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Thread: Beginner trying to understand DOF calculator use

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    Beginner trying to understand DOF calculator use

    I have just recently begun to develop a real interest in becoming a proficient photographer; strictly for my own pleasure, no professional intent. Having taken snapshots most of my life I have been aware of depth of field and how it is influenced by aperture. As I've been doing some reading to better understand the use of depth of field in producing better photographs I have come across DOF calculators. When planning a shot do people often use a depth of field calculator? If so, I'm struggling with how one knows how far from the camera the focus is. I'm using a Sony NEX-6 (only recently acquired) and short of taking a tape measure in the field and manually focusing and then measuring I don't see how one might calculate a depth of field.

    Perhaps I'm over thinking this, not unusual for me, but I can see how having an accurate value for depth of field could give one tighter control over the elements of the photograph.

    Any insight and/or suggestions for further readings is appreciated.
    Thanks from a new guy,
    Andrew

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    Re: Beginner trying to understand DOF calculator use

    Quote Originally Posted by AndrewMcD View Post
    Perhaps I'm over thinking this, not unusual for me, but I can see how having an accurate value for depth of field could give one tighter control over the elements of the photograph.
    More than likely, yes, you could very well be overthinking this. I mainly photograph people and I very rarely ever use a DoF Calculator.

    What generally are you thinking of Photographing?

    WW
    Last edited by William W; 11th May 2013 at 08:19 AM.

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    Re: Beginner trying to understand DOF calculator use

    To Bill's comment I would add that I cannot see the relevance of DoF tables and calculation to working with modern equipment which often doesn't have any distance scale on the lens ... one would have to perform a highly circuitous process with perhaps tape measure and using a highly selective AF to focus on something at the required 'focus point'. They are of course useful as a guide to what is likely. All DoF is a qualitive assessment by the viewer and differs with the situation and use of the photo.

    The last time I felt I needed to worry about it I focus stacked with two exposures to make sure both essential focus points were sharp. It wasn't two people but it could well have been and would have worked just as well with people as cooperative as my non-humans were.

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    Re: Beginner trying to understand DOF calculator use

    The beauty of a digital camera is that you can blow up the image in the camera's LCD to closely examine the depth of field. You can also take multiple photos of a scene using different aperture settings at no extra expense (unlike when using film) and decide later when viewing the images on a computer monitor which depth of field is more satisfying. All of that renders a depth of field calculator needless to me when taking a particular shot.

    Depth of field calculators are useful to me for providing a general understanding of what the depth of field will be. As an example, when using a 200mm lens at about 8 feet at f/4, the depth of field is only about 1/2 inch. Having the general understanding of how small the depth of field is in that circumstance is helpful to me because the information makes me realize that depth of field in similar situations is much smaller than I would intuitively think would be the case.

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    Re: Beginner trying to understand DOF calculator use

    Hi Andrew,

    Here are my thoughts, although I'm not sure they'll be much help to you

    Back in film days, when most of us shot with prime lenses which needed to be manually focused ....
    We could look at the scene, assess the closest and farthest points of our composition needed to be sharp, then use the DoF scale marked alongside the focus scale, and set aperture and focus distance (without even looking through the V/F ) to ensure these were covered - ah, the good old days

    Zoom lenses rendered most lens DoF scales impractical, aside from some curved coloured lines on some zoom barrels.

    The AF became the norm which meant smaller focus rotational amounts leading to compressed scales (and the loss of the infinity end stop) - some cheaper lenses don't even have a distance scale these days, even primes.

    We also lost the aperture ring on some brands, as aperture is often set in camera these days.

    All of these factors do make it far more difficult to actually use a DoF calculator effectively 'in the field' - so these days I go by experience/gut feeling (when DoF is important to me) and this can be supplemented by review and zoom on LCD and memorising DoF tables as Mike and jc have said.

    Then again, other factors like maintaining a suitable shutter speed and iso combination may take precedence depending upon the subject and of course, if you're only shooting for the web; getting the subject big in the frame, downsizing and effective sharpening technique can improve matters significantly.

    I have a DoF calculator app. on my iPod Touch, but I have never actually used it in the field.

    Welcome to the CiC forums from ...
    Last edited by Dave Humphries; 11th May 2013 at 11:17 AM.

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    Re: Beginner trying to understand DOF calculator use

    I occasionally use DOF calculators when I am analysing someone else's photographs when trying to offer some assistance. For my own photography I just use the DOF preview button if it is critical. With experince I think you develop a bit of a feel as to the DOF for different focal lengths and focusing distances and select an aperture that is safe. If you know it is marginal you check.

