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Dof And peaking

Discussion in 'Sony Alpha E-Mount Cameras' started by alaios, Sep 1, 2013.

  1. alaios

    alaios TalkEmount All-Pro

    Jan 11, 2013
    Düsseldorf
    Alex
    Dear all,
    I am using the calculator here

    Online Depth of Field Calculator
    trying to understand how the DOF affects the areas that would be in focus.

    Now lets assume that I am using my Minolta 50mm/1.7 at 1.7. I am focusing at 4 meters to a face, so the calculator says that the region of focus is from 3.8 and 4.22m . So 40 cm. Enough space for shooting portrait (including head) and throwing the rest out of focus.

    What is not very clear still is

    1. How the crop factor of the nex body affects the calculations? Does this calculator take that into account?

    2. Is the crop factor something that just crops the image taken and has nothing to do with the depth of field?

    3. (here we assume that we have perfect conditions for the peaking to show focus correctly, and the peaking is set to red). Now I start by having the lens focused at the shortest distance, lets say 50cm. As my subject is standing at 3 meters it would be out of focus and in reality I would not see on my screen any red lines coming from the peaking.
    Then I start changing the focusing slightly to longer distance.. until the point I see the first red small line of peaking appearing. There I stop. Would I be just entering the far limit of acceptance focus? If someone thinks the near limit of acceptable focus and the far limit of acceptable focus defining a region. How I can be sure with the nex cameras that I have included the head of my portraits within that region?

    I would like to thank you for your replies



    Regards
    Alex
     
  2. xXx1

    xXx1 TalkEmount All-Pro

    Jan 15, 2013
    In theory crop factor doesn't affect depth of field. The term 'Circle of Confusion' is however very meaningful and Nex C3 has got 0.02 mm one.

    In practise things are much different. Generally you magnify crop sensor images more than full frame images so defocus shows more.

    Unfortunately there is no other way than experimenting to get results you want. Too narrow DOF is really bad in portraiture as eyes are perfect to focus but you want the nose to be sharp too.

    I think that Ken Rockwell writes about DOF very well here:
    Crop Factor

    In the calculator you use, you enter crop factor and maybe sensor resolution by choosing camera model.
     
  3. alaios

    alaios TalkEmount All-Pro

    Jan 11, 2013
    Düsseldorf
    Alex
    There is something in the calculator that I am trying to understand. I do not have my camera with me as I am working from office (currently in break).
    have 28-85 lens that at 85 can have an aperture maximum of 4.5... According to the dof calculator I would be able to get a very nice isolated portrait if I am standing at 6 meters. Total Depth of field is 0.89 meters.... So If I understand right I can get some nice isolated portraits even with my zoom lens.. Right? If yes how the bokeh would like is a a matter of the current lens. Is not that right?


    Regards
    A.
     
  4. Ken

    Ken New to TalkEmount

    8
    Aug 1, 2013
    Virginia, USA
    Ken
    "According to the dof calculator I would be able to get a very nice isolated portrait if I am standing at 6 meters. Total Depth of field is 0.89 meters.... So If I understand right I can get some nice isolated portraits even with my zoom lens.. Right?"

    Maybe...

    It depends on how far away the background is from your subject. If the background is 10 meters away, yes, you'd get a nice isolated portrait. But what is the background is only 1/2 meter away? You'd get a nice clear photo of the background, too; it wouldn't necessarily be sharp, but it would be noticable.

    All the depth of field calculator will tell you is the approximate area that will be in acceptable focus - what is does not tell you is how out of focus everything else is.

    You can spend hours studying depth of field tables and all you will do is confuse yourself. Spend the same time shooting at different focal lengths and apertures and you'll find out what works and what doesn't. More importantly, you'll find out what you like and what you don't. After you figure this out, and it will take some time, then go back to the depth of field calculator, and the results will have some meaning to you. Grab your camera, try it and see what happens. Photography is an art, a craft - not a science.

    Maybe you'll find you like the effect of a larger, or smaller, aperture much more than what the calculator tells you. There is no rule or law that says backgrounds and foregrounds must to be completely out of focus. Sometimes a slightly defocused background is much more pleasing than one that is completely out of focus. It's all subjective.

    Also, how much you want out of focus depends on the type of portrait you're taking. It all depends on the purpose of the photo and what you're trying to show.

    As for your question on bokeh, I'm not sure what you're asking. But remember, bokeh is not the same as out of focus. Bokeh is simply the perceived quality of the out of focus highlights, nothing less, nothing more. Do the out of focus highlights have a hard edge or a soft edge? That's all bokeh is. As to whether that particular lens has good or bad bokeh, all you can do is to try it out.
     
  5. xXx1

    xXx1 TalkEmount All-Pro

    Jan 15, 2013
    Unfortunately no. In focus means that image is restricted to circle of confusion. For example with Nex that is 0.02mm circle (roughly one pixel in sensor). That means that sensor doesn't see the image blurred. For humans the image will be in focus for much larger circle of confusion and the transit from in focus to completely out of focus occurs takes a long distance.

