DOF in viewfinder different from captured image!

Discussion in 'Digital SLR' started by Hussam, Sep 25, 2005.

  1. Hussam

    Hussam Guest

    This is weird.. I have a Nikon D70s.. just picked it up the other day..
    my first DSLR (after using a Nikon FE-2).. so i put on my 50mm 1.4 AiS
    lens and look through the viewfinder.. and things pretty much look
    focused.. like as if i'm at f4 or f5.6.. i click the shutter (aperture
    set at f1.4) and the captured image has shallow depth of field - as
    expected at f1.4... but how come what i see through the viewfinder is
    not the same?!!!!

    Same story with my 35-135mm f3.5-3.5 AiS lens.. when i put it on.. and
    take a picture at 3.5, it's different than what i'm seeing in the
    viewfinder... the viewfinder image is again more like f5.6 ...

    what's up with that??

    Thanks for any insight.

    p.s. i don't seem to have this problem with the AF-S 17-80mm DX (kit)
    lens.. but then again.. its maximum aperture is already at f4.5..
     
    Hussam, Sep 25, 2005
    #1
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  2. That is how it has always been. Which is why some camera have a DOF
    preview button.

    http://photonotes.org/cgi-bin/entry.pl?id=Depthoffieldpreview
    http://www.photozone.de/3Technology/demos/DOFbutton.htm
    http://www.naturephotographers.net/articles0905/rb0905-1.html
    http://www.hoothollow.com/QofM2002-2003/Question-OctoberNovember2002.html

    But it is pretty much useless for reasons you will read.

    You have to use your brains.

    You might also ask why your view finder does not get darker when the
    scene is under exposed. :^)
     
    Christian Bonanno, Sep 25, 2005
    #2
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  3. Hussam

    Hussam Guest

    No I don't think you get it.. the viewfinder is supposed to show me DOF
    equivalent to f1.4 if my attached lens is 50mm f1.4!.. likewise, if my
    other lens stops down to f3.5 then that's what i should see through the
    viewfinder.. regardless of what actual aperture i end up shooting at..

    but what i'm saying is, that even with my 50mm f1.4 lens, what i'm
    seenig through the viewfinder is something more like f5.6.. the f5.6
    should only end up on film (or ccd) but NOT in the viewfinder UNLESS i
    engaged the DOF preview button...

    I hope i'm clear....
     
    Hussam, Sep 25, 2005
    #3
  4. Hussam

    Pepe Guest

    It seams like you aperture is not working well when on the camera.
    Perhaps there is lagging when the camera should bring the aperture to f1:1,4
    Thats what it should normaly do when attached to the camera housing.
    If not, it will be as you describe dark in the veiw finder.

    Make sure there is no oil on the aperture blades, commond on old objektivs.

    Pepe
     
    Pepe, Sep 25, 2005
    #4
  5. Hussam

    Frank ess Guest

    Take the picture, shrink it to the relative size of your viewfinder
    and judge the difference in focus between the in-DOF and out-of-DOF
    features. Could it be the scale of the viewfinder doesn't allow useful
    discriminations on wide-open, low-F views?
     
    Frank ess, Sep 25, 2005
    #5
  6. Hussam

    wilt Guest

    Not intimately familiar with the D70, but a long time ago with
    twin-lens reflexes point and shoots, the aerial image thru the aiming
    lens was nice and bright and easy to see. Just point and shoot and
    don't worry about focus. Everything was sharp in these finders!
    Then SLRs came about, and groundglass was employed so that the entire
    screen could be focused, but not with enough precision, so focusing
    aids like split screen and microprism were added to improve focus
    acuity. But with the precision can darkening of the central focusing
    aide. Then manufacturers introduced exchangeable focusing screens, so
    that you could have enough focus precision for a long focal length lens
    without the screen darkening horribly.
    Now comes the autofocus SLR...the manufacturers begin with very bright
    focusing screens that are near useless for manual focus, but when
    photographers mount manual focus lenses they suddenly want some
    focusing precision, but not all the SLRs are optimized for that...they
    still use nice bright finders and focusing screens, but somewhat like
    the old aerial images fo the TLR point and shoot...so they show a lot
    of stuff in focus because the screens are designed to be bright, and
    that is counter to showing things sharp vs. somewhat unfocused for DOF
    evaluation.
     
    wilt, Sep 25, 2005
    #6
  7. Never has this problem with my early Nikons and later the Contarex
    with it's fresnel focusing screen with a microprism ring around the
    split prism.

