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Thread: EV, distance to object

  1. #1

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    EV, distance to object

    Good afternoon,

    1. Assuming I want to use EV correction during shooting (no fill flash, bright sunlight), I have set my camera to +0EV according to build-in EV meter, for instance, in Av mode. When EV correction is applied, the camera will override initial settings by EV value. But how will it do that? Will it correct aperture/shutter speed pair to match corrected EV or will it merely apply digital post processing to image brightness leaving aperture/shutter speed the same?

    2. Canon 550D has an ability to measure distance to object. At least, distance to object is stored in the EXIF data. Is there any way to see distance to object camera reading? Having distance to object value on hand, it would be much easier to estimate DoF when shooting from short distances, especially for beginners like me.

    3. Thank you

    Regards,
    Pavel

  2. #2
    Moderator Dave Humphries's Avatar
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    Re: EV, distance to object

    Good afternoon to you Pavel,

    Quote Originally Posted by Destructor View Post
    1. Assuming I want to use EV correction during shooting (no fill flash, bright sunlight), I have set my camera to +0EV according to build-in EV meter, for instance, in Av mode. When EV correction is applied, the camera will override initial settings by EV value. But how will it do that? Will it correct aperture/shutter speed pair to match corrected EV or will it merely apply digital post processing to image brightness leaving aperture/shutter speed the same?
    If you ask it for an Exposure Compensation (I know it as EC, but that maybe Nikon terminology), say minus 1 stop, and you are in aperture priority mode, the camera will increase the shutter speed by one stop there and then. It immediately affects the exposure and is not something applied in PP (although it is recorded in the EXIF data).

    If you ask for minus one stop EC in Shutter priority (Tv), it will stop the lens down one more stop.

    If, in trying to apply the correction, it runs out of aperture range (lets say it cannot open up enough, then I don't know what it would do, probably depends on the camera model, I can only suggest reading the manual or trying it out.

    If you are in (P) program mode, there might be a menu setting which determines what it does, but as a guess I would bet that it'll work the same as aperture priority and affect the shutter speed, because you are far less likely to run out of available shutter speeds.

    In (M) Manual mode it doesn't work because you have control of all adjustments anyway (it may bizarrely still be logged in the EXIF data though - it ought to be blank or zero in M mode).

    Quote Originally Posted by Destructor View Post
    2. Canon 550D has an ability to measure distance to object. At least, distance to object is stored in the EXIF data. Is there any way to see distance to object camera reading? Having distance to object value on hand, it would be much easier to estimate DoF when shooting from short distances, especially for beginners like me.
    That's a very good question; it would be useful to know at the time, wouldn't it?

    Personally, I bet it isn't half as accurate as they make out (mine said "6.31m" recently) and if you had access at the time, "every man and his dog" would be getting out a tape measure and then sending their lenses back to have it recalibrated. Still, it wouldn't hurt to have a rounded down version available, say accurate to 10cm or so.

    Great idea though.

    Cheers,
    Last edited by Dave Humphries; 2nd April 2012 at 09:59 PM. Reason: fix error

  3. #3

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    Re: EV, distance to object

    Dave,

    Thank you for the input. I do appreciate your help. I was definitely talking about EC. Sorry for typo.

    Regards,
    Pavel

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    William W's Avatar
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    Re: EV, distance to object

    ANSWER 1.
    Exposure compensation works in Av, Tv, P and A-DEP Modes

    In Av Mode the Exposure Compensation is applied by changing the SHUTTER SPEED.
    If the EC is negative / minus / - : the SHUTTER SPEED will be INCREASED , i.e. a FASTER shutter speed will be activated commensurate with the EC selected.
    If the EC is positive / plus / + : the SHUTTER SPEED will be DECREASED, i.e. a SLOWER shutter speed will be activated commensurate with the EC selected.

    In Tv Mode the Exposure Compensation is applied by changing the APERTURE.
    If the EC is negative / minus / - : the APERTURE will be DECREASED, i.e. a SMALLER aperture (larger F/number) will be activated commensurate with the EC selected.
    If the positive / plus / + : the APERTURE will be INCREASED, i.e. a LARGER aperture (smaller F/number) will be activated commensurate with the EC selected.