    These calculators are very useful only to macro shooters. It is best just experiment. You will learn very soon what aperture to use with what lens and type of photograph. Too narrow DOF makes focusing very critical. For example here focus is wrong about a centimetre:
    http://i1305.photobucket.com/albums/s558/xXxYksi/DSC03376_zps872ce6af.jpg

    Nose is slightly out of focus. I would have preferred tip of nose and eyes to be in focus and ears out of focus.
     
  6. eno789

    eno789 TalkEmount Top Veteran

    720
    Jan 1, 2012
    NoCal, USA
    Brian
    Isolation and background blur is related to DoF, but not determined solely by DoF. The result of the DoF calculator just tells you that the area outside of the DoF band will not be considered sharp.

    The distance between the subject and background is very very important for isolation. All is relative, if your background is far enough, you can definitely get nice isolation with 85mm at f/4.5. You should try it, then you will know why you might like a faster lens for portrait. Then again, for those type of shots that you want more context, you don't want the background to be blurred too much.

    From my experience, crop factor does affect DoF. When everything being equal including the view/print size, the smaller the sensor is, the more DoF you get. That's why you're not getting subject isolation as easily with point-n-shoot. One way to speed up your understanding of DoF/isolation/blur, is to take some close-up and macro picture - since the DoF is very thin the relation is magnified.
     
  7. alaios

    alaios TalkEmount All-Pro

    Jan 11, 2013
    Düsseldorf
    Alex
    Thanks for the answer.. So when you just use the peaking system to focus you just make sure that the red dots cover all the elements you want to include in the frame.. I am getting this right?

    Regards
    Alex
     
  8. xXx1

    xXx1 TalkEmount All-Pro

    Jan 15, 2013
    Yes. For critical shots the magnifying system is very nice. For portraits focusing to eyes works very well, I rotate focusing barrel so that peaking is about middle and focus to eyes. I think that too narrow dof is bad and nailing the focus is difficult so thin dof is reserved to special cases (adults and plenty of time).
     
  9. alaios

    alaios TalkEmount All-Pro

    Jan 11, 2013
    Düsseldorf
    Alex
    Hi,
    I was out today doing some shooting.. I feel sometimes that I am overdoing the isolation for portraits think. I stuck my aperture to 2.8 either to my 100 and 135 to isolate my subject but unfortunately I end up with many areas out of focus and too bad results

    A.
     
  10. xXx1

    xXx1 TalkEmount All-Pro

    Jan 15, 2013
    2.8 is about ok for me with 85 mm and 4 with 135mm. These with head&shoulder shots. Keep on experimenting and remember that focus is critical.
     
  11. Jefenator

    Jefenator TalkEmount Top Veteran

    876
    Nov 23, 2012
    Oregon, USA
    Jeff
    I've never spent much time with the DoF calculator, myself. I'm with Ken - better to get out there and shoot and try a bunch of stuff and see what works and what doesn't.

    I've heard some folks suggest that crop formats actually have less DoF on account of having narrower CoC. That may be so in an extreme pixel peeping context, but when looking at the entire frame I highly doubt that a cropped 35mm is going to yield better subject isolation than an uncropped 50mm. Evidently different CoCs apply for different purposes - if I were inclined I might try to calculate various multiplication factors to account for pixel peeping, large prints, computer screens, etc... Or I could do test shots running a range of apertures and just eyeball it.

    One technical fact I do find handy is that DoF is a factor of magnification and aperture. That is to say, as long as you are framing the same subject the same way (on the same capture format), lens focal length is not a factor. So for me, the real factors are: subject size, composition in the frame and the effect desired. After a year of exploring shallow focus, I have acquired a feel for my preferred aperture settings for certain standard shots.

    For instance, when I want to fill the frame with a mostly-in-focus 6" vase and have a nice, blurred background, f/5.6 or f/8 is usually best, regardless of whether I am using my 35mm, 60mm or 100mm lens. (A longer lens does provide a narrower view on the background, which usually helps reduce distraction.) In the studio, trying to get maximum sharpness across the entire subject, I've settled on f/16 (occasionally f/22 but diffraction does become more noticeable).

    Those are for my standard product shots which I do by the hundreds. For other types of shots, I'm still feeling it out. (For an unfamiliar scene, I like to bracket aperture settings when possible, and I take full advantage of the bright stopped-down live view.)

    IME peaking can be super handy but you do have to know when you can and cannot rely on it. For certain scenes where there is a lot of contrast occurring naturally, it has mislead me pretty badly. Whenever time permits, I like to use MF Assist. (One of the key features on the NEX-7 for me is the ability to engage MF Assist with a very handy button, then go back to the frame with a quick shutter half-press.)
     
  12. alaios

    alaios TalkEmount All-Pro

    Jan 11, 2013
    Düsseldorf
    Alex
    Thanks for the tip.. perhaps the 2.8 as you said is too short for the 135mm.... I did not have troubles though focusing with my 50mm at 1.7 and 2.8. I guess is also the lens that makes focusing easier as is wider. Right?

