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The balance between high resolution and DOF

Discussion in 'Lens Lust' started by Steinar, Jul 30, 2008.

  1. Steinar

    Steinar

    Aug 16, 2007
    Denmark
    If you want to shoot landscapes you want to have a huge/sharp DOF, so as much as possibly is sharp.

    So therefore you will shoot at low aperture - example f/8 or more/lower.

    (Please forget the diffraction a little for this question).

    But there is a balance between the aperture and the resolution.

    Just for the example I have chosen the Nikon 70-200 VR at 70mm (and it is wonderfull sharp on a D200, so I would use it for scapes at 70mm).

    Look here at photozone:


    http://www.photozone.de/nikon--nikk...mm-f28-g-if-ed-vr-review--test-report?start=1

    You will see, that the resolution is best at f/5.6 and lower resolution at f/8, but the DOF is better for scapes at f/8.

    So you get a better DOF, but lower resolution, by changing the aperture from 5.6 to 8.

    That will say:

    At f/8,0 there is better DOF, but the resolution is lower.

    My question is:

    Where are the balance - can you say something about that.??

    I usually find out where the best resolution of my lenses are and shoot at that aperture, well, maybe a little lower, but I am in doubt if that is right, because I get a better DOF stopping more down.

    I am here thinking about large prints of scapes.
     
  2. Looking at the numbers at Photozone, I would go with DOF and not worry about the resolution. If your copy is as good as it is rated, I would think you would have trouble seeing the resolution difference in 1 stop. You may see the difference in DOF though.

    If you already have that lens, why not set up a test and see for yourself if you can tell the difference? I have the predecessor (80-200 f2.8), and may try that myself.
     
  3. Steinar

    Steinar

    Aug 16, 2007
    Denmark
    Thank you, yes I could, but I also shoot scapes with Tokina 11-16, Nikon 35-70 f/2.8 and also sometimes Nikon 10,5 fisheye, and if I go FX I think I also will use my 50mm f/1.8 for scapes (do not use it now, because I do not love the 50mm on DX) so my question is not only for the 70-200VR, but a generel question, if somebody could say something about that balance.

    But I think you are right for about 1 stop, and I do it, but I began thinking about it, because I got an assignment for a landscape a certain place, and it should be a large print 40 x 60 cm, and we begin to meet the D200.s limitations, I think.

    And I think there must be a balance between the resolution and the DOF for large prints.
     
  4. rvink

    rvink

    Mar 21, 2006
    New Zealand
    The resolution at f8 is only a little lower than f5.6, so objects which are in focus will be nearly as sharp. However, objects which are out of focus will be 1.4x more "focused" than before, so if your scene has a lot of depth, the overall sharpness will be greater than the picture shot at f8, even though the peak sharpness at the focus plane will be slightly lower.

    Going further, if you take the same picture at f11, the sharpness at the focus plane will drop further, but the DOF will be twice as great compared to f5.6, and defocus blurs for out of focus subjects will be only half the diameter (quarter the size) so again, the overall sharpness will appear greater. Of course, if you stop down too far, you may end up with more DOF than you need and overall sharpness will be lost due to diffraction.

    My rule of thumb for landscapes is to use the "sweet spot" for the lens - usually f5.6 or f8 for any lens if DOF is not a consideration. If I want to isolate a subject using a narrower DOF, open up only as much as is required to maintain sharpness and DOF on the subject while throwing the background out of focus enough. If you want more DOF, stop down only enough to achieve front to rear sharpness and no further. Of course, what is "sharp enough" within the DOF is a subjective consideration. I usually find the DOF marks too generous if I use them to find the hyperfocal distance for landscape shots. If I'm shooting at f11 I usually use the DOF marks for F16 or f22 to maintain adequate sharpness at infinity.

    Also remember, sharpness is not everything, otherwise you'd shoot every picture at f5.6 or f8.
     
  5. Steinar

    Steinar

    Aug 16, 2007
    Denmark
    Thank you VERY MUCH for this explanation, RVINK.

    It was exactly what I needed - there certainly is a balance - also before the diffraction sets in.

    My former "intepretation" was: If the sweet spot (the highest resolution accordring to the MTF) was 5.6 I gave it about 7.1 just to be sure the DOF was OK (for scapes when I wanted as much as possibly to be sharp without lower the resolution to much), but I was not sure if I did it right.

    My assignment here is a lake, and I know he wants it as a sharp landscape pic and if I use my Tokine 11-16 it would be the right to use f/8.0


    http://www.photozone.de/canon-eos/379-tokina_1116_28_canon?start=1


    (I know it is tested on a Canon, but it is about the same)


    But generel talking:

    For landscapes use the highest resolution and then maybe a stop more (also as the biker said), but not lower than a stop... plus: I think important: The highest resolution should - for the best for scapes - for the lens be about 5.6 or lower if you want large prints.