    In P Mode the Exposure Compensation is applied according to the P Mode Algorithm which tends to bias Shutter Speed to allow Hand Holding BUT the EC compensation will be applied to EITHER the Shutter Speed or the Aperture, depending upon the lens and the lighting situation.
    In any event, PROGRAM SHIFT can be applied after EC is applied, such that a suitable user controlled Aperture and Shutter Speed might be selected.

    Exposure Compensation used when in A-DEP MODE, should function as per P MODE, but I haven’t used this combination.

    If (for example in Tv Mode) the EC is set such that the lens runs out of available APERTURE to make the necessary correction, the aperture will BLINK. The same will apply if the camera runs out of available Shutter Speed when EC is used in Av Mode.

    It is unlikely that the camera and lens will run out of available Tv and Av when in P Mode shooting any scene at any ISO – except save for shooting directly into the sun at max ISO, and selecting maximum negative EC – and that would be just . . . silly.

    ANSWER 2.
    No, you cannot see the distance info as a display in the camera.
    BUT – what is (are) your difficulty (ies), specifically, with managing / estimating DoF?




    WW
    Last edited by William W; 2nd April 2012 at 10:39 PM. Reason: Removed my postscript mentioning an error in another post, which has now been corrected

  5. #5
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    Re: EV, distance to object

    Some lenses have a distance scale which will give you an approximation of the distance at which you are focused.

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    Re: EV, distance to object

    Bill,

    Thank you for the input. I have made a couple of portraits using EF-S 55-250 F/4-5.6 IS. Shooting details are: F/4.0, focal length - 55.0mm, approximate distance to object - 2.5 to 3.0 meters. A DoF calculator estimates DoF to be within 30-40cm, what is quite narrow. A father was holding a child. My idea was to blur background and to make a father and a child sharp enough. Shooting from short distances is really a problem for me since I cannot estimate distance to object precisely enough. Moreover, I do not know how. The only way I see to do that is varying aperture and making a number of trial shots. If there is an easier way I would be thankful if you shared your experience.

    P.S. Sorry for my English. Hopefully, I have clearly described the problem.

    Regards,
    Pavel

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    William W's Avatar
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    Re: EV, distance to object

    Quote Originally Posted by Destructor View Post
    I have made a couple of portraits using EF-S 55-250 F/4-5.6 IS. . . . If there is an easier way I would be thankful if you shared your experience.

    There certainly is a much easier method.
    Especially for Portraiture - you do NOT need to know the SD (Shooting Distance) to accurately compute the DoF which will be available to you.

    DoF is directly related to “The Shot”. (“The Shot” in Portraiture, is seen as the “Framing within the Viewfinder”)

    The DoF will be CONSISTENT any one SHOT within any one camera FORMAT.
    This fact is based upon the Axiom of Depth of Field.

    Typically, there are three basic Shots, in Portraiture.
    These are:
    1. The Head Shot
    2. The Half Shot
    3. The Full Length Shot

    I memorized the DoF for only three apertures each for those three shots for both for Horizontal Framing and also for Vertical Framing.

    As my initial memory aid, I made cheat cards for each of my camera formats.

    If you choose to use this method, you could make your own Cheat Cards specific for APS-C format camera.
    I suggest that you round-off the numbers, conservatively, such that they underestimate the DoF and also so they fall into a number pattern, which is easy to remember.

    I find this method very easy to apply to intermediate shots and / or to intermediate apertures:
    For example, if I were using my 5D and taking an Half Shot, in Vertical Framing and the circumstances required me to use F/8 - I know that the DoF would be 18”

    Here is an example of one of the two cheat cards I made a long time ago, for my 135 format cameras (AKA “Full Frame”) - I used imperial measure a long time ago:

    EV, distance to object

    Also having this knowledge and the application of some assumption of average sizes using this method allows it to be applied in many other circumstances: knowing average human dimensions allows a quick practical application for judging accurately the DoF required for group shots and or photographing inanimate objects . . . the applications are as endless as your requirements . . . etc.

    WW

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    Moderator Dave Humphries's Avatar
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    Re: EV, distance to object

    Quote Originally Posted by William W View Post
    I believe this is either an unintentional slip-up or a poor choice of words: the shutter speed will be made faster (i.e. increased), not slowed.
    Unintentional slip up corrected

    Thanks Bill, sorry Pavel; I'm supposed to help!