    So? You just put in a focusing screen that supports good manual
    focus.

    Canon has several for the 1 bodies and there are third party solutions
    for the low end Canons.

    The real problem with most DSLR's is found in the small sensor and the
    lack of a true pentaprism.
    *********************************************************

    "I have been a witness, and these pictures are
    my testimony. The events I have recorded should
    not be forgotten and must not be repeated."

    -James Nachtwey-
    http://www.jamesnachtwey.com/
     
    John A. Stovall, Sep 25, 2005
    #7
  8. Hussam

    no_name Guest

    The brain provides depth of field the camera lens cannot.
     
    no_name, Sep 26, 2005
    #8
  9. You're clear but you're wrong and confused. Please don't snip so much
    of the post in the future.

    You said:
    You wanted to know why what you saw in the view finder ("like as if i'm
    at f4 or f5.6") does not look like the finished image (" shallow depth
    of field as expected at f1.4 but how come what i see through the
    viewfinder is not the same?!").
    FIrst I want to ask you how you can judge DOF that precisely.

    You have not said what distance the object you are focusing on is, which
    also has an effect on DOF.

    Oh, and don't go by the view finder. Tell us about the digital image.

    But you communicated it all poorly. Maybe try again. Be very specific
    with everything, limit the variables.
     
    Christian Bonanno, Sep 26, 2005
    #9
  10. Hussam

    DoN. Nichols Guest

    I think that what you are seeing is that your eye can correct
    for minor out-of-focus condition in the viewfinder, especially without
    an anchor. If you turn on the autofocus zone display ("pencil" menu,
    item 18 "AF are illm") and the grid in the viewfinder (same menu, entry
    08 "Grid Display", you have anchor points for your eye's focus, so you
    should compare the apparent focus in the viewfinder while the grid or
    the autofocus zone indicator are sharp in your vision.

    But in any case, you don't have the full-screen ground glass
    viewfinder area which was used back in the Nikon F days to give a better
    indication of the depth of field. And you are trying to compare a tiny
    image in the viewfinder with the much larger image display on your
    computer's screen, or a printed copy from a printer. Depth-Of-Field is
    a function of image size, and what is sharp enough in a tiny image may
    well no longer be so in a larger image.

    Also -- are you in "Auto" mode on the top dial to the left of
    the pentaprism? If so, it will select whatever portion of your image is
    the closest, and autofocus on that. Switch to "P"rogram mode, and it
    will use the autofocus zone which you have selected, while most other
    features remain as automatic as you may need. (Or were you switching
    off the autofocus on the camera body, and attempting manual focusing?)

    Enjoy,
    DoN.
     
    DoN. Nichols, Sep 26, 2005
    #10
  11. Hussam

    DoN. Nichols Guest

    Of course -- they were designed for *manual* focusing, as
    autofocus did not exist at the time. They also had changeable focusing
    screens because a microprism and split image which worked well with
    wide angle lenses would not work so well with a telephoto and vice
    versa -- as well as allowing you to select focusing screens better for a
    given set of conditions.

    IIRC, the screens for the Nikon F where this mattered came in
    four different focal length ranges, to adapt to your lens focal length
    range.

    For critical focus with really long lenses, or for working
    through a microscope, there was a plain ground glass screen (which would
    work equally dimly with all focal lengths) with a clear center spot with
    a fine '+' in the center. If you moved your head from side to side
    behind the viewfinder (assuming a rigidly mounted camera, of course), if
    the center area were truly in focus, you would see no relative motion
    between the '+' and the image. However, the more out of focus it was,
    the more relative motions was visible. This would work when any of the
    split image or microprism screens would not.
    Easy to say. However, the D70 (and presumably the D70s) does
    not have interchangeable focusing screens -- at least in part because
    the autofocus depends on special microprisms oriented to concentrate on
    the autofocus sensors, not on the user's eye. Also, the focusing screen
    has a lot of active electro-optical displays on it, such things as the
    autofocus zone indicators and the grid which can be switched on and off.
    That means a lot of interconnections, which could make problems with
    contact quality every time you changed focusing screens.
    Is this true for the Cannon DSLRs? If so, does the Cannon DSLR
    also have active displays on the focusing screen as the Nikon does?

    Enjoy,
    DoN.
     