    A
     
  13. xXx1

    xXx1 TalkEmount All-Pro

    Jan 15, 2013
    Yes. Narrow DoF makes focusing technically easier. In the old bad days we did focus wide open and camera did stopping down for us.

    But as I sad, don't try to make DoF too narrow.
     
  14. alaios

    alaios TalkEmount All-Pro

    Jan 11, 2013
    Düsseldorf
    Alex
    Hi and thanks for the answer. I am learning quite a lot already and thanks for that.
    The DOF calculator indeed gives you very good understanding of different focal lengths, at different focus distances and DOF.

    What is not clear though is
    1. What is considered as acceptable focus? Is this lens specific? Or taste specific of the photographer?
    2. What happens out of the DOF region? Is this lens specific?
    3. How fast the lost of focus takes place?

    Regards
    A
     
  15. Gandalf

    Gandalf TalkEmount Regular

    59
    Sep 5, 2013
    Depth of Field is defined mathematically, and is also subjective.

    To begin: DOF calculations are based on the resolution of the human eye. That in itself makes it subjective, because not everyone's eyes are the same. Somewhere in the dark past of photographic history, someone figured out how to determine if something would be in focus, or not. Certain assumptions must be made, and it's critical to remember that whether we like (or agree) with those assumptions will not change the equations. We're going to assume a "standard" print size, viewed at a "standard" distance, and seen by "standard" eyeballs. Whether (or not) we actually make prints of this size, or any size, or view them at a different distance, is irrelevant, because these are assumptions that were made long ago in deriving the depth of field formulas.

    1st ASSUMPTION: It is assumed that we are going to make an 8x10 (inch) print.
    2nd ASSUMPTION: Our 8x10 print will be viewed at a standard viewing distance. This distance is assumed to be 12 inches away from your eyes.
    3rd ASSUMPTION: Average human eyesight makes it possible to resolve two points that are 0.2mm apart, when viewed at a distance of 12 inches.

    What these assumptions tell us, is that if we make a print and view it from 12 inches away, a blurry blob in the print that is 0.2mm wide (or less) will be seen as a single point because that is the smallest detail that the eye can resolve. So our goal when we want to have stuff in focus, is to make it so that everything we need in focus will be blurred no more than 0.2mm in our final 8x10 print which we will view from 12 inches away.

    This blurry spot is mor commonly known as a "circle of confusion." So we are allowed a CoC of 0.2mm in the 8x10 print, but if our recording format is smaller than 8x10 we will require more precision in the camera!

    If we are using an 8x10 camera (where the film is actually 8x10 inches) then we can allow a CoC equal to the allowable blur in the final print: 0.2mm.
    In a 4x5 camera, the image on the film must be enlarged 2X to make an 8x10 print, so we are limited to a 0.1mm circle of confusion on 4xx5 film.
    Moving past a bunch of medium formats and onward to our small formats; on 35mm (full frame) it works out to about 0.03mm, and so when we get to the APS-C format we're limited to a 0.02mm circle of confusion on the sensor. That's because the APS-C image will be enlarged roughly 10 times to make an 8x10 print, so the 0.02mm CoC in the camera blows up to 0.2mm on the print.

    For prints larger than 8x10, it is generally assumed that the viewing distance increases at least proportionally to the print size. It's assumed that a 16x20 will be viewed at 24 inches, so the DOF calculations remain the same. If these factors, or the viewer's eyes, differ appreciably from the assumed norms, then you adjust the circle of confusion until the output of the DOF formula agrees with the perceived focus in the final output.


    Going back to the original questions in this thread... yes, the calculator takes the so-called "crop factor" into account (I hate that term, never mind that it has become the standard means of comparing cameras) and yes, the size of the format ("crop factor") has everything to do with depth of field. Selecting a particular camera or format in the online calculator is just a way of plugging the appropriate circle of confusion into the DOF formula.


    1. See the assumptions about what the viewer is looking at. If the viewer's eyes are better than what the formulas assume, then you'll need to use a smaller CoC to calculate the DOF. Likewise, bad eyes mean you can be a bit sloppier and the viewer will still perceive things as being in focus. Here's where you may find a definite advantage in having an audience of old geezers like me, who can't see stuff half the time.

    2. How things devolve outside the zone of focus does vary somewhat depending on the lens and how it is constructed. Usually referred to as "bokeh" but we're not gonna go there.

    3. The increase in size of the circle of confusion as objects in the subject space get farther away from the plane of focus will be mirrored linearly in the image space. In other words, it's a linear thing, but again depends somewhat on the lens construction, and a lot on the person viewing the image.


    So depth of field can be calculated rigorously and held to tight mathematical tolerances, and then it all goes out the window because your conditions don't quite match the "givens" in the original formulas. DOF calculations are a great place to start, but ultimately it comes down to what you see when you look at your final image.
     
  16. Bimjo

    Bimjo Super Moderator

    Oct 28, 2011
    Washington State
    Jim
    Welcome to the forum Gandalf, great first post.