    Cheers,

  9. #9
    William W's Avatar
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    Re: EV, distance to object

    ^^^ Dave – Pls. see my amended post #4.
    I have my subsequently removed PS for better continuity of the final thread and to make it easier for you to tidy up by deleting all references, including this post, if you so choose.
    Rgds,
    Bill

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    Re: EV, distance to object

    Bill,

    WOW! Good and simple approach for estimating DoF. I really like cheat cards and will prepare my own or will simply memorize required figures. Let us assume I am shooting the full length portrait and a human silhouette is approximately 8ft (2.4m). Let us assume I am using my EF-S 55-250 zoom lens. Obviously, there are a number of ways to get 8ft (2.4m) silhouette in a viewfinder:

    a) I can step further from object and zoom in till a silhouette fills the frame
    b) I can step closer to object and zoom out till a silhouette fills the frame

    Will DoF be the same for the a) and b) cases? Will front/back DoF distribution be the same for the cases above? Thank you.

    Regards,
    Pavel

  11. #11
    jprzybyla's Avatar
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    Re: EV, distance to object

    I use the Preview button on my Nikon to see the depth of field. Works for me when I want to see what is in focus and what is out of focus.

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    Re: EV, distance to object

    Joe,

    LCD resolution is not high enough to see if a human's eyes and ears are in focus (even zoomed in completely). An image might seem sharp at LCD while post processing will reveal what is in focus and what is not. If an image looks shaprt at LCD it means for me next to nothing. Unfortunately, this is quite rough estimation. Thank you for the input anyway

    Regards,
    Pavel

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    Re: EV, distance to object

    Quote Originally Posted by Destructor View Post
    Joe,

    LCD resolution is not high enough to see if a human's eyes and ears are in focus (even zoomed in completely). An image might seem sharp at LCD while post processing will reveal what is in focus and what is not. If an image looks shaprt at LCD it means for me next to nothing. Unfortunately, this is quite rough estimation. Thank you for the input anyway

    Regards,
    Pavel
    I suspect that Joe is referring to the DOF preview button and looking at the image through the viewfinder, rather than using the LCD screen. That being said, it is only a guide as well as the view is not necessarily great when the lens stops down.

    I've always found that the real "secret" to portraiture is to focus on the eye nearest the camera, and that will usually give you a good, useable shot. Don't forget that DOF is not equally distributed; for a given f/stop the DOF extends 1/3 in to the front of the focal plane, but 2/3 to the rear. If you focus on the nearest eye, usually the nose will be in focus, as will the ears, even when shooting wide open. The only time I've had problems with this is when shooting wide open with a very long lens (400mm lens), I have had some shots where the eye is in focus, but the tip of the nose is not.

    If you are shooting 2 people, focus on the eye of the person in front. Even if the person in the background is not 100% in focus, the image is more esthetically pleasing than having the person in front out of focus.

  14. #14

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    Re: EV, distance to object

    Quote Originally Posted by jprzybyla View Post
    I use the Preview button on my Nikon to see the depth of field.
    Having external flash installed, DoF check button activates modeling flash, instead of checking DoF. Unfortunately

    Regards,
    Pavel

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    Re: EV, distance to object

    Quote Originally Posted by Destructor View Post
    Let us assume I am shooting the full length portrait and a human silhouette is approximately 8ft (2.4m). Let us assume I am using my EF-S 55-250 zoom lens. Obviously, there are a number of ways to get 8ft (2.4m) silhouette in a viewfinder:
    a) I can step further from object and zoom in till a silhouette fills the frame
    b) I can step closer to object and zoom out till a silhouette fills the frame
    Will DoF be the same for the a) and b) cases?
    Will front/back DoF distribution be the same for the cases above?
    For clarity -

    The 8ft in my diagram represents the Field of View AT the Plane of Sharp focus.
    In other words, I am at sharp focus on a 6ft person standing up and I have framed the shot with 1ft above his head and beneath his feet.

    ***

    Simple answers to your two questions, for all practical purposes and for use in the field:

    YES the DoF is the same.

    YES, the distribution will be the same ratio in front and behind the Plane of Sharp Focus provided the SHOT is the same TYPE of shot – i.e. whether it is a TIGHT SHOT or a LONG SHOT.

    ***

    The detail is in the mathematics and simply put:

    A. The answer “YES” - the DoF will remain the same:

    1. The Axiom of DoF indicates that the DoF will always be the same for any one camera format for any aperture provided the FRAMING is the same. This axiom will hold true for all practical purposes.

