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Thread: close-up work maximum depth of field

  1. #11

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    close-up work maximum depth of field

    Rob is right, at 1:1 magnification the 64 aperture will become effective 128 aperture! The diffraction will be as a normal 128 aperture too = awful.
    GPS

  2. #12

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    close-up work maximum depth of field

    My experience indicates that depth of field is a solely a function of image size (at the same f-stop).

    Blowing a 3" orange up to 4" will result in exactly the same depth of field, no matter what lens focal length you use.

    Three factors come to mind when chosing a lens focal length:

    First, a short lens may be required if you have a limited bellows draw. To be set up properly, many macro shots require a second set of monorail camera bellows, a third standard and extra rail extensions. Sometimes two tripods.

    Second, a longer lens is helpful to get the camera back from the subject, out of the way of the lighting equipment.

    Third is perspective, as a function of point-of-view. In the case of a sphere, for example, the farther away the lens is, the more surface area can be seen. Moving closer results in a view of much less than 180 degrees of the peel. Same thing happens to (round) faces in portraiture.

  3. #13

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    close-up work maximum depth of field

    Mr. Geiger's suggestion is something I worked with a few years ago. There was a paper (darned if I can find it at the moment) done about ten years ago by a PhD candidate that gives the method and formulas for calculating camera distance for each shot to accomodate focal length changes. It is tedious and not all subjects are particularly susceptable. Erasing differential layer parts is not quite the way to go, but it points in the right direction.

    But my guess is that your application is not high-stakes enough to warrant the time and money to pursue the infinite DOF approach. Correct? (There is, or was, a tentative product from Sweden that included the specialized focusing camera and software but it's all little digital format stuff.)

  4. #14

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    close-up work maximum depth of field

    using the Linos(Rodenstock) software I gave the link for, here's what you get for 90mm and 210mm lenses.

    www.visualperception.co.uk/lfpf

    in both cases I have set the aperture to f32 since setting it smaller causes the coc spec of 0.1mm to be broken, i.e. coc becomes larger because of diffraction( although thats probably not the correct terminology)

    note also that in both cases the effective f no is f64.

    so to answer the original question, your are correct, what you are trying to do is limited by the physics of the lenses and you will get very narrow dof, around 13mm for a coc of 0.1mm.

  5. #15

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    close-up work maximum depth of field

    I have placed this graph on a temporay web site ; when the link expires in 3 weeks, please e-mail me for a copy.



    Comparison of total depth-of-field for 3 different focal lengths of 90, 150 and 210mm
    with the same numerical aperture and same magnification ratio same circle of confusion, 100 microns


    Basically for a given magnification and same numerical aperture, classical DOF models tell us that DOF is the same better than within 10% for a 90, 150 and 210 as soon as the magnification ratio is bigger that 1/10. Or as soon as the objet is located at a distance closer than 10X the focal length.

  6. #16

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    close-up work maximum depth of field

    Some additional info
    - up to f/32 (effective f/64 at 1:1) geometrical DOF des not change by more than 10% for the 90, 150 and 210 as soon as the object is closer than 10x the focal length; and at f/45 (effective f/90 at 1:1) the 10% change in DOF is reached at 1:5 for the same set of lenses... provided that diffraction is negligible... whihc is no longer the case.
    - at 1:1 ratio no need for any software, total geometrical DOF is simply 4.N.c ( plus or minus 2 Nc) where c is the CoC (say : 100 microns) and N the numerical aperture as engraved and valid at infinity.

  7. #17

    close-up work maximum depth of field

    Well, as usual, everyone's knowledge is extremely impressive and I can't thank you enough for the concerted effort you have put into this. While I take my work EXTREMELY seriously and I expect and hope this body of photography will eventually be exhibited, my technical acumen is limited and a lot of the terminology being used is well over my head. I assume it would be worth it to me to eventually learn a bit more.

    For now, I wonder if anyone can reduce all of this great information to tell me what my best option is? My inclination again is to shoot with the 150 or the 210 so that I can maintain a distance from the subject. Is it best to assume that I should use less of the total area of the film (i.e. move further away from the subject so that it doesn't fill the frame) and shoot at f45 or f32 so that I can maximize the lens quality while also getting more depth of field?

    I apologize that I can't communicate on the level that most of you are able to and hope that it can be reduced a bit for me.

    MANY thanks.

    Sincerely yours,
    Serge

  8. #18

    close-up work maximum depth of field

    According to Leslie Stroebel's book, as I remember, you are better with a somewhat smaller image on film, and then enlarging it to whatever print size you need. Within 'reasonable' limits. Diffraction, as a factor limiting image quality, will be somewhat less this way.

  9. #19

    Join Date
    Jul 2005
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    close-up work maximum depth of field

    by installing the predesigner software I gave you a link to, you can calculate the optimum distance to give you the maximum magnification within your dof limits.

    All you need to do is to set it up with same parameters as in the following img and then adjust "object distance" and/or "stop radius" to get the maximum maginification available within your criteria.

    n.b. without knowing the actual dof required and the height of the object it is impossible for anyone to give you an accurate answer. The software allows you to calculate it exactly by palying with only two parameters. Pay attention to the infinity fno since that is what you have to set on the camera so it must be available on your lens. If coc gives a red error message then you know your into diffraction problems and will lose sharpness. You can also play with coc if you choose to.

    the following gives the lens to object distance of 630mm which provides 0.5x magnification and 54mm of dof if you set you your fno to f45



    get your ruler out and have fun.

    p.s. I would allow at least 20% margin of error if I were you, since your particular lens design plus film flatness etc etc all come into play.

  10. #20

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    close-up work maximum depth of field

    Rob, was your example just an example or were you seriously suggesting that an 0.1 circle of confusion is appropriate?

    Assuming no defocus blur, that allows separation of details no closer than 0.2 mm apart on the subject. Serge might be better off with a Pen F than with a Sinar.

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