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  1. #11

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    Thanks for the responses everyone. This is a head-on architectural shot of a building facade. So I won't be using the tilt function, just shifting to get the equivalent of front rise. So I guess the answer is I can assume the same depth of field charactersitics. Excellent news. It also makes more sense to me now why the depth of field scale is narrower on the PC lens - shorter throw. I should have thought of that before. Seems logical enough.

    Michael

  2. #12
    RalphLambrecht's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    Thanks for the responses everyone. This is a head-on architectural shot of a building facade. So I won't be using the tilt function, just shifting to get the equivalent of front rise. So I guess the answer is I can assume the same depth of field charactersitics. Excellent news. It also makes more sense to me now why the depth of field scale is narrower on the PC lens - shorter throw. I should have thought of that before. Seems logical enough.

    Michael
    Michael

    One thing to keep in mind is that many DoF scales are rather optimistic (using a very liberal CoC). If you want your image to be more critically sharp, use an f/stop or two less on the scale than what your actual aperture is.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  3. #13
    Mainecoonmaniac's Avatar
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    The DOF will be the same since they're the same focal length. There is a cool Iphone app called Simple DOF Calculator.
    http://www.montanamedia.nl/apps/simple-dof

    I also like using the depth of field preview on cameras also.

  4. #14
    RalphLambrecht's Avatar
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    Quote Originally Posted by Mainecoonmaniac View Post
    ...I also like using the depth of field preview on cameras also.
    That never worked for me.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  5. #15

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    Me either. I can't see anything well once stopped down.

    Regarding optimistic DoF scales, I never really rely on them. They are sometimes useful for a rough idea and then I always stop down further for better sharpness, although I try not to go further than necessary to avoid too much diffraction.

    Thanks

  6. #16

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    The short answer is YES.

    If magnification is the same (magnification being controlled by focal length and distance from the subject), and aperture is the same, depth of field will be the same. That is, if the lenses are focused at the same distance, and prints of the same size and quality are made and viewed at the same distance, the part of the picture that is "acceptably sharp" in front of and behind the plane of critical focus will be the same.

    Tilting the lens, however, will change the orientation of the plane of critical focus, to which the lowly "acceptably sharp" areas are slaves. Therefore, when tilting, you do not change the "depth" of field of the image measured either way from the plane of critical focus, but you do change which parts of the composition fall within by the "acceptably sharp" field.

    So, there are some semantics involved, the definition of D of F being subject to numerous debates. The way I read it, by tilting, you don't actually change the depth of the field of acceptably sharp focus in the image, but you do apparently change it in the print, by way of reorienting it. If D of F is simply defined as "the depth of the acceptably sharp area in a print," then you do change it. If D of F is defined as "the depth of the acceptably sharp area surrounding the plane of critical focus in the image," then you do not.

    However, while the short answer about transferring the D of F from one lens to the other is YES, the more important answer is that you do not want to rely on the D of F scales on lenses to tell you what your D of F will be.
    Last edited by 2F/2F; 05-17-2010 at 08:10 PM. Click to view previous post history.
    2F/2F

    "Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."

    - Rob Tyner (1944 - 1991)

  7. #17
    Lee L's Avatar
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    Quote Originally Posted by Sirius Glass View Post
    For a particular exposure [read; f/stop fixed] and the same image size on the film for close subjects, the depth of field is the same regardless of the focal length of the lens!

    I have posted the detail here of this before.

    Steve
    Others have refuted this often repeated claim, and shown their work.

    http://theonlinephotographer.typepad...he-sequel.html

    Lee

  8. #18

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    That's not a refutation, Lee. Just a demonstration that it is extremely easy to confuse the amount of blur outside the DoF range with the size of the DoF range.

    What changes with focal length is the degree to which blur increases with distance.
    The actual range that falls within DoF however always is the same, given the conditions mentioned by Steve (though he should drop the "for close subjects" bit. It always is. The "for close subjects" thing stems from the confusion of hyperfocal distance with DoF.)

  9. #19
    Lee L's Avatar
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    The article I referred to is by Ctein, not Mike Johnston. An opinion that Johnston's blog is "pretty" doesn't make Ctein wrong.

    I posted this: http://www.apug.org/forums/forum206/...tml#post824775 to a similar thread earlier, which was a way of checking the stated 'rule' against the depth of field spreadsheet provided by Schneider Optics. It supports Ctein's observations.

    There are apparently a couple of folks posting to this thread who are on my ignore list, so I should bow out and let you guys carry on. No need for me to create a lot of confusion and cross-talk. People who are concerned can research things for themselves.

    Lee

  10. #20
    Lee L's Avatar
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    OK, here's one more explanation, cited in the wikipedia article sirius glass cites:

    A rule of thumb for depth of field is:

    Depth of field is the same for all lenses when the image size is constant and the same f-stop is used.


    This rule of thumb is approximately true when the focus distance for the shortest lens is less than about 1/4 of the hyperfocal distance for that lens.

    ... It can be shown mathematically that the rule is not exactly correct for any situation.
    Here's the full article with charts and graphs:
    http://www.dofmaster.com/dof_imagesize.html

    Lee
    Last edited by Lee L; 05-20-2010 at 11:20 AM. Click to view previous post history.

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