    In the detail of the mathematics, we can disprove the Axiom for some situations (and that is why it is an Axiom and not a Theorem).

    2. The Axiom becomes less valid when we use very wide lenses and get very close to the Subject.

    But it is not often that we take a Tight Head with a Super Wide Lens (this would be akin to CLOSE UP work). But even if we do use a Wide Lens at close Subject Distance, for a Portrait Shot, the difference of the DoF is only very minor – it is just slightly more.

    3. The Axiom is not true for MACRO work.

    One easy to remember example which I use at workshops is 50mm Lens and the Half Shot, using a CoC of 25Microns (Full Frame Camera):

    As per my cheat card the DoF is 2ft – the same if we use a 100mm Lens or a 400mm Lens the DoF will still be 2ft.

    For a 50mm lens we are at 5’6” Subject Distance (SD);
    for a 100mm lens we are at 11ft SD;
    and for a 400mm lens we are at 44ft SD.

    (If we use a 25mm Lens and make the shot at SD = 2’9”, the DoF is still (about) 2ft, but it is actually a tad more - about 2⅞” more.)

    ***

    B. The answer “YES”, the distribution will be the same ratio in front and behind the Plane of Sharp Focus.

    The RATIO of the Spread of DoF will be DEPENDENT upon whether it is a TIGHT SHOT or a LONG SHOT.

    (Tight Shots are also referred to as “Close Shots”)

    (Long Shots are also referred to as “Wide Shots”, which often makes for more confusion with lens’s focal lengths)

    When we are considering LONG SHOTS - the ratio of the SPREAD of the DoF with VARY with the APERTURE USED.

    For LONG SHOTS you must consider that the larger the APERTURE used, the greater the ratio of the DoF biased toward BEHIND the Plane of Sharp Focus.


    More Definitions of "The Shot":

    “TIGHT SHOT” and a “LONG SHOT” do NOT have any relationship to the LENS’s FOCAL LENGTH – the terms loosely describe the MAIN SUBJECT and how that subject is portrayed, in the scene.

    For example – BOTH these images are made with a 50mm lens on an EOS 5D -

    This is a TIGHT Shot with a 50mm lens:
    EV, distance to object

    This is a LONG Shot with a 50mm lens:
    EV, distance to object



    Examples of different types of Shots, using different Focal Legnths -
    This is TIGHT Shot, (or Close Shot “of the Girl”) made with a 24mm lens:
    EV, distance to object


    And this is a LONG Shot, (or WIDE Shot – “of the group”), made with a 400mm lens:
    EV, distance to object

    ***

    Explanation of: “The ratio front and behind will be a DIFFERENT RATIO, depending upon the TYPE of SHOT.”

    This is where many Photographers become unstuck, especially when shooting Portraiture, because they believe that the ⅓ in Front and ⅔ Behind Rule is a Rule of Thumb for all circumstances – IT IS NOT.

    It is better to think generally of TWO Rules of Thumb.

    The ⅓ Front and ⅔ Behind Rule, for LONG SHOTS. (example Group Portraits)

    And it is better to use the ½ and ½ Rule for TIGHT SHOTS. (example Half Shot Single Portrait or Head Shot)



    ***

    Practical Examples:

    For any TIGHT Shot, for example a Head shot or an Half Shot Portrait, it is better to use the ½ and ½ Rule as a guide for the distribution of Dof.

    For an example: this a Half Shot at 45° Profile:
    EV, distance to object
    Candid Portrait # 504468v06
    (5D+85 F1.8 @ 1/80s @ ISO400 HH Manual)

    The SD is about 8ft and the DoF is about 3”.
    The distribution of DoF is – 7’10½” to 8’ 1½”
    this is a 1:1 ratio - The ½ and ½ DoF Rule of Thumb.

    Focus was made on the Rim Light edge - of the Bridge of the Nose – knowing that this was 45° Profile (eyes will be at the same distance front and back of the nose) and for a Tight Shot it is best to use the ½ and ½ Rule . . . the Photographer focussed on the bridge of the nose to ensure that both eyes are captured in acceptable focus, even when using a very shallow DoF.

    ***

    Use the ⅓ Front and ⅔ Behind Rule for a LONG SHot eg - A GROUP PORTRAIT with two or three rows of people.

