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Thread: How to use the depth of focus markings

  1. #1
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    How to use the depth of focus markings

    Hi
    I would like to understand how to use the dof markings on my new lens.
    It is a Canon 135mm and has two f32 dof markings under the distance markings.
    I would love it if someone could explain to me in simple terms how to use this.
    Thanks so much
    Lesley

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    jiro's Avatar
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    Re: How to use the depth of focus markings

    The distance marking (either in meters or in feet) on your lens IN BETWEEN the f-stop you are using is the depth distance that is IN FOCUS for that f-stop.

    Example: If I use f/22 on my 50mm lens and the center marked line is located at 2 feet, the image distance depth in focus is approximately FROM 1.8 feet UP TO 2.3 feet.

    There is a tutorial with respect to Depth of Field here at CiC. I suggest you read this as this is a more comprehensive explanation regarding f-stop and depth of field. http://www.cambridgeincolour.com/tut...h-of-field.htm
    Last edited by jiro; 10th February 2011 at 08:55 PM.

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    Re: How to use the depth of focus markings

    Quote Originally Posted by LesleyBray View Post
    Hi
    I would like to understand how to use the dof markings on my new lens.
    It is a Canon 135mm and has two f32 dof markings under the distance markings.
    I would love it if someone could explain to me in simple terms how to use this.
    Thanks so much
    Lesley
    The short answer: On that lens, the two "F/32" markings, are not much practical use at all.

    If you turn the Focus Turret of the lens from ∞ to 0.9m the compass is only about 90°, which means the Distance Scale is quite squashed, hence the resultant DoF scale is also squashed.

    It is not any requirement that the lens has Distance and Aperture markings on the lens’s focus turret. These markings are merely an indicative and not an accurate measure in any case. But they did (do) serve some purpose, if there are enough of them, and the Aperture Markings indicate useful (often used) Apertures.

    The two main purposes the Aperture Marks serve are:

     Hyperfocal Distance Focus Technique
     Zone Focus Technique (and A Visual Scale, to the Depth of Field)

    Hyperfocal Distance Focus Technique
    With older lenses for example my Rokkor 50mm F/1.2, here:


    How to use the depth of focus markings



    The lens’s Turret is labeled with many F/stop numbers either side of the Focus mark.

    Note the lens is focused on "∞" and either side of the Focus Line indicating the lens is focused on infinity are the numbers: 4; 8; 16.

    There is a bar between 8 & 16 and that indicates F/11.

    Notice that on the left hand side, the F/8 mark aligns with 10m or 30ft, and so when the lens is focused at infinity you can expect that everything will be in “about” acceptable focus from 10m to infinity, when using F/8.

    However, should we move the Focus Turret such that the infinity symbol is level with the other F/8 indicator, the lens would be focused at about 10m and the each of the two F/8 indicators would read “5m” and “∞”, respectively.

    [NOTE: the Hyper Focal Distance using F/8 for a 50mm lens used on a 135 format (aka "Full Frame") is 12.55mtrs, when setting CoC to 0.025mm ]

    So, the procedure for setting the lens to the Hyper Focal distance using the lens indicators is:

    1. Choose the aperture you wish to use.
    2. Set infinity (∞) focus to that aperture mark.
    3. Compose.
    4. Shoot.


    ***


    But on my Canon EF 50mm F/1.4 the Focus Turret is labeled like this:

    How to use the depth of focus markings


    (Just like the EF135/2 in question - only ONE set of Aperture DoF indicators)

    Note that there is not much space between the 3m indicator and the infinity indicator and just having the one F/22 indicator is as useful as teats on a bull, for any guide whatsoever.
    The method of using the lens’s Focus Turret and Distance Markings aligned with the Aperture Markings for setting a rough (but reasonable accurate) Hyper Focal focus distance - is usually quite impossible with mostly all modern lenses.

    ***

    Zone Focus Technique (and a visual scale indicating DoF)

    Again, referring to the Rokkor 50/1.4 lens.

    Imagine we were shooting a Door Stop, “Hail Mary” style and the subject was about 15 ft away and moving toward us.

    Setting the 15ft mark on the RH Aperture “F/8” the LH “F/8” would align just short of the 10 ft mark on the distance scale – thus allowing us to zone focus about 9ft to 15 ft.

    Rule of thumb: ⅓ in front ⅔ behind, therefore we are at sharp focus at about 11ft (2ft after 9ft, 4ft before 15ft.

    Keep about 11ft from the Subject as he exits the media scrum and shoot away at Aperture = F/8.

    (Liberties taken for choosing “F/8 and be there” but I remember the Main Focus Zones for F/8, by rote.)

    ***

    With AF Lenses, there’s not much use for Zone Focus in that situation any more, but knowing the Zones and the Technique (although a dying skill) is still useful.

    Zone Focus for the Processional, at a Wedding, is one example.

    Also Zone Focus (at least knowing the zones for an aperture) is sometimes useful to combine with Manual Flash Fill at a Wedding - especially if the B&G are on the move - such as the Recessional or First Dance.

    This is a recent occasion where I used an [#1]adaption of Zone Focus Technique, as I was moving sideways and parallel to the Plane of Sharp Focus, to avoid the intruder coming from camera Right:

    How to use the depth of focus markings
    Tech: 5D 50/1.4
    Shooting: as indicated, Hand Held, Available Light



    [#1] (i.e. an “Adaptation of Zone Focus Technique” because I just know the DoF at specific Apertures on a 5D, I did not “read the DoF” from the Distance Scale on the Lens)


    WW

    PS - FYI, Your header is in error - "Depth of Field" is different to "Depth of Focus" - both are related, but they are different.

