Sharp focusing with cheap (slow) lenses

Discussion in 'Digital SLR' started by David Geesaman, Oct 4, 2005.

  1. Well, here's the deal. I have a 75-300 Tamron on a 300D. Typically I
    shoot equestrian events, taking available light shots continously as the
    rider goes about. Many of these are out of focus, using either center-point
    or array focus.

    I'd like your tips on maximizing my success rate using this gear. Last
    time I tried to hit the shutter the moment I heard the focusing stop.
    Stopping down for a large DOF is a good strategy, but that can't be done
    when the light is low. For those of you (most, I'm sure) using better
    equipment, try to remember when your gear wasn't so sharp and quick.

    Dave
     
    David Geesaman, Oct 4, 2005
    #1
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  2. Turn off your autofocus and learn how to focus manually, you will catch many
    many more shots this way. Try prefocusing too and wait till the subject
    enters the zone of focus, this works well with wide open aperture shots as
    it pushes the background out of focus.
     
    Nigel Cummings, Oct 4, 2005
    #2
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  3. I've attempted the manual focusing, but my right eye (the viewfinder eye) is
    nearsighted. I guess I haven't given manual focus the old college try yet,
    but I fear I can't see well enough even with the diopter adjusted. There
    are a lot of autofocused pics that looked great thru the viewfinder but were
    crap in the end. I think I'll head out for a couple practice sessions and
    try it.

    As for the prefocusing, I've used that as well but it limits me to catching
    a much smaller number of shots.

    Dave
     
    David Geesaman, Oct 4, 2005
    #3
  4. David Geesaman

    Tony Polson Guest


    Buy a correction lens (a "diopter") for the viewfinder eyepiece.
     
    Tony Polson, Oct 4, 2005
    #4
  5. David Geesaman

    DoN. Nichols Guest

    I don't know your camera, but the Nikon D70 has a slider beside
    the eyepiece with adjusts the focus. If your camera can display
    something on the focusing screen (indicators of autofocus zone, or a
    grid, or something else which is *not* a part of the image being
    focused), use that adjustment to make the "something" as sharp as
    possible. That will increase the chances that the image when manually
    focused through the screen will be sharp.

    If there is no eyepiece focus adjustment on the camera, or if it
    does not have enough range to correct for your nearsightedness, you can
    get screw-in eyepieces made for different corrections, to make your view
    through the finder the optimum -- for you -- and increase your chances.
    So -- the camera does have such an adjustment. Remember to
    focus it on artifacts of the viewfinder such as I suggested above, and
    ideally, to leave these turned on while shooting. That will anchor your
    eye's focus point, and reduce the chances of an out-of-focus image on
    the screen pulling the focus point of your eye.
    It may be that the out-of-focus image was pulling the focus of
    your eye. Having indicators on the screen turned on can act as anchors
    for your eye's focus and help to reduce the problems.
    I understand. The things you most want to photograph take place
    somewhere other than where you are pre-focused.

    BTW -- a faster lens (larger maximum aperture) will typically
    have better autofocus behavior -- both faster and sharper -- but it
    would increase your out-of-pocket expenses.

    Good Luck,
    DoN.
     
    DoN. Nichols, Oct 4, 2005
    #5
  6. David Geesaman

    Pete D Guest

    Dave,

    If you are "loosing" that many shots anyway then why not just concentrate on
    getting a few spot on, pick your place and prefocus, by limiting the number
    of shots you take you will not be so rushed and can put everything into
    getting the few right.
     
    Pete D, Oct 4, 2005
    #6
  7. David Geesaman

    no_name Guest

    Does this lens have hyper-focal marks?

    If so, use manual focus, stop down and set it to the hyperfocal distance
    for the f-stop you're using.
     
    no_name, Oct 5, 2005
    #7
  8. I would be surprised if an image on an SLR focussing screen could entice
    your eye to focus in error.

    This is a common problem with microscopes, telescopes etc where you are
    trying to focus an aerial image - i.e. one that only exists hanging in
    space, as it were. In these cases, where you need the image to be sharp
    in a specific plane, if it is out of focus at that plane, but in focus
    at another one, then the automatic mechanism in your eye (you auto-focus
    mechanism, if you like) will often delude you into thinking successful
    focus is achieved when it is really some way out.