    Good advice is to use the ⅓ Front and ⅔ Behind Rule but only AS A GUIDE – for example, to make focus on the second row, if there five rows.


    About the APERTURE USED for LONG SHOTS and the CHANGE of the DoF Distribution

    Using the ⅓ Front and ⅔ Behind Rule can be a trap when using the smaller apertures for Long Shots (for example Group Portraits).

    I would advise caution and advise you get an understanding of how, the BEHIND area of the DoF INCREASES as the aperture becomes smaller.

    Let’s look at a the same Group Portrait – which is a typically a LONG(er) shot:
    EV, distance to object

    If the Photographer used F/5.6 for this Group Portrait, and the SD was 25’, the resultant DoF would be about 17’6” to 43’ – that is a ratio spread of about 1:2
    This concurs with the ⅓ Front and ⅔ Behind Rule.


    BUT - this is the trap many fall into:
    Let’s move the aperture to F/11 for the same shot.
    Certainly the DoF will increase.

    But at F/11 for that shot, the distributed of the DoF is in a ratio of about 1/12th in Front and 11/12ths Behind.

    So beware - and note that there is NOT MUCH gain IN FRONT of the Plane of Sharp Focus as you stop down to increase the DoF when you are making the Longer Shots.

    WW
    Last edited by William W; 4th April 2012 at 02:50 AM.

  16. #16

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    Re: EV, distance to object

    Bill,

    I appreciate your time you spent explaining me rules of thumb. Thank you.

    Regards,
    Pavel
    Last edited by Destructor; 4th April 2012 at 06:33 AM.

  17. #17
    Photon Hacker's Avatar
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    Re: EV, distance to object

    Quote Originally Posted by GrumpyDiver View Post
    Don't forget that DOF is not equally distributed; for a given f/stop the DOF extends 1/3 in to the front of the focal plane, but 2/3 to the rear.
    Is this a theorem or a thumb rule?.

  18. #18

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    Re: EV, distance to object

    Mario,

    Statements above are the set of general practical rules that work (i.e. rule of thumb). In general, too precise DoF computing is not necessary in practice. The approach described by Bill simplifies complicated theory, where distance to object is replaced by frame size (logically, there is dependence between these two figures). Distance to object can hardly be estimated (no problem if you carry laser meter with you of course ) Again, this is approximation. In my opinion this is quite good practical one.

    Feel free to ask more if my words sound mysteriously.

    Regards,
    Pavel

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    William W's Avatar
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    Re: EV, distance to object

    Quote Originally Posted by Destructor View Post
    ]Statements above are the set of general practical rules that work (i.e. rule of thumb).

    The approach described [using the Axiom of DoF] simplifies complicated theory, where distance to object is replaced by frame size (logically, there is dependence between these two figures).


    Just to be clear:

    The Axiom, or using FRAMING to reckon the DoF consistently for mostly all shooting distances, is much stronger; more accurate; and more reliable than any Rule of Thumb.
    This is so because of the mathematical formulae which determine DoF and within those formulae, the mathematical relationships between the Field of View and the Depth of Field.

    Rules of Thumb, for example, describing how much in front and how much behind are much less consistent and much less reliable.
    Again, this because of the mathematics involved and the mathematical relationship of Shooting Distance to the distance to the Front and Rear planes of DoF.

    WW

    (Mentioned only to attain clarity about the strength of the method - do not misinterpret this as correcting you or being pedantic).

  20. #20

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    Re: EV, distance to object

    Quote Originally Posted by Destructor View Post
    Good afternoon,

    1. Assuming I want to use EV correction during shooting (no fill flash, bright sunlight), I have set my camera to +0EV according to build-in EV meter, for instance, in Av mode. When EV correction is applied, the camera will override initial settings by EV value. But how will it do that? Will it correct aperture/shutter speed pair to match corrected EV or will it merely apply digital post processing to image brightness leaving aperture/shutter speed the same?
    The only thing that EC does is bias the meter. So if the meter is telling the rest of the camera that the lighting is 14 EV, and you set EC to +1, then the meter will report 13 EV to the camera (the EC value you set is subtracted from the meter reading.) The camera will then perform as it normally would with that level of light. So there's no difference in camera performance between a light level of 13 EV, and a light level of 14 EV with +1 EC.

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