    DoN. Nichols, Sep 26, 2005
    #11
  12. Hussam

    Jeremy Nixon Guest

    The active LCD displays are separate from the focusing screen. The Nikon
    D2x has interchangeable focusing screens; if you replace it, the active
    displays (focus area indicators) still work. The stock screen has crop
    lines for the "high speed crop" mode area; they also give you an alternate
    one with the camera that doesn't have those. I swapped them out since I
    never use "high speed crop" mode.

    Unfortunately, there aren't any focusing screens available for the camera
    with manual focus aids.
     
    Jeremy Nixon, Sep 26, 2005
    #12
  13. Hussam

    Drifter Guest

    I may not be much help here, I use Canon so don't have much specific
    experience with Nikon. Having said that, most Canon equipment has an
    "aperture preview" button. In other words you set your aperture but
    you will see nothing happen in the viewfinder. What's happening is
    that the aperture is staying pretty open to allow maximum light in so
    that you can see to focus. If you really want to see what effect the
    aperture is going to have you need to press the "aperture preview"
    button (to really check DOF and so forth).

    I don't know if Nikon does it the same way.

    Drifter
    "I've been here, I've been there..."
     
    Drifter, Sep 26, 2005
    #13
  14. Hussam

    Paul J Gans Guest

    Which is why film SLRs had a special viewfinder screen with
    focussing aids. Many will remember those. They were needed
    for just this reason.

    It is too bad that dSLRs do not have the same feature. As
    a result it is almost impossible to manually focus one. Of
    course the automatic focus is supposed to take care of that,
    but there are a number of low contrast situations where the
    human eye is better than the electronics.

    But no matter. The explanation is as Frank says. Many a
    precious shot has been saved by NOT printing it at 8x10
    but using something smaller instead.

    ---- Paul J. Gans
     
    Paul J Gans, Sep 26, 2005
    #14
  15. On 26 Sep 2005 02:13:26 GMT, (DoN. Nichols)
    wrote:

    snipped
    http://www.dpreview.com/news/0508/05082208canoneos1dmkiin.asp

    The camera’s focusing screens are interchangeable; an optional new
    “Super Precision Matte” Ec-S focusing screen enables easier manual
    focusing with fast lenses.

    http://www.bhphotovideo.com/bnh/controller/home?O=breadCrumb&A=search&Q=&ci=4662

    If you want to buy some.


    *********************************************************

    "I have been a witness, and these pictures are
    my testimony. The events I have recorded should
    not be forgotten and must not be repeated."

    -James Nachtwey-
    http://www.jamesnachtwey.com/
     
    John A. Stovall, Sep 26, 2005
    #15
  16. Hussam

    Alan Browne Guest

    The viewfinder is quite small, so there is not enough detail available
    to really determine what will be sharp in the final image.

    DOF preview, DOF markings and DOF calculations are guides.
     
    Alan Browne, Sep 26, 2005
    #16
  17. Hussam

    Hussam Guest

    The aperture is working fine... the viewfinder is nice and bright.. the
    lens is NOT stopped down... but looking thru the viewfinder the depth
    of field is "deeper" than captured image even though i'm shooting at
    f1.4 (or f3.5 in the case of the other lens).....
     
    Hussam, Sep 26, 2005
    #17
  18. Hussam

    Hussam Guest

    that's deep...
     
    Hussam, Sep 26, 2005
    #18
  19. Hussam

    Hussam Guest

    HI.. thanks for your thorough reply... I'm comparing the image in the
    viewfinder to the image on the lcd ... it's not that hard to tell the
    difference between an f1.4 and an f5.6 image.. i'm focusing at
    something that's about 2 meters away and looking at a background that
    is about 4-5 meters away.... you can tell the difference.

    Also, with non-CPU lenses (as is the case with my manual focus 50mm and
    35-135mm lenses), you MUST use Manual mode on the D70s... so i wasn't
    on Auto.

    I THINK the explanation is the diopter adjustment messing with the
    image in the viewfinder.. making it sharper than what it really is..?
    i'll check.
     
    Hussam, Sep 26, 2005
    #19
  20. Hussam

    Hussam Guest

    I'm not wrong.. but confused yes... that's why i posted my question.

    As to how i can judge DOF that precisely... it's not that hard to tell
    the difference between f1.4 and f5.6.. the difference is pretty big!
    You don't need super vision for that.

    Sorry for not specifying what distance i was focusing at.. didn't think
    it made a difference...i was focusing at 2 meters with the background
    being at 4-5 meters.

    What do you mean don't go by the viewfinder..i'm using an SLR!!! what
    else am i supposed to go by?!!!
     
    Hussam, Sep 26, 2005
    #20
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