Telephoto lenses and DOF at large apertures

Discussion in 'Nature' started by Phocal, Sep 18, 2015.

  1. Phocal

    Phocal Mu-43 Hall of Famer

    Jan 3, 2014
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    Last edited: Jul 28, 2017
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  2. Lcrunyon

    Lcrunyon Mu-43 All-Pro Subscribing Member

    Jun 4, 2014
    Maryland
    Loren
    Depth of field characteristics is always something I have to get used to with a new lens. The first time I took my 40-150 f/2.8 Pro to shoot butterflies, I didn't stop down enough and a part of the wings were always out of focus. Comparing it to the 75-300, the 40-150 allowed me to get very close to the butterflies, and of course it was much wider open at f/2.8.
     
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  3. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    There may be something else involved as well.

    It sounds as if you're using manual focus since you talk about shooting in a burst, refocussing, then shooting in a burst again. If you're manually focussing, there's always the chance that you are moving slightly between when you achieve manual focus and when you press the shutter. If your focus is just a little bit off and you move just a little bit as well, then you may actually be increasing the amount you're focus is off. Say your focus is .5" in front of the eye and you move back .5", in total those 2 factors move your focus to 1.0" in front of the eye. There's more DOF behind the point of focus than in front so that may not be an issue but if we change those errors to a focus point 0.5" behind the eye and a movement of 0.5" forward, the point of focus then moves to 1.0" behind the eye and there's less DOF in front of the point of focus.

    Yes, DOF is shallow but a small error in focus can easily be made worse by a small movement as well between focus and pressing the shutter. The error can also be reduced if the focus is in front of the eye and you move forward, or the focus is behind the eye and you move back but whether or not the error will actually reduce or get larger depends on the size of the error at each end and whether they work to compound each other or compensate for each other.

    My point is that you need to consider what's happening at the camera in terms of movement as well as what's happening in relation to your point of focus and the bird.
     
  4. Phocal

    Phocal Mu-43 Hall of Famer

    Jan 3, 2014
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    Last edited: Jul 28, 2017
  5. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    ^ I'm not trying to criticise your technique, merely pointing out an issue and I didn't say that it actually was part of your problem, I said it could be because I had no idea whether it was part of your problem. Part of the reason for that, rereading your original post, is that I read the text in your 2 paragraphs and looked at the images but I didn't bother reading the caption above each photo so I didn't see that the first one used a tripod while the second was handheld. I'm finding the longer I've been retired and the further I get from having to read lots of stuff where I needed to make sure that I didn't miss the fine detail, the more likely I am becoming to skim somewhere and miss an important point.
     
  6. janneman

    janneman Mu-43 Veteran

    432
    Dec 6, 2012
    Netherlands
    Jan (John) Kusters
    The razor thin DoF with longer tele is one of the reasons I don't feel the need for a very fast tele. I am quite happy with the 75-300, and the long end I prefer f8 to get a bit more DoF. The price I pay is more noise from higher iso, which bothers me less than hair or feathers slightly unsharp.