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Zone Focus/ Depth of Field

Discussion in 'Olympus Forum' started by iansurita, Apr 3, 2013.

  1. iansurita

    iansurita New to SC

    5
    Mar 26, 2013
    Kent UK
    Ian Surita
    Having used 35mm for most of my photography I never had any problem with DOF and judging acceptable focus area as all manual focus lenses had scales marked. Then moving to digital 3-4 years ago and now trying 4/3s I find this a problem as there aren't any marks on lenses. I still use my Nikon MF lenses at times and now want to do some street photography with them, so will the scales still apply accurately as they did with FF or will I have factor in some difference.

    I did a little exercise comparing my 24mm manual focus lens (giving me effectively 48mm on 4/3s) and standard 4/3s kit lens set at 24mm and focusing on the same spot. The area in focus appeared the same in each case. So can I accept this as proof.
     
  2. Hikari

    Hikari SC Veteran

    292
    Jan 5, 2013
    Maine, USA
    On m4/3, your DoF scales are off by two stops. For example, if you have your aperture set to f/11, you would want to use the f/5.6 DoF scales. Naturally, you have no scales for the two largest apertures.
     
  3. Chris2500dk

    Chris2500dk SC Top Veteran

    598
    Dec 22, 2011
    Copenhagen, Denmark
    The other way around isn't it? If you set your lens to F5.6 with a m43 sensor it will have the same depth of field as a fullframe at F11.
     
  4. bartjeej

    bartjeej SC Hall of Famer

    Nov 12, 2010
    bart
    Chris: Hikari and iansurita are talking about using an FF lens on m43. Because m43 has a 2x crop factor, the effective focal length will be twice as long as on full frame, and that longer effective focal length gives shallower DOF. So if you use the FF lens' DOF markings, as Hikari said, you'll need to use 2 stops lower than your actual aperture in order to correctly calculate DOF.

    What you're talking about is using the same effective focal length, which would compare a 12mm m43 body/lens combo with a 24mm FF body/lens combo. In that case, as you said, the DOF would be the same if the m43's lens is 2 stops faster than the FF lens - but as I said already, the question was about using both lenses on a m43 body.

    iansurita: a 24mm lens is a 24mm lens, regardless of the mount (Nikon FF or m43 or Leica M or ...), so if you use both lenses on your m43 body, they should give the same results (if you use the same aperture and focus distance, obviously).
     
  5. pdh

    pdh SC Legend

    Jan 2, 2011
    To be more precise, there is no such thing as "effective focal length" - the focal length of the lens does not change with the change of film or sensor size.

    What changes is the angle of view (the angle of view of a lens designed for a 35mm camera is halved on the m4/3 sensor as if it were twice the focal length), and the corollary of the smaller sensor is a smaller circle of confusion, which is what increases the depth of field.

    dofmaster.com has a lot of useful resources for calculating depth of field (and creating dof tables) for almost every combination of aperture, focal length and sensor/film size
     
  6. bartjeej

    bartjeej SC Hall of Famer

    Nov 12, 2010
    bart
    I'm pretty sure the smaller circle of confusion leads to decreased DOF, not increased (because 2 light rays coming from an out-of-focus point and passing through opposite sides of the lens, will have the same distance between them when they reach the sensor regardless of whether the sensor is FF or m4/3 size; however, on the smaller m4/3 sensor, that distance logically occupies a larger percentage of the sensor, so if you view both images at the same size, the point from which the 2 light rays were emitted will appear more blurred on the m4/3 photo).

    dofmaster doesn't seem to take this into account though; I compared a FF 50/2 at 3 metres with a m4/3 25/1 at 3 metres, and dofmaster gave exactly identical DOF and hyperfocal distance, suggesting only physical aperture size, field of view and focus distance are important. I'm not entirely sure I trust dofmaster though... because the CoC logic is pretty strong, if you ask me. [EDIT] nevermind, I just realized the CoC thing is basically another way of explaining the FoV's effect on DOF! So dofmaster would appear to be correct after all...

    You're right about equivalent field of view being a better term than equivalent focal length (you might've noticed me using it already:wink:)
     
  7. Ray Sachs

    Ray Sachs SC Legend

    Sep 21, 2010
    Not too far from Philly
    you should be able to figure it out...
    All of which proves rather conclusively that the circle of confusion was very aptly named.

    Just get to know your lens and you'll figure out quickly enough where the zone focus sweet spots are for different lighting conditions....

