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Thread: Dof/point of focus

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    Dof/point of focus

    Hi everyone,

    I'm a Nikon user and have a problem with Point of Focus and Depth of Field/Hyperfocal Distance.

    Ouch!!!!!

    I have to take an indoor picture of a 3 rows of 6 tables with 18 diners sitting each side of the leg. Each row of tables (legs) measure some 12 mtrs long. The legs are not Horizontal to the camera but verticle/ going away from the camera position and I will be perched up on a stage to look down on the diners.

    The legs begin some 5 mtrs from the camera position and then extends for approx 12mtrs

    I have looked at DOF sites and still not sure where to pickup the point of focus for maximum depth of field.

    I have enough power to light the whole scene with an aperture of f11/13 with a 28-70mm nikon f2.8 lens and I have to us ISO800 to achieve f11/13. I'll be shooting with a Nikon D700 FX.

    So, I hope members might be able to suggest where to pickup the point of focus to ensure the best Depth of Field.

    Thanks for reading my thread.
    Last edited by shareindex; 24th November 2012 at 05:14 PM.

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    Re: Dof/point of focus

    To be completely accurate, you might need to provide the focal length you will use. There are a lot of Depth of Field calculators and charts on the Internet that would provide the information you are seeking.

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    Re: Dof/point of focus

    Hi Nikon user,

    Do you have a first name? (we much prefer them)

    You may find this tutorial helpful; http://www.cambridgeincolour.com/tut...h-of-field.htm

    A 12m DoF is required.

    The split will be something like 47%/53% (fore/aft) at the sort of focal length you'll probably be using, so in very round figures, about 11m into the shot (5m + 12/2m) would be where to focus, just shy of half way down the table.

    You don't say what your camera body is (i.e. FF or DX), which is really helpful to use a DoF calculator.

    However dialling a few figures into that shows DoF shouldn't be too much of a problem at f/11 and an 11m focus distance as long as you stay fairly wide angle.

    Welcome to the CiC forums from ....
    Last edited by Dave Humphries; 24th November 2012 at 05:08 PM. Reason: corrected errors

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    Re: Dof/point of focus

    You need to provide other information (as already mentioned).
    The most pressing information required is the WIDTH of the scene and also the Camera FORMAT.
    The PURPOSE / USAGE of the final product would also be handy as would the ELEVATION of the Camera.

    However – making a few logical assumptions – I see the shooting scenario thus:
    Dof/point of focus

    IF CORRECT - it occurs to me that you will need to shoot in PORTRAIT ORIENTATION.

    You will NEED a FX Camera, because 28mm is NOT going to be WIDE enough on a DX (APS-C) Format camera to get 12 mtrs in frame shooting at about 5mtrs from one end.

    You will have plenty of DoF at those Apertures you describe – PROVIDED that the end use is NOT an enlargement to be scrutinized at Gallery Viewing Distances.

    Focussing a tad closer to you than the middle of the tables will suffice – that will be at about 9~10mtrs FROM THE CAMERA.

    Use about FL = 30mm.

    Make a test shot if you can get into the venue – just use markers at the outline four corners of wher the tables will be.

    IF these assumptions are not correct – or not close to correct - then you really do need to provide more details.


    Dof/point of focus

    12mtr tables 5mtrs from dias – 30mm lens – FX Camera – Portrait Orientation:

    Focus @ 11mtrs: DoF = 2.4mtrs to ∞

    Focus @ 9mtrs: DoF = 2.4mtrs to ∞

    WW
    Last edited by William W; 24th November 2012 at 01:33 AM. Reason: corrected a spelling mistake

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    Re: Dof/point of focus

    Quote Originally Posted by shareindex View Post
    I have to take an indoor picture of a row of 6 tables with 18 diners sitting each side of the leg.

    The entire leg measuers some 12 mtrs long. The leg is not Horizontal to the camera but verticle/ going away from the camera position and I will be perched up on a stage to look down on the diners.

    The leg begins some 5 mtrs from the camera position and then extends for approx 12mtrs
    Hi, having read your description and then Dave's reply I'm unclear of the 'actual' length thats required to be in focus. You say the 18 diners will be sat each side of the leg (I assume this is the table), then in the next sentence mention the leg measures some 12 mtrs long.

    I have read this as the leg (table) is 12 mtrs long and assume any calculation is looking for at least a 12 mtr DOF so both those in front and at the rear are in focus ? Dave has mentioned a 7 mtr DOF, I am of course not saying he's wrong but raising this as it may be relavant.

