Depth of Field ~ distances and zoom lenses

Discussion in 'Photography Beginners' Forum' started by PJcam, Jan 26, 2018.

  1. PJcam

    PJcam No longer a newbie, moving up!

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    I totally agree, as will all on here I think, Bryan Peterson's 'Understanding Exposure' book or ebook is probably the best book anyone learning Photography could have, should have.

    Interestingly the book mentioned, which I am referring to in the post here is by, Bryan Peterson, I am wondering if maybe an older book based on the rep;lies so far. That said, I don't feel I should judge the book based on this one item, time will tell as I work my way through the book.

    I have today downloaded another App, called DOF easy, it has a rating of 5.0, very high. having downloaded it and checked it, along with explanations of every link, I can see why it is highly rated. There are areas in it I need to learn more about but it seems a very good App.

    Meanwhile my reading as been distracted as I am currently looking to improve my understanding of the Hyperfocal Distance Hyperfocal Distance Explained

    Thank you.


     
  2. TCampbell

    TCampbell Been spending a lot of time on here!

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    Here's a link to an online DoF calculator:

    Online Depth of Field Calculator

    You supply a few ingredients such as:
    • The sensor size (this site asks for your camera model, but it really just needs to know the sensor size. If your specific camera model isn't on the list then just select any Canon "Rebel" because they all have APS-C size sensors.)
    • The lens focal length (if it's a zoom lens then enter the focal length you plan to use for the shot)
    • The focal ratio (f-stop) you plan to use for the shot
    • The lens focus distance to your subject
    That's the info needed to compute the depth of field. BTW, there are several smart-phone apps that do this for you. So if you want an app when you're out shooting instead of at your computer... you can get an app to work this out.

    Suppose we enter a few values by picking a Canon Rebel body, pick a 50mm lens focal length, pick f/8 as our focal ratio, and decide to focus the lens to 10 feet.

    When you click the "calculate" button, the values on the right side of the table are updated and it tells us that everything from 8.46 feet to 12.2 feet will be in acceptable focus ... for a total depth of field of 3.77 feet.

    But also notice that near the bottom of those values there's a number that says "Hyperlocal Distance: 54.1 ft".

    Hyper-focal distance is something you would use if you wanted to get the maximum depth of field possible with that specific camera body + lens focal length + f-stop combination.

    To show how that works, here's a couple of photos of my old Canon AE-1 35mm camera ... but I call your attention to the focus ring position, depth of field marks, and aperture ring on the lens.

    In this first shot, suppose I want to shoot a landscape photo with my 50mm lens... so I focus to "infinity" and I select f/22 -- thinking this will maximize my depth of field (it turns out it will not... more on that in a moment). Here's the photo of the camera & lens showing how I've set the focus and f-stop:

    Infinity.jpg

    If you look at the the line that marks the focus (in the center of the yellow oval between the "22" and the infinity mark on the focus ring) you'll see a set of numbers that mirror each other... "22 16 11 8 4 | 4 8 11 16 22". Those are "depth of field" marks and were extremely common on old manual focus lenses. It means that if you select f/22 (as I have in this photo) then everything from the "22" on the left to the "22" on the right will be in acceptable focus.

    But here's the thing... the "22" on the left is probably somewhere around the 12 ft distance (it's between the 10 and 15) and while that goes to "infinity" at the focus point, there's nothing beyond infinity. So there's a range of distance that could have been in focus ... but I'm not taking advantage of it if I set up my focus like you see in the image above. I am wasting some of my depth of field.

    So here's another image and you can see I've changed my focus position in this next photo.

    Hyper-Focal.jpg

    I've annotated this image with a green oval, a yellow oval, and a blue rectangle.

    First, I've selected f/22 -- as indicated by the green oval.

    Second, and this is the important part... instead of focusing to "infinity", instead I adjust the focus ring so that the "infinity" mark is lined up with the "22" on the far side of the depth-of-field scale. I've circled in yellow in the photo above.

    Third... as a result of doing this, everything between the "22" left of the focus position and the other "22" to the right of the focus position (on my depth of field scale) should be in acceptable focus. I've placed a blue rectangle over that range. You can see it's roughly everything from 6' to infinity that will be in focus. Recall in that in the first image... only subjects from 12' to infinity were going to be in focus. So I've increased my depth of field by doing this.

    This "hyper-focal" distance only applies to this combination of lens focal-length and f-stop and for this film size. If we changed the film or sensor size ... or if we changed the lens focal length ... or if we changed the f-stop, then the hyper-focal distance would calculate to a different value.



