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Background defocus

Discussion in 'Open Discussion' started by DarrenG, Jan 16, 2011.

  1. DarrenG

    DarrenG Mu-43 Regular

    Jan 3, 2011
    Hampshire, UK
    Apologies in advance for what, I realise, is a newbie question.

    I'm trying to achieve background defocus but am confused as to how this is done. I thought it needs a large aperture but I've yet to see the result I'm trying to get.

    Can anyone explain how it's done? I'm using a GF1 with the 14-45mm kit lens.

    Be gentle!
  2. Danny_Two

    Danny_Two Mu-43 Regular

    Oct 30, 2010
    It's called Bokeh or depth of field (DoF), and you won't get a tremendous amount with that lens.
    Bright primes are the best for a shallow depth of field, get the 20mm and you'll be going bokeh mental.
  3. For a lens like the 14-45mm you need the longest focal length, the largest aperture, and a close subject. M4/3 doesn't lend itself to blurred backgrounds as much as SLR cameras with larger sensors because you are using shorter focal lengths to acheive the same framing. You really need to be looking at lenses with max apertures of around f2.8 or bigger for the best effect.
  4. pdh

    pdh Mu-43 Top Veteran

    May 6, 2010
    they aren't synonyms - bokeh is about the subjective impression given by the out of focus areas or highlights -- depth of field is the distance in front of and beyond the point of focus in which the image appears sharp.
  5. DarrenG

    DarrenG Mu-43 Regular

    Jan 3, 2011
    Hampshire, UK
    Thanks guys, the 20mm is on route (colleague bringing one back from the US).

    I'll experiment with that once I have it in my mits!
  6. ~tc~

    ~tc~ Mu-43 Hall of Famer

    Oct 22, 2010
    Houston, TX
    Remember that a larger f-stop number is a smaller aperture opening and a larger depth of field.

    For best subject isolation through selective focus, you want small f-stop numbers like 1.7 or 2.8
  7. deirdre

    deirdre Mu-43 Top Veteran

    Aug 9, 2010
    You can also do it in post, but the results are never quite as pleasing to me. That said, for years I did it in post when I only had slow lenses.
  8. Fiddler

    Fiddler Mu-43 Veteran

    My understanding of it is this:

    1. Have your subject as far away from the background as possible.

    2. Get yourself as close to the subject as the desired shot allows you to be.

    3. Open up the lens.

    4. Zoom in.

    5. Make sure you are accurately focussed on the subject.

    6. Shoot.

    That's what I do, anyway.

    All the best,

  9. AceStar

    AceStar Mu-43 Regular

    Jan 9, 2011
    Melbourne, Australia
    To get more background defocus on a given camera:

    a. Increase focal length (zoom in)

    - or -

    b. Widen aperture (lower f/ratio)

    - or -

    c. Get closer to your subject

    The kit zoom is particularly not very good for background defocus due to not having a particularly wide aperture, but if you zoom right in to 45mm and use the widest aperture and focus on something really close (like a flower) then you'll get it. If you're serious about this, get a fast prime lens that's on the tele side of normal. An adapted old 50mm fast prime would be good at this and inexpensive (useful for portraits).
  10. Ulfric M Douglas

    Ulfric M Douglas Mu-43 Hall of Famer

    Mar 6, 2010
    Your lens just isn't built for blurry backgrounds.
    (Actually, neither is the 20mm ... because it is 20mm)

    An ideal lens would be a 50mm,f2-ish : very pleasing effect.
    For cost-effectiveness you can get a cheap film-SLR version with an adapter.
  11. DarrenG

    DarrenG Mu-43 Regular

    Jan 3, 2011
    Hampshire, UK
    Thanks guys, I at least now know that my admittedly basic understanding of the technique was right.
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