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    Re: Beginner trying to understand DOF calculator use

    Hi Andrew,

    I'm the odd one out. I do fine a DOF chart (or its electronic counterpart) somewhat useful.

    I agree with most of the comments above. Modern equipment has made DOF charts much harder to use, because of zoom lenses and short-throw focusing. And digital has made the charts less important because you can (1) check DOF after a shot, by zooming the lcd, and (2) shot again at zero cost. In addition, for a lot of the photography I do, a chart simply isn't very helpful. For example, in shooting candids of people, I have a pretty good feel for the DOF I will get a different apertures, so I just select what I think will be a good choice to start and check after a shot or two.

    However, I still sometimes find a DOF chart helpful in doing landscapes. Perhaps that is because I don't do landscapes all that often, but even after years of photography, I still don't have a good enough feeling for DOF in landscape applications. In particular, I sometimes find it helpful to consult a chart before framing a wide-angle shot that has both foreground and background detail. I also find a chart helpful in night photography, where I really don't want to spend 20 minutes generating a test shot and where DOF preview is impossible to use. True, you can't precisely apply the information because of the lack of a decent scale on most modern lenses, but it is helpful as a rough guide.

    I don't carry a chart. I just keep a couple of apps on my phone. the one I like best is called "field tools depth of field guide."

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    Re: Beginner trying to understand DOF calculator use

    Wow! I am impressed with all the great responses. As I was beginning to suspect it appears that doing DOF calculations is more an interesting academic exercise that helps with insight rather than a tool used on a regular basis. As I'm still trying to wrap my head around the technical aspects I think some of my confusion is brought on by autofocus. Acclimating myself to using the different types of AF (Multi, Center, or Flexible Spot on my Sony NEX-6) in consideration with desired depth of field for the particular picture isn't, at this point for me, the least bit intuitive but with your help I'm making progress.
    Thanks for the help,
    Andrew

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    Re: Beginner trying to understand DOF calculator use

    Quote Originally Posted by AndrewMcD View Post
    Acclimating myself to using the different types of AF (Multi, Center, or Flexible Spot on my Sony NEX-6) in consideration with desired depth of field for the particular picture isn't, at this point for me, the least bit intuitive but with your help I'm making progress.
    If your camera has Live View and manual focus capabilities, using them might help the concept become more intuitive, especially if you are shooting at a distance of three feet or less on a tripod. Using the tripod allows you to set up the situation and then be concerned only about looking at the changes that occur when you make adjustments to the aperture, the focus or both. The relatively short distance will automatically throw much of the subject out of focus (perhaps surprisingly so) even when using smaller apertures. Using manual focus and then blowing the image up really large in Live View makes it easy to see the limits of the near and far sides of the depth of field.

    Once you have a feeling for depth of field in those situations, you'll hopefully more intuitively appreciate the impact of depth of field and focus point on more distant subjects, especially if you go through the same exercise described above though using more distant subjects.

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    Re: Beginner trying to understand DOF calculator use

    Andrew,

    The type of AF is mostly irrelevant. The AF method you choose tells the camera what elements in the scene to use for focusing, and therefore where the focal point will be in the image. It is aperture and distance that determine DOF. The only connection I can see between the two is that depending on the AF method you choose, the camera may place the focal point closer or farther away from you, and if the focal point moves foward or back, so do the near and far limits of depth of field.

    Dan

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    Re: Beginner trying to understand DOF calculator use

    IMO, DOF charts were never quite useful. Not that knowing the DOF was not useful when shooting with rangefinder cameras. DOF charts were never part of my shooting procedure. However, rangefinder camera lenses had DOF scales built in. Some earlier SLR lenses also had the DOF scale...

    Beginner trying to understand DOF calculator use

    As an example, the focus point of the above lens is the yellow line. You have a double set of f/stop indicators situated to the left and to the right of the yellow focus line. When, you were using a specific f/stop and were focused at a certain point, you were in acceptable focus (definition of DOF) between where that f/stop indicator to the left of the focus line and where that f/stop indicator to the right of the focus line matched up with the distance indicator.

    BTW: the red dot was the point at which infra red focused.

    You need to remember that there is only one point of perfect focus, DOF is the distance between the nearest and furthest point of "acceptable" focus.

    As was mentioned above, most AF lenses have a very short throw from the closest point of focus to infinity. Combined with that short turning radius, many of the AF lenses have done away with focus scales entirely. This also reduces the value of DOF charts.