    Landscapes are often shot with wide-ish angles of view (short focal length lenses.) Short focal length lenses naturally increase the depth of field. If you were to punch in values for your 18-55mm lens and use the 18mm focal length, say... f/16... then the DoF calculator says that Hyper-Focal distance is 3.56 ft (meaning if you were to focus on something 3.56 ft away then you'd maximize the depth of field) At that combination, everything from 1.88 ft to infinity would be in acceptable focus. You can see how using wide-angle lenses makes it pretty easy to get a broad depth of field.
     
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  3. PJcam

    PJcam No longer a newbie, moving up!

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    @TCampbell

    Many thanks for your detailed reply, the notes supplied and the images are very clear and most helpful.

    Most modern lenses don't have the details you show in your example.

    You mentioned obtaining Apps for a mobile phone, I downloaded two yesterday
    DOF Calculator - Aimen RG and
    DOF - Jonathan Sachs

    Both look OK although one is better than the other.

    DOF Easy is another App I found earlier today, it has a rating of 5.0 which is very high, most are 4 to 4.5 ratings. Having opened the App to look at it I can see why it is rated so well, not only is it easy to follow, every links has a detailed explanation to guide you through what they mean.

    Back to :icon_study:
    :encouragement:
     
  4. Garasaki

    Garasaki TPF Supporters Supporting Member

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    So I understand that as your experience with photography grows, things such as calculating DoF can be learned and practiced, and one of the primary advantages to doing so would be getting the shot you want, and at the same time not MISSING the shot when it's there.

    I am not trying to minimize the importance of knowing your DoF. Particularly for some shots professionals might be going after.

    However, another way to learn about DoF is take freakin pictures. It's a digital camera. You can take thousands of photo's at no cost. I've learned a lot about DoF by taking pictures, and yes I definitely lost some shots due to using too narrow a DoF. As I'm learning more, I'm losing less shots because of this. I'm considering a "generalized" DoF when setting up my camera and my shots.

    It's not nearly as precise as mathematically calculating it. However, I also don't carry a tape measure when I shoot...

    I feel like this is a subject that can be overcomplicated and overwhelming for a less experienced photographer on their journey (while fully acknowledging that it IS an important subject).

    I would suggest perhaps all the book learnin here is swinging too far in one direction....
     
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  5. ac12

    ac12 No longer a newbie, moving up!

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    Tim's pix shows the DoF scale on the lens.
    This was sooo easy to use, and I used it often.
    It is one of the things I really miss on today's lenses.
     
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  6. john.margetts

    john.margetts No longer a newbie, moving up!

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    I miss it as well, but my latest lens - Canon EF 70-300 - has an LED dislay which can show DOF.
     
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  7. PJcam

    PJcam No longer a newbie, moving up!

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    I totally agree with the need to get out and test the camera but, the weather here has been terrible so I have been unable to do so yet.

    I have three different DoF Calculators, including www.cambridgeincolour.com and every one showed different results? I have an idea on the concept, just need to get out and play with it and check the results.

    I also have an App for Hyperfocal distance called, HyperFocal Pro, this is a very good App for checking settings for a deeper DoF, but again, I need to get out and put these things into practice.

    Thanks for your comments.
     
    Last edited: Feb 2, 2018
  8. PJcam

    PJcam No longer a newbie, moving up!

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    It looked a good items to have on the lens, I wonder have they done away with this because lenses are more advanced, more automated (if you want automated), and maybe also to cut costs.
     
  9. PJcam

    PJcam No longer a newbie, moving up!

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    Where is the LED display John?

    I have the EF-S 75-300mm f/3.5-5.6 Lens

    Pity they did away with the old method I think.
     
  10. john.margetts

    john.margetts No longer a newbie, moving up!

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    The LED display is on top of the lens barrel just forward of the mount. You can select between focus distance, DOF, and something else that escapes me at the moment (edit: image stabiliser status). See here for a photo: Buy Canon EF 70-300mm f/4-5.6 IS II USM Lens
     
    Last edited: Feb 2, 2018
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  11. petrochemist

    petrochemist TPF junkie!

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    DOF displays were easy with push pull zooms, but become much more awkward with two ring zooms as most are with AF taking over. It's a shame more bodies don't offer a hyperfocal focusing option. It can't be difficult for the lens to focus to a fixed distance depending on the aperture. Ideally such a system would allow user adjustment of how sharp they consider acceptable (electively circle of confusion adjustment).

    IMO primes have no excuse not to show a DOF scale on the lens, but some don't even give focusing distance scales...
     
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  12. Dave442

    Dave442 No longer a newbie, moving up!

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    I think the digital display option like that Canon lens is a nice feature. With this data on the lens it would be nice if it could be added to the EXIF. This digital reading resolves the issue with two rings zooms and how to show the changing DOF at the different focal lengths (the old Nikon 43-86mm zoom may not have been great, but the curved lines showing DOF were a thing of beauty).
     
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