infinity focus

Discussion in 'Digital Photography' started by Mr.Bolshoyhuy, Apr 8, 2007.

  1. infinity focus

    whats the opinion here of it? I suppose those single-use 35mm cameras
    have infinity focus
    as there is no focusing mechanism.
    Set to it, the camera doesnt focus, thereby using less battery power.
    But is it worth it?
    Are the pics focused and properly exposed?
    I really do hate to pre-focus and hold the shutter button half-way and
    wait for the subject
    to be where I want it. Also, if using f/8, it takes longer to focus,
    thus the moment is gone
    by the time you take the pic.

    Also, center vs. multipoint focusing. Most pics taken using center
    focus are out of focus.
    Whats it used for anyway? I see no point in MF in P&S cameras as
    well. It time consuming
    and tedious.
     
    Mr.Bolshoyhuy, Apr 8, 2007
    #1
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  2. No-focus cameras have the focus set a moderate distance out. With a
    tiny enough aperture and a low enough resolution, infinity is within the
    depth of field.

    A good DSLR camera with a bright lens will eliminate focus lag. Once
    you have a fast DSLR you'll never go back to pokey point'n'shoots.
    Center focusing is what I mostly use. I aim at what I want to be in
    focus, half-press, compose, and shoot. Multi-point is no good if you're
    opening the aperture to intentionally blur an ugly background.

    I finally figured out why you'd want to meter from a single point
    off-center - races. You can set a far edge focus point so you can get a
    focus lock before you're tracking the racer.
     
    Kevin McMurtrie, Apr 8, 2007
    #2
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  3. Mr.Bolshoyhuy

    Bucky Guest

    can't you just use set focus, aperture, and shutter in manual mode?
     
    Bucky, Apr 8, 2007
    #3
  4. Mr.Bolshoyhuy

    Neil Ellwood Guest

    He can't. He has to learn how to.
     
    Neil Ellwood, Apr 8, 2007
    #4
  5. It's particularly useful if you're photographing scenery through a window,
    to ensure that the camera doesn't mistakenly try to focus on reflections in
    the window.
     
    Andrew Koenig, Apr 8, 2007
    #5
  6. funny. I was referring to P&S cameras.
     
    Mr.Bolshoyhuy, Apr 8, 2007
    #6
  7. Mr.Bolshoyhuy

    Bill Funk Guest

    Owning a P&S camera does not automatically limit the user to no
    control.
    But, to answer your question, these cameras aren't limited or set to
    "infinity". The aperture and focus are set such that infinity is
    included in the DOF. How close the focus will go to is up to the
    designers.

    --
    THIS IS A SIG LINE; NOT TO BE TAKEN SERIOUSLY!
    The White House gave John Kerry's
    campaign nemesis Sam Fox, who funded
    the Swift Boat Veterans, a recess
    appointment to Belgium on Wednesday.
    Nothing ever changes. John Kerry
    insisted he was for the appointment
    before he was against the appointment.
     
    Bill Funk, Apr 9, 2007
    #7
  8. Mr.Bolshoyhuy

    Allen Guest

    Kevin McMurtrie wrote:

    Many years ago there was a term for the point at which a set focus would
    yield an acceptable sharpness for an object at "infinity" and also
    provide that same acceptable sharpness (circle of confusion) at the
    nearest point, for any given focal-length/f-stop combination. I have
    wracked my brain trying to remember that term, with no success; does
    anyone recall it? It _might_ have been "Hyperfocal distance".
    Allen
     
    Allen, Apr 9, 2007
    #8
  9. Allen wrote:
    []
    Correct.

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

    They give an example of focussing a 50mm lens working at f/16 to 5.2m,
    when everything from 2.6m to infinity is then "in focus".

    David
     
    David J Taylor, Apr 9, 2007
    #9
  10. Mr.Bolshoyhuy

    ASAAR Guest

    That's probably a useful definition for 4"x6" snapshooters, but
    maybe not so good for others that occasionally make larger prints.
    Maybe a better way to put it with that example would be that for a
    specific print size, focus would be best at 5.2m, but at infinity
    and 2.6m, sharpness would still be pretty good, but noticeably
    inferior with closer than normal examination, or not very sharp in
    larger size prints. For larger print sizes where a "smaller circle
    of confusion" would be needed, the hyperfocal distance would move
    slightly closer to infinity from 5.2m, and the DOF would also
    decrease slightly with the "near" DOF border moving slightly closer
    to infinity from 2.6m (by 1/2 the change in the h.d.) and the "far"
    border remaining at infinity. And of course if you give pictures to
    one of our professed pixel peepers whose places his proboscis
    against the prints for perusal, all bets are off. :)
     
    ASAAR, Apr 9, 2007
    #10
  11. Mr.Bolshoyhuy

    Paul J Gans Guest

    I suspect "hyperfocal distance" is the term.

    It is the distance such that at a given f stop with a given
    lens anything from the hyperfocal distance to infinity was
    in "focus".

    This, of course, depends on the acceptable sharpness of the circle
    of confusion. In other words folks milage may vary. The hyperfocal
    distance is fairly close by for wide angle lenses.

    Back in the Good Old Days (tm) when lenses had distance scales
    on the barrels and f stop range marks opposite them, you could set
    infinity at one range mark and read the hyperfocal distance off
    the other range mark. It was a great setting for grab shots.

    That was then. This is now.
     
    Paul J Gans, Apr 9, 2007
    #11
  12. Indeed, yes! I wrote "in focus" (with quotes), not 'in focus', to cover
    the very situation you mentioned. I wonder if with digital, because of
    the finite pixel size, the variation of focus might be less noticeable?
    It might be useful to update the wikipedia entry to cover digital
    photography as well as film photography. However, I have seen lots of
    people here get very confused over this whole issue, so that's not a task
    I'm prepared to take on!

    What's the approximate number of pixels implied by CoC 0.03 with a 35mm
    format? Would it be 36/0.03 x 24/0.03 pixels - i.e. 1200 x 800 pixels?
    Today that probably does fit into the 6 x 4 inch category!

    Cheers,
    David
     
    David J Taylor, Apr 9, 2007
    #12
  13. Mr.Bolshoyhuy

    Allen Guest

    Thanks! Just before I hit "send" Hyperfocal distance entered my
    thoughts, but I wasn't sure. It was probably 45 or 50 years ago that I
    last heard or read the term. The arrival of the SLR and then autofocus
    pretty much eliminated much of the discussion of such issues.
    Allen
     
    Allen, Apr 9, 2007
    #13
  14. Mr.Bolshoyhuy

    Scott W Guest

    You can still get lenses like that but they tend to be primes. My
    28mm f/2.8 has those markings and I make a fair bit of use of them.
    However I find they are a bit optimistic about what is in focus, so I
    use the markings that are about 1 stop wider then what I am shooting
    at. As an example if I am shooting at f/11 I would use the marks for f/
    8.

    Scott
     
    Scott W, Apr 9, 2007
    #14
  15. Mr.Bolshoyhuy

    ASAAR Guest

    I don't think so. For the pixel size to matter the sensor's
    resolution would have to be so low, or the magnification so high
    that you'd be able to see individual pixels in a print. Somewhat
    like not being able to easily distinguish between in-focus and
    slightly out-of-focus parts of a high quality glossy magazine
    picture because you're using a loupe to examine half-tone dots. If
    the pixels aren't large enough to see, by definition they're already
    smaller than the CoC size which is small enough so that the eye
    can't easily distinguish between the most in-focus and most
    out-of-focus objects within the DOF.

    That represents quite a small crop from a FF sensor, slightly less
    than 1mp. With 12.8mp, the 5D has about 13x the number of pixels,
    and 13x the 6 x 4 size == 13 * 24, or 312 square inches for a
    comparably sharp picture using the entire sensor. That's about 50%
    larger than a 12" x 18" print. DPReview's glossary entry for Circle
    of Confusion comes up with a CoC size of 0.033mm, virtually the same
    as your 0.03mm.


    http://www.dpreview.com/learn/?/Glossary/Optical/Circle_of_Confusion_01.htm


    After a recent flurry of messages trying to see if the number of
    shutter actuations was contained in EXIF data, I downloaded Exiftool
    and applied it to some of my Fuji S5100's images. It shows
    considerably more information, but not the number of shutter
    actuations. Where Irfanview shows only "FocalLength - 8.4000 mm"
    for one particular , Exiftool shows:
    Considering the very small sensors used in P&S cameras, they've
    got some really hard working lenses. :) I don't think that in this
    case that focusing the camera at the hyperfocal distance would be a
    good idea since the camera was well focused on a niece's face which
    was probably no more than 1m from the camera. Had it been focused
    several meters behind her I'm pretty sure that her face would have
    been considerably out of focus. As it is, the small print on a can
    of Pepsi held only a couple of inches in front of her face as well
    as the wallpaper about 2 to 3 feet behind her isn't particularly
    sharp. The aperture was f/4.5, btw. Of course this is from looking
    at it on a monitor. The small print on the can might be barely
    readable if a 4"x6" print was made, but what could be seen probably
    would appear to be nicely sharp on such a small print. :)
     
    ASAAR, Apr 10, 2007
    #15
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