    Grahame

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    Re: Dof/point of focus

    Whilst watching the rain pour down when I have work to do outside I delved deeper into this one as I have also undertaken some 'function' work recently as a favour which was totally new to me and I like to learn.

    Using DOFMaster with calcs based on a DX sensor (D300) , using a FL of 30mm and making further 'assumptions' from your description I came up with the below. Appologies if I have assumed your height wrong but I used 1.8 mtrs but it will make no difference.

    Dof/point of focus

    From what I can determine based on the 'assumptions' you are fine to focus anywhere between the closest and mid person along the table length and be safe.

    In addition to the DOF aspect I looked to see (based on the same assumptions) whether the FOV (field of view) if using a DX crop sensor in portrait orientation would be ok. The FOV for a 1.5 crop sensor size 23.6 x 15.8mm is 29.5 degrees and the sketch below shows that at the assumed shooting distance at FL 30mm you will be able to cover a subject width of 2.99 mtrs where the closet people are.

    Dof/point of focus
    Last edited by Stagecoach; 24th November 2012 at 09:24 AM. Reason: Added FOV data for the same assumption

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    Re: Dof/point of focus

    I wrote:
    Quote Originally Posted by Stagecoach View Post
    . . . You will NEED a FX Camera, because 28mm is NOT going to be WIDE enough on a DX (APS-C) Format camera to get 12 mtrs in frame shooting at about 5mtrs from one end.
    I retract that statement as it is technically incorrect.

    I replace it with:
    “It would be MUCH EASIER to use an FX camera, but it is possible though probably not useful to make the shot with a DX Camera”

    Using a DX Sensor camera and a 30mm lens, at SD (Focus Distance) = 11.105m; the FoV will be approximately 9m x 6m – so whilst the Focus Point should be at about 9~11mtrs, the shot would need t be RECOMPOSED such that the middle of the frame were higher, near the end of the table, such that the FoV would be about 13mtrs along that edge.

    HOWEVER, even though this Focus and Recompose would allow about 13mtrs along the longer edge, and allow an ‘acceptable’ DoF - the point of Closest Acceptable Focus will be at about 4mtrs from the Camera.

    CONSIDERING the people will be sitting upright at the tables, it is very likely that those closest people will have UNacceptable fuzzy heads – and that’s why I wrote that an FX camera is required for the shot – (based on reasonable assumptions and pending exact data from the OP).

    I appreciate the added (FoV) information recently added by Grahame.

    Notwithstanding this information and his assumed arrangement of the tables, I believe my assumption of heads being fuzzy is still correct.

    All these assumptions will be cleared by more exact data, OP, please.

    WW

    (Aside) – Bravo Grahame – excellent diagrams: very much appreciated.
    Last edited by William W; 24th November 2012 at 10:05 AM.

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    Re: Dof/point of focus

    Quote Originally Posted by Mike Buckley View Post
    To be completely accurate, you might need to provide the focal length you will use. There are a lot of Depth of Field calculators and charts on the Internet that would provide the information you are seeking.
    Hello Mike,
    Yeh, I'll be using the lens wide at 28mm because there are 3 legs side by side leading away from the camera position with a top table spanning the entire 3 legs at the top of the legs.

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    Re: Dof/point of focus

    Quote Originally Posted by Stagecoach View Post
    Dave has mentioned a 7 mtr DOF, I am of course not saying he's wrong but raising this as it may be relavant.
    Ah, but I can now see I was wrong

    Thanks to everyone who corrected this error in their diagrams and calculations.
    Good job I didn't try to work out whether the AoV with a 28mm lens was sufficient

    In the interests of not leaving erroneous information, I shall amend my post above now.

    Cheers,

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    Re: Dof/point of focus

    Quote Originally Posted by shareindex View Post
    I'll be using the lens wide at 28mm because there are 3 legs side by side leading away from the camera position with a top table spanning the entire 3 legs at the top of the legs.
    . . . that's not enough additional info . . . please . . .


    WW

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    Re: Dof/point of focus

    Quote Originally Posted by William W View Post
    . . . that's not enough additional info . . . please . . .


    WW
    Hello William and other members. Thanks for getting involved with my problem. I have uploaded a diagram to explain the photo shoot and hope it will help you to decide upon the best point of focus. As I said earlier, I have viewed several DOF calculators but still require help.

