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Focus scale

Discussion in 'Native Lenses' started by rich00, Feb 26, 2012.

  1. rich00

    rich00 Mu-43 Veteran

    251
    Dec 8, 2011
    Hi all,
    Just wondering why most of the native lenses don't have a focus scale ?I've just started playing with legacy lenses and read into theory of depth of field and hyperfocal distance. Now realised how to use those markings on the lens barrel. I suppose AF may removed the need, then again sometimes AF doesn't focus where you want it to and I guess this is where the focus scale would be handy. Is focus scale really a thing of the past or is there other techniques that provide the same result?
     
  2. speedandstyle

    speedandstyle Mu-43 Hall of Famer

    The removal is mostly a cost thing along with a more pleasing aesthetic for the common buyer. Nikon and Canon do not put the scale on their lower end lenses anymore either. Few people actually use the scales anymore.
     
  3. rich00

    rich00 Mu-43 Veteran

    251
    Dec 8, 2011
    That's a shame. There is one instance when I just bought my camera and was at a cycling event and had the AF on and the shots were all over the place. Had I known about DOF and used manual with a focus scale, most of my shots would have been in focus. The cyclists were riding past in fairly consistent line. I guess this part of the learning experience.
     
  4. grantb

    grantb Mu-43 Veteran

    I get the best results from prefocusing on something at the same distance, often the ground where my subject is about to pass.

    A focus scale isn't possible on continuous focus ring lenses unless you do something tricky like on the the (costly) 12/f2.
     
  5. Ned

    Ned Mu-43 Legend

    Jul 18, 2010
    Alberta, Canada
    Most of the Olympus Four-Thirds lenses use fly-by-wire focus except for the SWD lenses. Most of them do have distance scales, except for the Standard Grade.
     
  6. speedandstyle

    speedandstyle Mu-43 Hall of Famer

    What AF mode did you use? Depending on the camera model there are different ways the AF will pick where to focus. For action I prefer center spot and prefocus if I can. Some of the 3d AF setups work well with action.
     
  7. RichDesmond

    RichDesmond Mu-43 Veteran

    356
    Nov 18, 2011
    Keep in mind that DOF is not an absolute thing. With the high pixel density of modern sensors your actual DOF is less than those markings on lens would have you believe.
     
  8. Hikari

    Hikari Mu-43 All-Pro

    Nov 26, 2010
    DoF is a product of the format, not pixel density. A DoF scale on a lens designed for a 35mm will be off two stops for m4/3 (proportional the the crop factor). So if you set the aperture to f/11, you would use the f/5.6 scale marks.
     
  9. RichDesmond

    RichDesmond Mu-43 Veteran

    356
    Nov 18, 2011
    You're got the right strategy, but for the wrong reasons. :smile: First of all, format has nothing directly to do with DOF. A 50mm lens at f8 has the same DOF regardless of the sensor size sitting behind it. The lens's contribution to DOF is a function of the physical aperture size only.
    Where the format comes in is if you hold FOV constant. Then you would be comparing a 25mm :43: lens to a 50mm lens on a full frame camera, and at the same f-stop the DOF would be different because the physical aperture is different.

    The other thing that impacts DOF is the size of the "Circle of Confusion". Google that for a full explanation. Bottom line though is that modern sensors have much higher angular resolution than 35mm film, a smaller circle of confusion and therefore less DOF.

    On a :43: camera relying on lens markings and the old hyperfocal calculations is guaranteed to get you some blurry photos.
     
  10. Sammyboy

    Sammyboy m43 Pro

    Oct 26, 2010
    Steeler Country
    50% correct, 50% incorrect .... it's all in the lens design in regards to register.
    m43 has a register of 20mm, in this case native lenses conform to your post.

    Using an adapted OM lens having a register of 46mm on m43, the only thing the crop factor effects is the angle of view ...... think about it. :smile:
     
  11. Hikari

    Hikari Mu-43 All-Pro

    Nov 26, 2010
    Actually, I got it all right. DoF is a function of format as each format has a different permissible circle of confusion. A 50mm lens at a given aperture will produce a different DoF on different formats. And the pixel pitch has nothing to do with it, just like using different films with different resolving power did not change DoF.

    If you go back to my original post, it shows how to used the DoF scale on an m4/3 so you can get sharp images. And check the link in the following post.
     
  12. Hikari

    Hikari Mu-43 All-Pro

    Nov 26, 2010
    Flange distance, or lens register if you prefer, has nothing to do with anything except the physical connection. What is important is the optics.

    The crop factor effects the angle of view and the DoF. DoF is always in relation to format as each format has it own permissible circle of confusion. The crop is effectively requiring the image to be magnified to a greater size for a give display size. A circle of confusion that may have been acceptable in a 35mm frame will be enlarged to the point where it is not acceptable.