    The solution in these cases is to place a cross-hair or similar fiducial
    mark in the plane where sharp focus is required. If you ensure that you
    keep this sharp at the same time as focussing the image, then the latter
    will necessarily be in the same plane as the fiducial mark, and hence
    everything should be hunky-dory.

    However, this cannot (AIUI) apply to an image which is projected on to a
    ground glass screen. Your eye is constrained to examine this image, and
    cannot see a sharp aerial image at some other distance. That is, as I
    have always thought, the main point of ground glass screens. If I am in
    error here, I would certainly be very interested to see some good
    reports of how the eye's focus can be "pulled" in this way, and ignore
    the screen image, as you suggest.

    The irony is, of course, that determining a really precise focus point
    on a ground glass screen is much harder than on an aerial image, which
    is why photomicrographers and astronomers will always use that technique
    if they can. Superior SLR bodies can of course have such a screen fitted
    (for Canon 1-series bodies it is the I - capital i - screen).

    David
     
    David Littlewood, Oct 5, 2005
    #8
  9. Dave, have you tried contact lenses? I have been short sighted for all
    my adult life, and wearing spectacles I would find focussing a real
    trial. Wearing contact lenses - which I have done every day since the
    age of about 19 - I have no problems at all. (Well, apart from the
    really crap focus screens on most current AF SLRs, but that's another
    issue.)

    David
     
    David Littlewood, Oct 5, 2005
    #9
  10. I will, as soon as I find money for surgery for the dog, an engagement
    ring, (money for the wedding), and get my sports car running well again.

    Dave
     
    David Geesaman, Oct 5, 2005
    #10
  11. How would stopping down to get a larger DOF affect your autofocus? Your
    autofocus on the 300D is done at maximum apeture. It may affect the
    final image, but not the autofocus.

    I suspect that your images are not out of focus anyway, but rather you
    have lens blur from moving the camera, either because you handhold or
    track your subject. What is the speed of that lens? f/4.5 to f/5.6?
    Try choosing a faster shutter speed (will lose DOF though).
     
    Thomas T. Veldhouse, Oct 5, 2005
    #11
  12. David Geesaman

    Jer Guest


    If you're talking about that '64 Austin Healey I had, forget it. Never
    happen. :)
     
    Jer, Oct 5, 2005
    #12
  13. Quite simply - if the timing of the autofocus is off, or the subject has
    changed distance since the autofocus was last adjusted, there is much
    greater room for no visible focus error. Naturally, my concern about
    Autofocusing comes from the final image.
    This is not the case. I have many problem images shooting at 1/1000 to
    1/4000s. When the light is of concern, I go no slower than 1/320s. This is
    the reason why I have trouble with the automagic Sports Mode - it will drop
    below 1/250s without warning - and this is unacceptable.
    Also, I can usually find the depth in the picture that is in sharp
    focus.

    Dave
     
    David Geesaman, Oct 5, 2005
    #13
  14. I looked up the technique you're talking about, but I don't think it's
    marked in this manner. It's this lens here: http://tinyurl.com/76fxz.
    Thanks for the suggestion - it sounds like something I should consider in
    any future lens purchase.

    Dave
     
    David Geesaman, Oct 5, 2005
    #14
  15. I readjusted the diopter last night, and by focusing on the viewfinder's
    autofocus point markings, I think I have it set pretty accurately. I think
    in the past I was looking at the image, or being too casual about it.

    AFAIK the 300D has no markings designed to aid in manual focusing. I'll
    go back and check what the manual says about manual focusing, but I had the
    chance to eye through a 1DmkII last week and it's not set up with that kind
    of textured focus plane.

    Dave
     
    David Geesaman, Oct 5, 2005
    #15
  16. Well it is a 3rd gen RX-7, known for being a formidable challenge at
    times...

    Dave
     
    David Geesaman, Oct 5, 2005
    #16
  17. I do this for events like jumping, where the peak of action is obvious.
    When photographing dressage, the action is much more subtle, and the best
    shots come from things like the expression of the horse and rider, position
    of the horse's feet mid-gait, etc. Foot position is especially important,
    and looks best for only a split second. I theory it can be caught with
    timing, but in my practice I'm still a long way from doing it well. Since
    my camera doesn't do 8.5fps, it becomes a crapshoot and just taking many
    pictures has yielded the most pics with good composition. The problem is
    then losing so many to poor focus.

    Dave
     
    David Geesaman, Oct 5, 2005
    #17
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