    -Ray
     
  8. iansurita

    iansurita New to SC

    5
    Mar 26, 2013
    Kent UK
    Ian Surita
    My thanks to all for the useful information, it's a great help.

    Ian
     
  9. Hikari

    Hikari SC Veteran

    292
    Jan 5, 2013
    Maine, USA
    And so is focal length, as your example shows.
     
  10. Hikari

    Hikari SC Veteran

    292
    Jan 5, 2013
    Maine, USA
    And that is really the best way. Dof scales and calculations are simply trying to model the perception of an image under certain conditions. It is based on an "average viewer." But the photographer should understand how the final outcome looks in order to most effectively anticipate results. The variables in DoF, focal length, aperture, object distance, format size, and viewing distance, are useful to understand as that give you solutions to situations.
     
  11. Gary

    Gary SC All-Pro

    Aug 19, 2012
    Southern California
    Gary Ayala
    I'm a big picture type of guy and not that much into details ... So I'm wondering if the influences not accounted for in DOFmaster and the particular differences betweens DOFmaster averages and your specific lens visually significant for general photography. I can see the differences maybe affecting highly technical photography and even macro photography, but will these differences significantly have a visual effect in, say ... landscape photography?

    G
     
  12. madmaxmedia

    madmaxmedia SC Veteran

    242
    Nov 10, 2010
    Los Angeles
    I think the DOFmaster calculations are pretty good and take all the technically relevant factors into account.

    You just need to keep in mind that DOF is a relative term, in that it is estimating what is 'close enough' to be perceived as being in focus. So the type of photography, your personal subjective preferences, etc. will also factor in. For example, if I was shooting lansdscapes and most of the subject is at infinity, I would not use the hyperfocal distance for focus, even if at the focus distance infinity will generally be perceived as being in focus- I would just at infinity or near infinity.
     
  13. Hikari

    Hikari SC Veteran

    292
    Jan 5, 2013
    Maine, USA
    Actually, many people are confused about what DoF is and so will state that DoF calculators or scales are "wrong." The 100% pixel views are really messing folks up--folks are looking at the depth of the plane of focus and using that to define sharpness which is not the DoF in the image.
     
  14. Ray Sachs

    Ray Sachs SC Legend

    Sep 21, 2010
    Not too far from Philly
    you should be able to figure it out...
    I think this is exactly what's going on. The "classic" COC assumptions that DOF master still seems to use if you don't go in and mess with them seem pretty consistent with the assumptions we used in the film days. I think now that so many people (at least those who know what DOF is in the first place) tend to pixel peep images to death. And camera manufacturers want their products to pass that 100% pixel peep sharpness test and so they use really conservative DOF assumptions in most of the electronic DOF scales out there. But we don't really view photographs that way, even if some examine them that way, and the older film-based assumptions still work for me in street shooting, which is what I tend to use zone and hyperfocal techniques for the most. In focus "enough" is the measure that matters and while there are different definitions of "enough", when it comes to the way people actually view (as opposed to examine) photographs, the older, less conservative assumptions work a lot better for me...

    -Ray
     
  15. Hikari

    Hikari SC Veteran

    292
    Jan 5, 2013
    Maine, USA
    That's it in a nutshell...
     
  16. NikkiJ

    NikkiJ New to SC

    1
    Apr 9, 2013
    Depth of Field

    I have the Olympus OMD with a lovely 45mm lens. I am recently new to photography and learning hard. I am having problems getting blur when focusing on a subject ' say 2 Feet away with Blur in the background' I am an avid follower of
    Robin Wong on the internet and have noticed on his review of the 45mm street shoot, he has got wonderful blur at wide open F1.8. However - when I do this I am not achieving the blur.
    I am just starting to understand DOF, but when I see Robins work I - get frustrated because I am not achieving the same.

    If you can help me - it would be appreciated.
     
  17. Gary

    Gary SC All-Pro

    Aug 19, 2012
    Southern California
    Gary Ayala
    You probably need greater separation between foreground and background. Can you show an example?

    Gary
     
  18. madmaxmedia

    madmaxmedia SC Veteran

    242
    Nov 10, 2010
    Los Angeles
    Do you know what aperture your shots are at? If you are in Program or one of the auto modes, the camera may be choosing a higher aperture which gives your photos greater depth of field.

    Try switching to 'A' mode and picking an aperture of 1.8.

    Best thing is to post a couple of sample photos here that we can look at.