    Not only have I thought about it, but this type of information I was taught formally and use professionally. :tongue:

    This should explain things for you:

    http://www.zeiss.com/c12567a8003b8b6f/embedtitelintern/cln_35_bokeh_en/$file/cln35_bokeh_en.pdf
     
  13. Sammyboy

    Sammyboy m43 Pro

    Oct 26, 2010
    Steeler Country
    Hikari;211774]
    Flange distance, or lens register if you prefer, has nothing to do with anything except the physical connection.
    Not true, using an adapter of the proper length puts the lens into compliance to its design specifications as to project its designed image circle diameter at the correct distance. In case of OM lenses, that would be 46mm from the lens flange. When mounted on m43, the camera nor the lens knows the sensor size, after all, the projected image is designed to cover the 24 x 36 which is more than required by the m43 sensor. The m43 sensor is recording only a portion of the image, it's not compressing, expanding or changing the DOF. Much like cropping a photograph with a pair of scissors, this certainly doesn't change DOF.

    What is important is the optics.
    Good optics or poor optics doesn't matter, if the lens can not project the image to the design specifications, the quality of the glass proper has little meaning.

    The crop factor effects the angle of view and the DoF. DoF is always in relation to format as each format has it own permissible circle of confusion.
    This is true for native lenses designed for a given format, not the case for adapted lenses from different formats.
     
  14. fin azvandi

    fin azvandi Mu-43 All-Pro

    Mar 12, 2011
    South Bend, IN
    This discussion seems to come up every month or so...suffice it to say I think people are talking past each other or making different assumptions about some of the terms involved. Depth of field is defined in terms certain assumptions about the maximum allowable circle of confusion and a specified print size and viewing distance. When you start comparing the same lens on different sensors without accounting for other factors you run into trouble.

    The best explanation I have found for these concepts is here:
    Depth of Field, Digital Photography and Crop Sensor Cameras - Bob Atkins Photography
     
  15. Lol, yes


    This is correct, but what if that image cropped with scissors is then blown up to the same print size as the original? The only way we can directly compare DOF is to compare images at the same print/viewing size. The smaller m4/3 sensor is not affecting optical properties as the light hits the sensor, but when the image is scaled up for viewing and printing by a larger factor than an image from a full-size sensor, that's where the difference comes from.
     
  16. rich00

    rich00 Mu-43 Veteran

    251
    Dec 8, 2011
    Ok, looks like I triggered a bit of discussion, which is always good as long as it's constructive.

    As per my original post I was curious why the focus scale wasn't used so much on the native lenses. So I looks like I got more information than I needed. Thanks everyone for the responses.

    To the mods please feel free to close the thread.
     
  17. RichDesmond

    RichDesmond Mu-43 Veteran

    356
    Nov 18, 2011
    That's simply not true. The lens's DOF (which is a function of resolution vs. distance) has nothing to do with what the image is projected on. How could it? It just depends on the aperture area.
    Finer grained films DID change the DOF, but the range wasn't that large so everyone just used the 30 micron standard CoC as a "good enough" approximation. Now that we have pixel pitches in the 5 micron range that old 30 micron standard isn't applicable, and if you do a proper DOF calculation that becomes obvious.
    What is true is that smaller formats tend to have smaller pixel pitches, so people often confuse what's really causing the DOF change. But if a :43: camera had the same pixel pitch as a 5D, it would have the same DOF given the same lens FL and aperture
     
  18. Hikari

    Hikari Mu-43 All-Pro

    Nov 26, 2010
    Actually, cropping does change Dof. So does viewing distance. Your example is really not correct as you would crop AND enlarge. As I said, CoC and DoF is a format problem, it has nothing to do with what the lens knows.

    As far as the flange distance, ever 35mm camera manufacturer has a different flange distance and yet the same image circle. So what does flange distance mean except the distance required for mechanical mounting on a particular manufacturer's camera.

    Read the pdf about DoF by Zeiss. It is very basic stuff and covers what happens when you put a lens design for one format put on a smaller format.

    What I meant by optics is that the mechanical flange distance is neither here nor there. What you need is optical distances--12mm focal length is a 12mm focal length no matter how far the lens is physically from the sensor.

    When you mount a lens from a different format on a m4/3, the crop factor from one format to another is also proportional to the change in FoV and DoF.

    Please read the Zeiss document. It will cover all of this quite well. fin azvandi has given a good link as well.

    Did I mention this kind of stuff is to do with my profession?
     
  19. Hikari

    Hikari Mu-43 All-Pro

    Nov 26, 2010
    Actually Rich, it is very true. Sharpness and DoF is a quality that is perceived in a photograph by a viewer--they are purely subjective. If a print looks sharp and has a particular DoF, that will not change if you divide it into more pixels. You are probably getting confused by looking at files at 100% monitor view where you cannot judge DoF. 100% monitor views is not a real world viewing condition and so distorts the view of an image.

    m4/3 will never have the DoF of 35mm or any other format. DoF is really based on format and the corresponding viewing conditions. It does not matter how many pixels a format has.

    Please read the Zeiss document I gave a link to in one of my posts above.
     
  20. Hikari

    Hikari Mu-43 All-Pro

    Nov 26, 2010
    Don't worry about this. This is one of the perennial conversations you are going to have in forums like this. It is just a good thing you did not ask about print size. :rofl: