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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
    For the past year my main wildlife lens has been the Olympus 50-200 SWD with the EC-14 for the added reach. Before that I either used a Canon FD 400 ƒ4.5 or the Olympus 75-300. When using the autofocus lenses I have always just focused on the shoulder of the bird because it was much easier then trying to focus on the tiny moving head. The 50-200 with the EC-14 is ƒ4.9 when wide open and I have always seemed to get the eye in focus without any real problem.

    Well I recently got the Olympus ZD 150mm ƒ2.0 but have not taken it out for wildlife photography much. Yesterday was the first real chance I had to take it out since doing the focus tune calibration on it a few months ago. I was using the EC-14 for the most part because the birds were pretty jumpy and I could not get close enough. Anyways, I was going thru my photos and got to point where I was going to grab my little tuna and thru it out the door. Not one photo had the eye in sharp focus and I was questioning my abilities. All the photos where taken wide open at ƒ2.8. That was until I came across this photo that had the eye in focus and I noticed that I had switched to ƒ4.0 for that shot. So that got me thinking that maybe I really did need to stop down when using the TC to get sharp photos, but then I realized I never had that problem with the SWD and always shot it wide open. So I thought about my shooting technique and I realized that I typically focus on the shoulder and the SWD is ƒ4.9, maybe it has to do with the DOF. Here is the photo where I focused on the shoulder at ƒ4.0 and the eye is in focus. It is not the best photo compositionally and a terrible background with foreground stuff causing blurry areas on the sides, but it is the only one that I have at the moment to demonstrate this.

    EM1 w/ ZD 150mm + EC-14 (212mm) - 1/1600 @ƒ4.0, ISO 200 w/ tripod at Brazos Bend State Park in eastern Texas
    21338599808_4851223b24_o. ZD 150 w/EC-14 f/4.0 by Bohicat, on Flickr

    So I started thinking about the photos I took that day (I have still not gone thru all of them) and I remembered a bird I had gotten real close to so I focused on the head. I quickly found those photos, I shoot in burst and typically will shoot a burst and refocus and shoot another when the bird is stationary. Even tho I used the focus tune software and know I have the focus adjusted as best as I can, PDAF is not perfectly accurate and there is some variation in the focusing. So my doing several focus and burst helps ensure I got the shot in focus. This set of photos was shot wide-open with focus on the eye. As it turned out the eye is in perfect focus, but if you look you will see that the shoulder of the bird is out of focus (unlike the above photo where the eye and shoulder are in focus. The difference in distance between the eye and shoulder of this bird is somewhere between 1 and 2 inches. That is not a lot of distance and until today I did not realize just how small of area the DOF is at ƒ2.8 with a telephoto lens. It is times like this that I am glad I shoot µ4/3 and have a bit more DOF then full frame. Now I know that I have to focus on the eye and watch my point of focus a lot closer when shooting the little tuna wide-open even with the EC-14 attached.

    EM1 w/ ZD 150mm + EC-14 (212mm) - 1/2500 ƒ2.8, ISO 200 handheld at Brazos Bend State Park in eastern Texas
    21526070745_fda9514b93_o. ZD 150 w/EC-14 by Bohicat, on Flickr
     
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  2. Lcrunyon

    Lcrunyon Mu-43 Top Veteran

    758
    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
    I get what you saying and maybe I was not clear. A lens that uses PDAF has some error in and will not focus exactly perfect each time. It could be right on or a little forward/behind the exact point it things it is focused at. Unlike CDAF that is almost perfect each time. It's one the differences between the two types of focusing, along PDAF being much better at continuous focus. So for a stationary bird I will autofocus shoot a burst then re-autofocus and shoot another burst. When photographing one that is striking a fish I just autofocus (typically on the shoulder) and shoot, hope the error in PDAF worked in my favor. Shooting at f/4.9 has always provided enough DOF to get shoulder and eye in focus. But I have now learned that shooting at f/2.8 I have to focus on the head.

    The first photo I was shooting from the tripod so I was not moving forward or backward and any movement was from the bird. I shot 3 or 4 different burst at f/2.8 and in each the shoulder was in focus and the head was not. The one burst at f/4.0 had all photos with the shoulder and head in focus.

    The second photo I was shooting handheld and could have possibly moved forward/backward but is not likely. Each photo in probably 5 or 6 burst had the eye in focus and not the shoulder.

    I'm retired Navy and was a qualified Expert shooter (the highest of three categories) and been shooting rifles my entire life. For a year I shot my FD 400 on a Fuji XE1 (no image stabilization) mostly handheld with a better then 80% keeper rate, I have a very steady hand when it comes to shooting (rifle or camera).
     
  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

    414
    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.