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Thread: Debunking the DSLR FLM Myth and Misconceptions

  1. #21
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    Wow, I gotta say we really got a circle of Confusion now - as in a group of photogs getting confused over DoF!



    Regards
    CK

  2. #22
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    *groan*

    ... at a loss for words ...

    Let me go back to why I did this test - which is basically to clarify that a 50mm lens (or whatever) on a DSLR does NOT equal to a 75mm (or whatever FLM that particular DSLR has) lens on a 35mm film SLR in terms of DOF.

    And that given the same subject to film plane distances, the resultant image has the SAME DOF, notwithstanding that one image will be larger than the other.

    If any of that equation changes, eg, moving the film SLR closer to the subject to approximate DSLR FOV, then the DOF will obviously change. Similiarly if u change the lens on the film SLR.

    When I say same DOF, I mean that the distinctness (or indistinctness) of the background in both DSLR and film images are roughly the same.

  3. #23
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    I know... the current prob I have explaining is that CoC was a term for glass, but now it's been expanded to include any tolerance for *anything* to do with the dot size of the image, vs the original meaning where it's the minimum distortion/max focus of each physical light ray AFTER passing through the optics.
    becos the lens' CoC is constant, ie it's maximum quality of the glass. so it's supplied DoF is always constant.
    but CoC for film and ccd are different, the sqrt(FLM) will be the extra DoF to a CCD becos it can see finer...
    therefore it's right for the wrong reasons. so if u can use super slide film like velvia 50 the CoC is probably the same or close to digital.
    I have not changed my stand though becos CoC of the glass is still the same, and I still believe subject matter's ratio to DoF is more impt than sensor's CoC ratio, which is quite strange (see my 2mp argument). Was just trying to substantiate or bridge the view ck and reflecx have about CoC... which is that the resolvable difference of dot vs circle is highly dependent on the sensor type.
    while I have gained another understanding from reading the inks from reflecx, I believe the use of constant CoC + const 8"x10" is rubbish, cos that's like using 2mp vs 3 mp vs 4mp to say which has better DoF...

    I believe the term CoC has deviated in application, hence each applies it to any *light ray variance* as CoC. so I ahem did that too by calling everything CoC too...

    can see? or totally off my freq already?
    "I'm... dreaming... of a wide... angle~
    Just like the ones I used to know~"

  4. #24
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    (PDoF, PalmOS)

    50mm f/2 at
    1m
    near : 0.975m
    far : 1.025m
    5m
    4.422m/5.751m
    10m
    7.919m/13.562m

    61.24 mm etc (50 x sqrt(1.5)) 1.5 is a direct area-area ratio
    1m
    near: 0.983m
    far : 1.016m
    5m
    4.6m/5.475m
    10m
    8.511m/12.119m

    how's this?
    "I'm... dreaming... of a wide... angle~
    Just like the ones I used to know~"

  5. #25
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    Originally posted by denizenx
    I know... the current prob I have explaining is that CoC was a term for glass, but now it's been expanded to include any tolerance for *anything* to do with the dot size of the image, vs the original meaning where it's the minimum distortion/max focus of each physical light ray AFTER passing through the optics.
    becos the lens' CoC is constant, ie it's maximum quality of the glass. so it's supplied DoF is always constant.
    but CoC for film and ccd are different, the sqrt(FLM) will be the extra DoF to a CCD becos it can see finer...
    therefore it's right for the wrong reasons. so if u can use super slide film like velvia 50 the CoC is probably the same or close to digital.
    I have not changed my stand though becos CoC of the glass is still the same, and I still believe subject matter's ratio to DoF is more impt than sensor's CoC ratio, which is quite strange (see my 2mp argument). Was just trying to substantiate or bridge the view ck and reflecx have about CoC... which is that the resolvable difference of dot vs circle is highly dependent on the sensor type.
    while I have gained another understanding from reading the inks from reflecx, I believe the use of constant CoC + const 8"x10" is rubbish, cos that's like using 2mp vs 3 mp vs 4mp to say which has better DoF...

    I believe the term CoC has deviated in application, hence each applies it to any *light ray variance* as CoC. so I ahem did that too by calling everything CoC too...

    can see? or totally off my freq already?
    CoC is not only a property of glass, but also related to image size, since the CoC affects the level of acceptable sharpness in the image.

    Regards
    CK

  6. #26
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    haha that's why becos by adding ccd photosite size and pixels, suddenly the normal values dun hold static anymore... everything must recalculate...
    tired of saying more, since DoF, perspective and grain/noise characteristics blah blah blah all diff between ccd and film...
    so in the end just ignore it and conc on the subject matter under individual conditions... lol
    maybe wait until some guy gets a 1Ds then we bug him... ;V

    hmm maybe I'll ask mr reichmann of LL wahahaha... he's got the 1Ds...
    "I'm... dreaming... of a wide... angle~
    Just like the ones I used to know~"

  7. #27
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    maybe I should think less shoot more... but it rains like crazy, and idle minds are devil's glee..
    "I'm... dreaming... of a wide... angle~
    Just like the ones I used to know~"

  8. #28

    Default maybe this will help?

    read here



    argent2

  9. #29
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    It is pure physics. A certain lens has a fixed DOF (when using a fixed aperture) when focused at a fixed distance because the same light ray is going through the same amount of reflection and refraction. It has nothing to do with DoC or the size of the film or ccd. I was surprise to see the DOF calculator has different DOF for 35mm film vs ASP film. Therefore Darren is right that the DOF is the same for F5 and D1x when the distance and f value of the subject is the same (of course the amount of content captured are different). This is what I learnt when I study physics (my major subject) in school.

    The confusion comes when you want to capture the same amount of content at a fixed location. If you use F5, you use 50mm lens. If you use Hassy, you need a 80mm lens and if you use D1x, you properly need a 35mm lens. Then the DOF of all these lense are diffenent at the same location using the same aperture (say f5.6).

  10. #30

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    Hey, I know this is an old thread, but Megaweb just pointed out this detailed article http://www.photo.net/learn/optics/dofdigital/ that explains it well.

  11. #31
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    Just curious, if both are usiing the same lens, then both must have the same DOF. even those D1x have 1.5FOV, but it still using 50mm, and the different is the CCD sensor only take 1.5 cropping....I shld have the same DOF....

  12. #32

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    Originally posted by longman
    Just curious, if both are usiing the same lens, then both must have the same DOF. even those D1x have 1.5FOV, but it still using 50mm, and the different is the CCD sensor only take 1.5 cropping....I shld have the same DOF....
    You would get the same DOF only if you crop the full frame image, which is what Darren did.

    On a 1.5x FLM camera, you end up with a different field of view and a different image compared to a full frame image. The DOF difference comes when you have to enlarge the two images by different magnifications to get the same sized print.

  13. #33

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    FYI... photo.net has a new article on this topic.

    Read it here

  14. #34

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    Originally posted by Darren
    *groan*

    ... at a loss for words ...

    You know, there always *will* be confused people. And the worst part is, sometimes, people who seems to be clarified already, will again be *confused* when they meet *unclarified* people.

    Like I am now thoroghly confused...haha

  15. #35
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    Originally posted by Shadus
    Like I am now thoroghly confused...haha
    actually so am i... been following the threads but i still don't totally get it... no wonder they have the term "Circle of Confusion".

  16. #36
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    thx....got the point liao

  17. #37

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    ok lah; i believe the photo.net article by Mr Bob Atkins is technically correct...maybe we should just read it through and understand it all and stick by its rules..thats provided u agree

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