    for example. using your method, both shots below are at a focal length of f/1.4, The first is focused at .5 meters the second at 20 meters.

    CAMERA->-----I--I--------------------------------------------->

    CAMERA->----------------------------------I------------I------>


    Further more, the longer the focal length (think more zoom) the more compressed the DOF will be. The only way that i know of to get a picture of a person at 20meters and still have a very much blurred backround is to be using a large zoom lens (200mm >) that is very fast (f2.8) I hope this helps
     
  6. Innocence

    Innocence TPF Noob!

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    thank you both for your super fast replies haha this forum is amazing!

    view4mheaven - i am just wondering how to blur background without getting really close up!

    fightheheathens - thanks for your explanation. it seems that on the A80, as focal length increases (zoom out), the DOF just blows up like....exponentially.

    Sorry, 20metres may have been a big too far, but I think my problem is that I have no experience as to how quickly DOF blows out with focal length, at what aperatures.

    Is there some sort of table or some rule which can help me? :)
    (oh, and is there a way to blur the background with the A80, not shooting a very close subject? thank you~)

    Thank you again!
     
  7. Adam E

    Adam E TPF Noob!

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    a few of things that help when trying to achieve shallow (blurred) depth of field:

    1. - shoot with the iris as open as possible. to avoid over exposure, try a faster shutter, or neutral density filters.

    2. - use telephoto to your advantage. what i mean by that is stand farther back from your subject, use a tripod, and zoom in. (not going to work in every situation, but gives nice results.)

    3. - if you can, separate your subject from the background by distance. i.e. if thre are trees in the background, have the subject move farther away from them.

    hope this helps.
     
  8. Dom0803

    Dom0803 TPF Noob!

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    I understand your pain bud.. we've all been there.

    Tight angles (high zoom) is the only way for large amounts of DoF unless you got some crazy settings and/or a macro.

    SLR would be preferable, but without the large price tag you could have a bridge SLR (it's not an SLR but SLR style camera)

    I recommend to you the Finepix S5000

    Take a look at some of my photos.. search my posts
     
  9. Adam E

    Adam E TPF Noob!

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    my girlfriend had a fuji s5200, and it was a cool camera! the ability to shoot raw was a nice plus. the one thing i didnt care too too much for was the manual focus control. its not that its bad, just different than what im used to. (controlled by buttons, rather than a focus ring.)
     
  10. Innocence

    Innocence TPF Noob!

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    ok! Thank you!

    I will go and try it now haha~
     
  11. Innocence

    Innocence TPF Noob!

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    I just went to try it!

    On no zoom, I can use /f 2.8, but if I zoom in (max is 3x) then the max aperature I can use is /f 4.9!

    Why?
    Did canon make it like this on purpose? or is there some sort of optics limitation? Any way I can change it?

    Thanks a lot!
     
  12. fightheheathens

    fightheheathens TPF Noob!

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    the F stop number = focal length divided by the aperature diameter
    so if you incrase the focal length (something that happens when you zoom in) and keep the aperature the same value, the F stop value becomes larger.
     

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