    Agree ?

    ---

    Of course you can always say, that if you interpretate, that the resolution is high enough at f/11.0 (and no diffraction)then it is OK
    to shoot here, but if you can use the high resolution, about where it is best, then it would be better.
     
  6. pforsell

    pforsell

    Jan 15, 2008
    Hi Steinar,
    the loss of resolution at smaller apertures is not an abrupt change. The sharpness of the lens does not collapse suddenly but instead slopes gradually.

    2718365239_5a4e81eaeb_o.
     
    Last edited by a moderator: Jul 31, 2008
  7. cotdt

    cotdt

    Jul 14, 2007
    Bay Area, USA
    you could always shoot at f/5.6 at multiple focus distances, and later stitch the images together.
     
  8. Steinar

    Steinar

    Aug 16, 2007
    Denmark
    Hi Peter

    That is a very good "picture", that really says it - more clear, than the curves, but reading it together with the MTF-curves is very informative and for some lenses you could lower it more than 1 stop, I can see.

    -----

    Hi Cotdt

    Never tryed it - but very good idea - using the tripod.


    ----


    Thank you both.


    Best from Denmark


    Steinar
     
  9. The 70-200mm VR is about optimal for the purpose you stated at F/11. At higher F-numbers, diffraction will slowly degrade the resolution and then linearly with F-number after a couple of stops more.

    Regards,
     
  10. Steinar

    Steinar

    Aug 16, 2007
    Denmark
    Yes, thank you, Barry, at f/16 there is very low resolution, and the diffraction sets i even before that.
     
  11. Peter, is the curve you posted for a particular lens, or just a general illustration?

    Steinar, maybe I'm not sure what type of landscape you are shooting, but I seldom find that DOF is an issue in landscape shots. The subject is generally too distant for that.

    However, if you have something in the foreground to add interest, then of course DOF is an issue. But I usually find that it is impossible to get both a foreground object and the background to be in focus in those situations. I think the rule here is to be sure the foreground object is in focus, or it will be a distraction.
     
  12. Steinar

    Steinar

    Aug 16, 2007
    Denmark
    Hi Jim, I always or nearly always have a foreground, and I will have in the assignment, but you are right the challenge is here to get both the foreground and the background OK.

    I use the simple 1/3 and 2/3-rule (sharp 1/3 before the focus and 2/3 after the focus) ), and it usually works.




    2537489557_5382b9828a_b.



    -----

    I think the issue you mention here could be solved with a PC-lens.

    ---

    On a IR-photo the DOF nearly always looks fine, but it has something to do with the IR - the haze dissapears with the IR.



    2675078266_6c24b1ee1d_b.
     
  13. Steinar

    Steinar

    Aug 16, 2007
    Denmark
    ""Peter, is the curve you posted for a particular lens, or just a general illustration?""


    I am also very interested in that.
     
  14. rvink

    rvink

    Mar 21, 2006
    New Zealand
    It is difficult to make any rules about which aperture is the best for any scene as it depends on a lot of factors.
    - How big will you print the image? A small print may look sharp enough, but for enlargements you may need to use a smaller aperture to get sufficient DOF and sharpness.
    - How sharp is sharp? Do you eyeball your prints very closely to see the finest detail, or view them from further back? What is sharp to one person is slightly soft to another.
    - Do you want the DOF to extend to infinity? Or do you want the horizon to be slightly soft to give emphasis to the subject in the foreground?
    - The situation is further complicated by certain lens aberrations such as longitudinal CA, which may blur and smear colors away from the focus plane, resulting in less DOF than you might expect.

    Assuming you want to make large prints with near to far sharpness, you should be focusing at the hyperfocal distance - set the aperture and turn the focus ring so infinity aligns with the corresponding DOF mark. That focus distance gives you the maximum possible DOF with nothing wasted beyond infinity. The best lenses to use are AI - they have a well spread out focus scale and excellent DOF marks. Unfortunately most zooms completely lack DOF marks or the focus scale is too compressed to be much use here so finding the hyperfocal distance can be rather hit-and-miss (camera makers should really introduce a "hyperfocus" AF focus mode which sets the correct focus distance for the given aperture, focal length and circle of confusion).

    Given the other considerations, the best course is to make a "best guess" and then bracket. If you think f5.6 will give you enough DOF and the sharpest image, shoot at that aperture, then shoot the same image at f8, f11 and f16 (easy to do with digital). One way or another it will ensure you get the best shot for the scene.
     
  15. Steinar

    Steinar

    Aug 16, 2007
    Denmark
    Thank you RVINK - yes new lenses do not have those DOF marks, so I think your last advice:


    "If you think f5.6 will give you enough DOF and the sharpest image, shoot at that aperture, then shoot the same image at f8, f11 and f16"


    ....is the way to go.


    Best from Denmark



    Steinar
     
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