    OTOH, I think that studying DOF charts for your lenses can give you a good idea of the DOF you will have when shooting. I can have a good idea of the DOF I will be shooting with because I have perused the DOF charts prior to shooting. But, I don't really use a DOF scale while shooting.

    Many photographers want the widest aperture possible when shooting portraits. I disagree with this and seldom use anything wider than f/4 (mostly quite a bit smaller) for more DOF. I don'tlike one eye being in focus and one eye being OOF.

    Many (most) cameras have a DOF preview button which will stop the lens down to view your image at the shooting aperture (you normally view at the maximum aperture). This is not really all that great. It is usually quite dim to view when the f/stop is at the shooting aperture.

    You "CAN" use live view and enlarge the image view. However, this is quite a slow process and just about impossible for moving subjects.

    My advice is to shoot, shoot and shoot some more until you can get a good idea of what your lens/camera combination will capture at different f/stops, different focal lengths and different points of focus. That is the advantage of digital photography. It costs nothng to experiment and experimentation will help you get comfortable with your equipment.

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    Re: Beginner trying to understand DOF calculator use

    Quote Originally Posted by DanK View Post
    The type of AF is mostly irrelevant. The AF method you choose tells the camera what elements in the scene to use for focusing, and therefore where the focal point will be in the image. It is aperture and distance that determine DOF.
    HI Andrew, Dan,

    I'm not entirely convinced by this statement, although I have no proof to back my claim.

    Sure, it is true if you use one focus point only - which is how I shoot with my DSLR, I choose what to focus on and I set the aperture to achieve what I think is sufficient DoF, or I might even crudely, manually 'bracket' as well.

    However, if you use some kind of "intelligent AF" option, I have seen these (admittedly on a P&S camera), identify the areas they consider to be 'important' in a scene and for these to be at different distances from camera - what's to stop the AF determining best focus for both distances and choosing (at very least) to set the focus distance to be say, mid-way between them?

    That kind of does the hyper-focal calculation for you

    If the whole camera is on "Intelligent Auto", that distance information could also be used to choose an appropriate aperture, letting the exposure be corrected by automating iso and shutter speed choices.

    Well, that's how I'd design it anyway! So if they don't work like that, they're missing a trick.

    Quote Originally Posted by DanK View Post
    The only connection I can see between the two is that depending on the AF method you choose, the camera may place the focal point closer or farther away from you, and if the focal point moves forward or back, so do the near and far limits of depth of field.
    Perhaps we are on the same wavelength Dan

    Now I have no idea what modes Andrew's NEX-6 is capable of, far less which he was using, but I think AF mode might be relevant.

    EDIT:
    Richard's image demonstrates how my film-days focus "Max DoF" method worked, if f/22 is selected at the focus distance shown (12' or 3.5m), everything from 6' or 1.8m to infinity should be sharp enough.

    Cheers,

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    Re: Beginner trying to understand DOF calculator use

    DanK,
    " The only connection I can see between the two is that depending on the AF method you choose, the camera may place the focal point closer or farther away from you, and if the focal point moves foward or back, so do the near and far limits of depth of field."
    YES, your point is exactly what I was getting at! I was finding the whole AF business confusing until I came to recognize that with the different AF modes I could control the object that the camera was focusing on. (Obviously within the limits of how the AF system is implemented.)

    I can see that some of my confusion with DOF and AF is being somewhat overwhelmed by the way the camera operates. In addition I've been reading material that may pertain to older cameras (thank you Richard for the picture and explanation!) but is no longer relevant to the highly automated cameras that are now so common.

    As Mike has suggested I'll set the camera up on a tripod and systematically make changes in focus and aperture and study the results.

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    Re: Beginner trying to understand DOF calculator use

    Quote Originally Posted by DanK View Post
    . . . I'm the odd one out. I do fine a DOF chart (or its electronic counterpart) somewhat useful. . . I still sometimes find a DOF chart helpful in doing landscapes. ...
    No, you are not the odd one out. I sometimes use a DoF Application for Landscapes more than for any other type of Photography - the next is macro and close up work.That isn't saying that I use a DoF Calculator for every Landscape macro or close up shot - just saying, if I use a DoF reference, then it is usually for that type of shot.

