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X-Pro1: Shallow DOF and it's affect on AF - a simple DIY test and question

Discussion in 'Fuji X Forum' started by flaxseedoil1000, May 4, 2012.

  1. flaxseedoil1000

    flaxseedoil1000 SC Regular

    25
    Apr 28, 2012
    Find a target not too far away so you can easily see it's in focus. I used a heavy towel about 6' away.

    Switch to Continuous AF.

    Set Aperture to wide open.

    Listen to the lens, it's adjusting focus non-stop to compensate for your slight hand held movements.

    Now set Aperture to f/16.

    Listen to the lens, it really calms down, much less adjusting.

    Which brings a question:

    What should be the minimum shutter speed for shooting wide open?

    tia
     
  2. flaxseedoil1000

    flaxseedoil1000 SC Regular

    25
    Apr 28, 2012
    I want a mulligan on my question.

    Keep in mind I am coming from m43 so having a DOF so shallow that focusing was difficult was not an issue.

    I'm thinking that shooting a f/1.4 at distance is not the issue, shorter distances is what makes it more difficult.

    Do you ever think that you are so close to an object that you need to stop down to insure good focus?

    tia
     
  3. Luke

    Luke Super Moderator

    Nov 11, 2011
    Milwaukee, WI USA
    Luke
    Hi Tia,
    I never use continuous AF (because the camera never knows what I plan on focusing on anyways) so I can't really address that aspect of your question.

    I understand what you're asking in your follow-up question that there is more margin for error since you will have a greater depth of field and more will be in focus, but that doesn't change the fact you should still be focusing exactly where you want to regardless of how open or stopped-down your aperture is.

    It just took me awhile to learn where it was grabbing focus in relation the box (and the distance).

    At certain distances up close you understand that the focal point will be the lower left corner of the box instead of the whole box, correct? It's worth it to play around with half presses of the shutter and changing focal points and just playing around with focus in general to see how the camera works. Once you see how it does and can predict it, it won't matter if you shoot wide open or not.

    Now obviously there are still mistakes, but it's that way with every camera. Btw, I leave the distance scale on all the time to help me identify if focus is on the correct plane or not. For example, if I am focusing on something 4 feet away and the focus confirmation beeps, and the distance reads 2 feet or 8 feet, I know I'm off of it.

    Hopefully someone smarter than me can chime in with their opinions. Fee free to post some shots where you think you missed focus to help with diagnosis, too.
     
  4. Armanius

    Armanius Bring Jack back!

    Jan 11, 2011
    Houston, Texas
    Jack
    Sometimes!

    The DOF for a 35mm lens at f1.4 for a 1.5X crop sensor is 6 inches when focused at a subject 6 feet away (according to the DOF calculator on my iPhone). At 4 feet, it becomes about 2-3 inches.
     
  5. Armanius

    Armanius Bring Jack back!

    Jan 11, 2011
    Houston, Texas
    Jack
    Although this may have nothing to do with the questions, I find that C-AF in the X100 and XP1 allows for better AF lock when the subject lacks contrast. I can get AF lock on bare walls, while I can't do it with S-AF. C-AF also allows for closer AF lock. Not as close as setting the camera to macro, but closer than using S-AF. This is all using the EVF or LCD.