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Thread: AF-Focusing with MF cameras

  1. #1
    Super Duper
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    Unhappy AF-Focusing with MF cameras

    I am very interested how you guys handle the focusing with medium format cameras.
    Problem: at least on the screen the AF-point of my Hy6 is marked as an large area, it is the same with the Mamiya ZD, and I believe not much different with the phase cameras.
    Now I want to focus on the eye for a portrait. How do I make sure to get the eye sharp and not the nose???
    Most DSLR have much smaller focus points, and they are also marked clearly. No problem to focus on the eye with a Nikon.

    I just find it a problem to have the AF-sensors to react either on a larger area or maybe they are just not totally precise marked on the screen.

    Is manual focus or increasing the DOF the only way???

    I have shot quit some portraits which are ok but the focus is slightly in front of the eyes-what I do not like.

    Thanks for any help or suggestions.
    Tom

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    Sr. Administrator Jack's Avatar
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    Re: AF-Focusing with MF cameras

    Can't speak to Rollei or Hassy, but on my Phase body, the AF sensor area in total is pretty small -- even with all three AF points activated. So with just the center point active, it is really small, like smaller than my Canon's center AF point.

    That said, nailing a shallow DoF focus point with MF is a challenge as DoF is so narrow to begin with.

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    Jack
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    Senior Member Graham Mitchell's Avatar
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    Re: AF-Focusing with MF cameras

    AF is not perfect either. All I can suggest is manual focus and a fast lens. The 180mm f2.8, for example, is quite easy to focus manually - things really pop into focus

  4. #4
    ddk
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    Re: AF-Focusing with MF cameras

    I don't know about other cameras but on the Contax there's an AF button where your thumb sits, I'm always in manual mode but sometimes use the AF button once on the eye when I'm done focusing and it seems to work well. The upgraded Maxwell screens help a lot as a focusing aid.

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    Senior Member Graham Mitchell's Avatar
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    Re: AF-Focusing with MF cameras

    The larger focusing screen on medium format (especially WLF) is one of the main points in favour of medium format, imo, especially if you like to use a narrow DOF and very selective focus points. AF is fine for smaller sensors and smaller apertures which can catch a whole head within the DOF.

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    Re: AF-Focusing with MF cameras

    Often I position the focus point slightly to the outside of the eye and that gives me reliable eye focus on the H2/100mm and P1/120mm and P1/150mm(2.8) that I use for portraits. I'm almost always shooting tethered for portraits and I dedicate the second monitor (which I turn vertical) to a 100% focus check so that if I'm ever nervous about whether I'm nailing focus (usually when I'm shooting wide open) I just glance over at the monitor.

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    Re: AF-Focusing with MF cameras

    I wonder how big the AF-sensor-area really is with the Hy6. I will try to get more info and also to just run some tests.
    I have to say when I manually focus my 110/2.0 I allways believe to have hit focus, but when I look at the images later on many are just a little off.

    I can not understand how one should be able to manually focus a slowish zoom lens (with a dark viewfinder) precisly.

    I made the experience some time ago with the DMR and now again with the Hy6: When I use manual focus I often just dont hit the focus 100%.

    One more (maybe stupid) question: if I use a longer focal length to shoot the same subject and framing compared to a shorter focal length - would the DOF be the same? (I think not but I am not sure)
    I mean would it be easier to shoot head&shoulders with 180mm and to have nose and eyes in focus compared to do the same (from half distance) with 80mm lens?

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    Sr. Administrator Jack's Avatar
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    Re: AF-Focusing with MF cameras

    Quote Originally Posted by t_streng View Post
    I wonder how big the AF-sensor-area really is with the Hy6. I will try to get more info and also to just run some tests.
    I have to say when I manually focus my 110/2.0 I allways believe to have hit focus, but when I look at the images later on many are just a little off.
    Maybe your focus screen is not precisely calibrated to the back --- IOW maybe your back needs to be shimmed to perform properly on your specific body?

    I can not understand how one should be able to manually focus a slowish zoom lens (with a dark viewfinder) precisly.
    Nor do I However, a good loupe of auxiliary finder may help.

    I made the experience some time ago with the DMR and now again with the Hy6: When I use manual focus I often just dont hit the focus 100%.
    IME you need first perfect alignment of your focus screen and sensor position or it is futile. Next you need to make sure your diopter is perfectly set per your vision. Only when those two criteria are met will manual focus at the screen agree with the lens on the sensor -- anything else is akin to guessing.

    One more (maybe stupid) question: if I use a longer focal length to shoot the same subject and framing compared to a shorter focal length - would the DOF be the same? (I think not but I am not sure)
    I mean would it be easier to shoot head&shoulders with 180mm and to have nose and eyes in focus compared to do the same (from half distance) with 80mm lens?
    This is an ongoing argument, often misunderstood and not at all a stupid question. The simple answer is DoF is directly related to subject magnification and aperture, so while lens focal length does not come into the equation directly, it does for determining subject magnification. So yes, a longer lens used from the same position and aperture as a shorter lens will generate a thinner DoF. However a shorter lens used closer -- at the point where the subject magnification is the same as with the longer lens used further away -- DoF will be identical at any given aperture.

    Cheers,
    Jack
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    Re: AF-Focusing with MF cameras

    Quote Originally Posted by Jack Flesher View Post
    IME you need first perfect alignment of your focus screen and sensor position or it is futile.

    -- IOW maybe your back needs to be shimmed to perform properly on your specific body?

    Cheers,
    If the Hy6 design comes from the Rollei (I haven't seen one), I think you'll find there are four screws holding the focus screen in place that can be adjusted to match the position of your back. Just be careful you get the right ones...

    Edit -- oops -- or were you talking about the AF Jack?
    Last edited by shakeshuck; 2nd April 2009 at 10:04. Reason: clarification

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    Super Duper
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    Re: AF-Focusing with MF cameras

    Quote Originally Posted by Jack Flesher View Post
    Maybe your focus screen is not precisely calibrated to the back --- IOW maybe your back needs to be shimmed to perform properly on your specific body?

    Thanks Jack,
    I also allready thought that I should check accurancy of back/screen allignment. Normally Sinar checks a back with sensor and eventually adds shimming if needed.
    However I havent experienced any focus problems when shooting still subjects on a tripod. I will doublecheck.
    Maybe I have to get used to work with more DOF. I still believe that the size of AF sensor or maybe the eventually unaccurate marking of AF-sensor position on the screen might be the reason for the problem.

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    Re: AF-Focusing with MF cameras

    This came from the Leica forum - and is an easy way to check focus off your computer screen:

    http://www.komar.org/faq/camera/auto-focus-test/

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