    Thanks once again for any help.

    Fred
    UK

    Edited - cant see my diagram?

    Dof/point of focus
    Last edited by shareindex; 24th November 2012 at 05:28 PM.

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    Re: Dof/point of focus

    Quote Originally Posted by Dave Humphries View Post
    Hi Nikon user,

    Do you have a first name? (we much prefer them)

    You may find this tutorial helpful; http://www.cambridgeincolour.com/tut...h-of-field.htm

    A 12m DoF is required.

    The split will be something like 47%/53% (fore/aft) at the sort of focal length you'll probably be using, so in very round figures, about 11m into the shot (5m + 12/2m) would be where to focus, just shy of half way down the table.

    You don't say what your camera body is (i.e. FF or DX), which is really helpful to use a DoF calculator.

    However dialling a few figures into that shows DoF shouldn't be too much of a problem at f/11 and an 11m focus distance as long as you stay fairly wide angle.

    Welcome to the CiC forums from ....
    Hello Dave,
    Forgive the absence of my name. I'm Fred. My camera system is Nikon D700 FX. What is meant by (5m + 12/2m) . I'm slow...
    Fred

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    Re: Dof/point of focus

    Hi Fred,

    Quote Originally Posted by shareindex View Post
    What is meant by (5m + 12/2m) . I'm slow...
    The 5m distance to front edge, then half the depth. 5 + (12/2 = 6) = 11m

    Bear in mind I haven't built in anything to cope with the elevation, which imparts slightly longer distances.

    If you Edit your profile, you can add "Fred" into the Real Name field, plus a rough location in the Location field.

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    Re: Dof/point of focus

    Hi Fred,

    With the confirmation you have given that you are using an FX D700 I have had a look again at DOFMaster which gives the following info that should assist in your question;

    " I have uploaded a diagram to explain the photo shoot and hope it will help you to decide upon the best point of focus. As I said earlier, I have viewed several DOF calculators but still require help."

    Taking it that you will be using a FL of 28mm and your camera distance is 5mtr from the closest subject (head) there are 'options' as follow;

    1) Using Hyperfocal Distance

    ..... the hyperfocal distance setting ... is simply a fancy term that means the distance setting at any aperture that produces the greatest depth of field. How to Use Your Camera, New York Institute of Photography, 2000............

    For the D700 with a FL lens of 28mm at F11 this is given as 2.34mtrs. Therefore if you focus on a point 2.34mtrs from the camera, everything between 1.17mtr to infinity will be in focus. As there's unlikely to be anything in front of you at that distance you could focus on the closest persons head.

    2) Subject to Distance Focusing

    If you focus on the head of a person half way down the table the subject distance will be approx 11.5mtrs from camera.
    For the D700 with a FL lens of 28mm at F11 DOFMaster gives the following data

    Focus Near Limit - 1.93mtrs
    Focus Far Limit - infinity

    So from the above two methods it confirms that you are safe to focus on any point between the nearest person and the person half way down the tables. BUT, to allow for errors I would suspect it's 'safest' to focus approx 1/4 of the way along the tables length. You will of course have to lock focus on this point before re-composing.
    Last edited by Stagecoach; 24th November 2012 at 07:14 PM.

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    Re: Dof/point of focus

    As a follow on from the focusing info and looking again at your table layout / shooting distance sketch I knocked up the below FOV diagram.

    It appears that at the shooting distance you give at 5 mtrs (I have calculated 5.5 if stood on a stage) the angle of view with the 28mm FL which is 65 deg will be insufficient to include the far corners of the tables nearest to you.

    It may be that you are able to move back ?

    Dof/point of focus

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    Re: Dof/point of focus

    Quote Originally Posted by Stagecoach View Post
    It may be that you are able to move back ?[/IMG]
    Or;
    a) Do a fairly quick double shot pano capture (and stitch down the centreline)?
    b) Hire/borrow a wider lens for the day?