    As I mentioned I mainly photograph people, that’s why I asked the OP what he was going to Photograph. It’s too late after the shot for me to use image review or other method to check the DoF. I need to know reasonably accurately the DoF beforehand. For my shooting I use Centre Point AF mostly 100% of the time, therefore the type of AF Mode is not a factor for me. For making photographs with people as the main subject: I know the DoF for the typical framings and for three main apertures. Those details are simple to remember, even for two camera formats. Hence my answer to the OP that yes, he is probably over thinking it. Even if LAndscape photograpy is the OP's main desire - then I think that he is probably overthinking it for a majority of his shots, becasue typically a smaller aperture will be used and the point focussed upon is most often than not, far away: arguably an accurate idea of DoF is more relevent for portraiture and sports work.

    WW
    Last edited by William W; 11th May 2013 at 08:55 PM. Reason: corrected typos

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    Re: Beginner trying to understand DOF calculator use

    Hi Andrew. I'm also a new to photography (two years). Around four months ago, I committed to learning how to set my camera for infinite depth of field. I like to use this setting for landscapes and even other situations. Remember, if you have a sharp picture you can always muddy up parts of it using software. The reverse is not true.

    Let me give you an example of what I do to set my camera for infinite dept of field. Loaded on my I-phone is a free DOF calculator by Indie Film Gear. You first have to tell the app the camera you are using and whether you want to use feet or meters in your measurement. This app assumes a circle of confusion of .00079 in (I'll let you figure out what this means). You can select a different circle of confusion if you want -- I have not messed with this.

    Once you tell the app your camera's type and model and have selected feet or meters it then takes you to a screen where you enter focal length, aperture, and distance. Putting in 1000 feet distance sets the app to a far distance of infinity.

    Here is an example I often use. Set focal length to 35 mm, aperture 11, and distance to 1000 ft. The app tells me I need to focus on an object 18'2"" away. That is my hyperfocal distance. Yes, I bring a tape measure into the field to do this exactly. Given all the other "junk" most photographers carry bringing a tape measure along is not a burden. I am now evaluating various laser measuring tapes.

    Once I have set my camera to the above specifications everything I take a picture of will be in sharp focus (.00079 in, circle of confusion) from 17' 11" to infinity.

    I hope this helps a bit.

    Karm

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    Re: Beginner trying to understand DOF calculator use

    That seems like a fool-proof system, Karm, of course assuming that there is an object 18' 2" directly in front of you.

    By the way, the quality of your photos belies that you have been shooting only 2 years. Surely that was a typo that left off a zero.

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    Re: Beginner trying to understand DOF calculator use

    Focussing at the Hyperfocal Distance will ensure the maximum Depth of Field for any given combination of:
    Focal Length of Lens
    Aperture
    Camera Format.

    BUT -
    Focussing at the Hyperfocal Distance will also: Render the Plane of Sharp Focus AT the Hyperfocal Distance.

    WW

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    Re: Beginner trying to understand DOF calculator use

    Quote Originally Posted by Mike Buckley View Post
    That seems like a fool-proof system, Karm, of course assuming that there is an object 18' 2" directly in front of you.

    By the way, the quality of your photos belies that you have been shooting only 2 years. Surely that was a typo that left off a zero.

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    Re: Beginner trying to understand DOF calculator use

    Hi Andrew,

    I'm sure that by now you have sufficient replies to understand that there are times when accurate DOF knowledge is important and times when just a basic knowledge of its affect on an image are adequate.

    As an example of a scenario where accurate knowledge of the DOF was required in pre-planning a shot there was an interesting thread here about a year ago which I will summarise.

    The member was required to take a group shot at a function where he knew the table layouts which were two long tables with space between them and running away from him with a table joining these two at the far end. He knew the table sizes, distances and where he could position himself on a stage. With this knowledge the focal length required to get all in shot was calculated and from that the point of where he must focus to ensure he had adequate DOF to include the nearest subjects worked out.

    Beginner trying to understand DOF calculator use
    The circles represent the heads of the nearest, mid and farthest persons at the table. The f11 and f8 markings show the 'near focus distance' at these two apertures if focused half way along the length of the tables.

    Whilst this is an extreme example it was necessary to give the shooter confidence that he was capable of getting all in focus. He was also aware that lighting was a limitation and although there was of course an option of stopping down to increase DOF this would have been at the cost of ISO and/or speed.

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    Re: Beginner trying to understand DOF calculator use

    Mike, the object 18'2" doesn't have to be in front of you. Once you focus at this distance you lock it in and can shoot at anything. Often I also do a 24 mm (35 mm equivalent) at f9. This gives you from 10'4" to infinity. For general shooting, I find this fun to work with.

    Actually Mike, I left two zeroes off my 2. I apologize for this small error.

    Karm

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