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Thread: Which is the Focus Distance for this scenario?

  1. #1

    Which is the Focus Distance for this scenario?

    I am planning to use the DoF Calculator http://www.cambridgeincolour.com/tut...calculator.htm

    I have a camera with f/3.5-5.6 IS specification. Sensor is 1/2.3’’ type. I am not zooming at all. So, I think, I will get f/stop as f/3.5. (Please confirm whether it is true)

    There 10 pet bottles kept in a row at a distance of 1 meter each. I am 3 meters away from the first pet bottle.

    For doing calculation, I can get the focal length after taking a sample photo and reading EXIF data. (Please confirm whether it is true)

    1. What should be the “focus distance” value to be entered here for DoF calculation?
    2. What should be the other set up to do if I want to get the fourth pet bottle only in focus?
    Last edited by Lijo; 3rd June 2013 at 08:28 AM.

  2. #2
    dje's Avatar
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    Re: Which is the Focus Distance for this scenario?

    Quote Originally Posted by Lijo View Post
    I am planning to use the DoF Calculator http://www.cambridgeincolour.com/tut...calculator.htm

    I have a camera with f/3.1-5.6 IS specification. Sensor is 1/2.3’’ type. I am not zooming at all. So, I think, I will get f/stop as f/3.1. (Please confirm whether it is true)

    There 10 pet bottles kept in a row at a distance of 1 meter each. I am 3 meters away from the first pet bottle.

    For doing calculation, I can get the focal length after taking a sample photo and reading EXIF data. (Please confirm whether it is true)

    1. What should be the “focus distance” value to be entered here for DoF calculation?
    2. What should be the other set up to do if I want to get the fourth pet bottle only in focus?
    If the camera is the SX160 you referred to in another thread, the max aperture range is f/3.5 to f/5.9 over a focal length range of 5mm to 80mm. If you are not zooming in at all, the focal length will be 5mm and the maximum aperture you can set is f/3.5. If you are fully zoomed in, the focal length will be 80mm and the maximum aperture you can set is f/5.9.

    The focus distance is the distance between the focal plane of the camera and the object you want to be in sharpest focus. For the first bottle, it will be 3m and for the fourth bottle it will be 6m.

    For this type of camera, the only way to know the exact focal length used is to look at the EXIF (unless you are at one end of the zoom range or the other when you know it will be 5mm or 80mm).

    Dave

  3. #3

    Re: Which is the Focus Distance for this scenario?

    Quote Originally Posted by dje View Post
    For the first bottle, it will be 3m and for the fourth bottle it will be 6m.
    I want clear focus on the fourth bottle and other bottles to be blurred. When I put the following value into calculator, I get infinity as DoF.

    Sensor = 1/2.3’’
    F/Stop = 4
    Lens Focal Length = 5mm
    Focus Distance = 6m

    What does infinity mean here? Can't we take a focused photo with this set up?
    How can I get a DoF with less than 10cm? What should be the set up that I need to make?

  4. #4
    arith's Avatar
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    Re: Which is the Focus Distance for this scenario?

    I think you have to be within half a metre of the subject to get 4/3 metres dof and so unfortunately it is impossible unless you can increase the focal length.

  5. #5
    dje's Avatar
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    Re: Which is the Focus Distance for this scenario?

    Quote Originally Posted by Lijo View Post
    I want clear focus on the fourth bottle and other bottles to be blurred. When I put the following value into calculator, I get infinity as DoF.

    Sensor = 1/2.3’’
    F/Stop = 4
    Lens Focal Length = 5mm
    Focus Distance = 6m

    What does infinity mean here? Can't we take a focused photo with this set up?
    How can I get a DoF with less than 10cm? What should be the set up that I need to make?
    If you put those figures in the calculator, you get the following results

    Nearest Acceptable Sharpness: 0.93m
    Furthest Acceptable Sharpness: Inf
    Total Depth of Field: Inf

    This means that even though the sharpest focus is on the fourth bottle, anything between 0.93m from the camera and infinity will be acceptably sharp. With a small sensor like this, you have no chance of getting anything like 10cm DOF at a distance of 6m.

    All I can suggest is you try some different numbers in the calculator eg for a full frame camera with a focal length of say 100mm, f/1.2. This should give you a feel for how the DOF works out for various situations.

    Dave

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    Re: Which is the Focus Distance for this scenario?

    Sorry mis read your question ....

    1. What should be the “focus distance” value to be entered here for DoF calculation?
    2. What should be the other set up to do if I want to get the fourth pet bottle only in focus?

    2. With your camera it is not possible even if you used full zoom, let alone the wide end. It is a situation where it needs to be done in editing

    1. You want focus from 3m to 30m so I would divide 27 by three and add the answer to the first distance .... 27/3= 9 ... 9+3 =12 which is the focus point you need to use if with the P&S camera you can adjust focus or AF is sufficiently precise to accurately focus at a subject at 12m to set up focus for you .. I doubt if it is possible in practice or any point doing with the calculator. The distances are so great . 27m is infinity for practical purposes.

    If you bring everything closer there could be an answer for you.
    With a P&S or bridge camera at wide zoom one forgets about selective focusing and one may be able to do it in editing.
    Thes shots taught me that. f/4.2 at 35mm and 280 zoom and even with 280 all the lamps are fairly sharp or sharp. Nikon 5700 bridge camera May 2004 Distances similar to your proposition I think.
    Which is the Focus Distance for this scenario?

    EDIT .... Thats a 8.9-71.2mm lens which would help me rather than the 5mm-? you are writing about.
    Last edited by jcuknz; 3rd June 2013 at 10:18 AM.

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