    If doing a), bearing in mind flash recycle time - try not to get the same waiter in both halves
    (everyone else will be fairly static)

    Cheers,

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    Re: Dof/point of focus

    You had best use the focus near the centre option as per dof master. The other is more appropriate for landscape type use but there is a need with that one to consider how well in focus which in turn is dependent one how and at what size the final image is seen and how good detail needs to be reproduced. The latter one annoys me at times as it's demonstrated with small web resolution shots without pointing possible problems out. The dof field master on line calculator is giving you 2 options really. One where the camera is focused at 11.5m and the other where it is focused much closer. The difference is that the focus to 11.5m will only produce a circle of confusion of 0.020mm at a distance of 2.67m from the camera. There after it will me smaller. At the end of camera models direct circles of confusion are listed. In your case focused at 11.5mm the circle of confusion at 5m is about 0.008mm. This leaves some latitude over what are purely theoretic figures - not a bad idea. These calculators never mention is physics, diffraction problems. In simple terms that limit is 0.00068xFratio, 0.0075mm in your case at F11 but that is for a perfect lens. The real figure could easily be twice that, Maybe even more. I would say from my own experience that with decent lenses F11 along with pixels around 0.005mm is the slowest aperture that can be used for for good final circles of confusion. Go to F16 and it may be possible to see a difference. Testers may find a difference slower than F5.6 but when colour is concerned things are a little different as more pixels are involved.

    How big a print these settings can produce for close viewing all over depends to a large extent on the quality of the lens. Complicated by jpg compression etc and what is in the scene. Maybe that is best illustrated by recent talk on here about super zoom bridge cameras. A shot may have a tree in it that looks ok but examined closely the detail isn't really there. Move up to a dslr and it will be. A sillier example is to say you needed to show detail in the eye brows of a person right at the far end of the table. That would dictate a minimum print size otherwise people would be able to see them. Printing at 300 or 600dpi would also have it's effects. All in all this boils down to using the figures dof calculators provide to produce the best results you equipment can achieve. The quality in real terms will vary but it should be maximised.

    When you say you have plenty of light I assume that you will be using flash? There is another problem there. The exposure will vary along the length of the table. Not too much of a problem on old fashioned flash guns with a calculator one the side as the effects can be seen directly. I suspect you will have to take steps to ensure the nearest people aren't blown out and correct for the furthest with post processing.

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    Re: Dof/point of focus

    Quote Originally Posted by Stagecoach View Post
    As a follow on from the focusing info and looking again at your table layout / shooting distance sketch I knocked up the below FOV diagram.

    It appears that at the shooting distance you give at 5 mtrs (I have calculated 5.5 if stood on a stage) the angle of view with the 28mm FL which is 65 deg will be insufficient to include the far corners of the tables nearest to you.

    It may be that you are able to move back ?

    Dof/point of focus
    Hello Grahame,
    Thanks for your info. Yeh, 5mtrs was approx but I will be able to move back. Since posting my original thread I have gained the use of a Nikon 24-120mm 3.5/5.6 lens. If I use it, I take it that the point of focus will be about the same as members have suggested for my 28mm lens?
    Fred

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    Re: Dof/point of focus

    Hello John,
    Thank you for your interesting thread. Yeh, I will be using my 2 Bowens to bounce light off the white ceiling. One is 2/3 down the left side and the other about 1/3 down the right hand side. The Bowen stands will be extended fully to prevent light spilling of the heads of those near the stands. My on camera Nikon SB800 will be set on full power to throw light on those nearest the camera and also trip the 2 bowens. The print will be cropped to around 10"x6" and positioned in the centre of a 20"x16" white canvas. Smaller images of the occasion will be placed around the main image to create a montage. (Thats what they want).
    I will be able to hair brush the Bowens out. Cant think of any other way to spread the light around the dining room.
    The shot will be taken in RAW.
    Thanks John for a very intesting read.
    Fred

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    Re: Dof/point of focus

    It's a very woolly subject really Fred and much depends on the detail needed in the final results but as I said it is worth going through it to maximise the results. I use the term jpg compression rather loosely as effectively something on the lines of that happens to any shot at some point and this is how compacts get away with such minuscule pixels.

    Can't advise on lighting at all. You need some one who has done something like that. I have used camera club studio type set up's and know to watch out for nose shadows but that's about it really. I would be wary from that experience of using 3 light sources on the subject. 2 nose shadows. Pass really it would be out of place for me to recommend any set up really but I would wonder about the 2 bowens either side of you used directly. The modelling lights should give some idea of the results. I have only seen a friend of mine use them in the past along with a flash meter. Commercial work rather than people. He generally used 2, one for main and the other for fill in. I would also wonder about bounce of the bowens and a wireless or wire trigger as the camera flash may complicate things. BUT as I said you really need some one who has done work like this.

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