    We are discussing Depth of Field here.
    Last edited by William W; 11th February 2011 at 09:13 AM. Reason: spellllllllling misssssstakes

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    Re: How to use the depth of focus markings

    Thank you Jiro and Willia for your explanations
    William I have read your response a couple of times very carefully and now find I understand the Hyperfocal Distance Focus Technique - I wish lens were still marked like this. Now I am off to study your Zone focus - I think it is going to take a little while to sink in.
    Once again - many thanks.
    Lesley

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    Re: How to use the depth of focus markings

    Quote Originally Posted by LesleyBray View Post
    . . .I have read your response a couple of times very carefully and now find I understand the Hyperfocal Distance Focus Technique - I wish lens were still marked like this. Now I am off to study your Zone focus - I think it is going to take a little while to sink in.

    Using Zone Focus Technique, once the Zone of Focus is established - the two most common basic applications are:

    a) the Photographer keeps the same distance from the subject (i.e. moves with them)

    b) the zone is designated in the Photographer’s mind (e.g. between That far Pew and This close Pew) and a shot or shots are taken, as the Subject moves through the Zone.

    The Zone Focus Technique is different to using a Pre Focus Point.

    When using a Pre Focus Point, the shutter is released when the subject is at that point (e.g. a dog jumping over an hurdle in a park); and the focus is set at the hurdle and the shutter is released as the Dog jumps over it.

    The difference between these two techniques and the choice of which one is used, is often predicated by the fact that with Zone Focus, the Photographer is waiting for the attitude of the Subject to be suitable, before the Shutter is released, so either the Photographer keeps moving to keep the Subjects in the Zone of Focus, or alternatively the Zone of Focus is large enough for the Photographer to have a lot of choices, as to when to release the Shutter.

    In the example of the two women above, the women were not moving – but when I moved to my left, I was avoiding the intruder who was about to block my view. When I moved I attempted to move in an arc to keep the Zone of Focus on the two women.

    Obviously that shot had a time constraint on it, because I started with the two women standing in the same Plane, but as I moved, the scene changed such that one woman began to be behind the other.

    With the Photo of the two Women, I did not use the Markings on the lens’ turret to establish the Zone of Focus, (as we discussed above), but I know that if I use F/2.8 to F/4, when making a Vertical Full Length Shot using my 5D - I have as a minimum of about 2ft DoF.

    So I used Centre Point AF on the Bust Line of the Black Dress; Locked Focus; and then proceeded to stay at a Shooting Distance, so the women remained in that Zone of Focus.

    The example Photo of the two Women is, as I wrote, just “an application” of Zone Focus – and not a typical example.

    This all happened very quickly: As the intruder began to move across my line of sight, I had already committed to having Locked AF, so I continued instinctively on that path, because of my experiences.

    Another method for that shot, would have been to move quickly to get ouit of the way of the intruder and refocus using AF on the line of the Black Dress; Lock Focus; Recompose; Shoot.

    By posting that image, I am not suggesting one Technique is better than the other, but just giving an example of the technique and when I (instinctively) dragged it up from the past to use recently.

    Also please note these are not "my" Techniques. These are practical skills taught at Technical College (NOT TAFE) by Teachers who were qualified in the Craft (Technical Skill) of Photography. These Skills and also the Theory were all examinable subjects and part of the Course.

    WW

    PS the EF135 F/2L USM, is magic - enjoy it.

  6. #6
    inkista's Avatar
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    Re: How to use the depth of focus markings

    Errr... isn't using the DoF scale marks to set hyperfocal distance only accurate for full-frame?

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    Re: How to use the depth of focus markings

    Quote Originally Posted by inkista View Post
    Errr... isn't using the DoF scale marks to set hyperfocal distance only accurate for full-frame?
    Yep Kathy I agree 100% correct.
    But that too, just like the very few markings on modern lenses, is not really of any practical relevance, in the field.

    ***

    With those lenses I used as examples yes - those markings are for 135 format cameras.

    However, The Margin for Error is quite large anyway – i.e. actually lining up the Aperture markings with the Distance Numbers is pretty much a “shot in the dark”.

    For example:

    1. The Hyperfocal Distance at F/8 for a 50mm lens on a 135 format camera is around 40ft.
    2. The Hyperfocal Distance at F/8 for a 50mm lens on an APS-C is about 60ft.


    Referring back to the Rokkor 50mm lens and pretending we mount it on my 30D and my 5D:


    If we set the “∞” mark to “8” it would only be a small touch of the Focus Turret for the lens to be actually focussed at 40ft or 60ft or somewhere in between, as you can see there is not much space between the 30ft indicator and the infinity indicator.

    WW

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    inkista's Avatar
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    Re: How to use the depth of focus markings

    Ah. gotcha. Too bogged down in theory to pay attention to practice.

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    William W's Avatar
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    Re: How to use the depth of focus markings

    . . . for Hyperfocal Distance Focusing Technique on that 28/2.8 where the lens's focusing turret has a large compass from minimum focus to infinity, which we are discussing here: Best Prime Lens , you might find more, but still only a small significant difference to note and maybe you might need to adjust for the differences when using the lens on an APS-C.

    This will be more noticeable if using F/16 or F/22.

    But even for that lens, the Distance Numbers get very squashed, at the infinity end - it is the nature of the focusing mechanism.

    WW

  10. #10

    Re: How to use the depth of focus markings

    Quote Originally Posted by inkista View Post
    Errr... isn't using the DoF scale marks to set hyperfocal distance only accurate for full-frame?
    I usually find Canon's DoF markings and tables a bit optomistic.....I think they're for a 10x8 inch print from full frame. No good for pixel peepers with macro lenses

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