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Depth of field with close up lenses

Discussion in 'Tips and Techniques' started by stepfen, Jan 26, 2019.

  1. Rollin

    Rollin Professional Photographer

    # of Dives: 500 - 999
    Location: Belgium
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    Focus distance is covered within magnification

    With a close up lens, the magnification increases so the dof decreases.

    Say, you have a magnification of 1:1 and a aperture of f:1/16. Whatever optics you use to get to this and whatever the focus distance, in the field the dof will be the same.

    Of course, there is much more to this like circle of confusion etc. But these are the basics.
     
  2. Chris Ross

    Chris Ross Barracuda

    # of Dives: 200 - 499
    Location: Sydney Australia
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    Changing lenses on any given camera won't change your depth of field as stated above the DOF is set by magnification on the sensor and aperture - as you put on higher magnification the DOF decreases. If you look at a DOF calulator is shows that at f22 and 30cm distance and 50mm focal length you should have 25mm DOF. But you are using close up lenses to get more magnification which will reduce your depth of field. You can also find online calculators to estimate magnification with diopters and your setup will give you about 0.7x magnification at min focus and +6 diopter.

    So with your bare lens you get about 0.27x magnification and 25mm DOF. Put on a 0.6x diopter maginifcation jumps to 0.7x and DOF plummets to around 3mm.

    Now change to f10 and your DOF is 8mm with bare lens and 1.4mm with the +6, both at their maximum magnification. Both magnification and focal length influence DOF as they change the magnification.

    So you can see the difference between 1.4 and 3mm is not that much so hard to see anything in your photo, but backing off a little to reduce magnification will have a bigger impact on DOF. This is exactly what is happening with the Olympus TG4/5, because the sensor is so much smaller the magnification required to fill the frame is less so the depth of field increases. Add to this the short focal lengths they use on the small sensor to keep magnification low allows the lens to be designed to focus really close. So to get more depth of field back off a little and crop the photo or use a lower power diopter.

    Another thing to consider is how you place the depth of field, if you focus on the tip of a nudi's nose with 3mm DOF, then the area in focus is 1.5mm either side of the the focus point. In this case it looks like you only have 1.5mm DOF as the 1.5mm in front of the subject is water and the DOF is "wasted" . Better to focus on the rhinopores and have 1.5mm in focus either side of them. You need to decide what is important to be in focus and focus on that, and consider the subject orientation as well - front on/side on/at an angle etc.
     
  3. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

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    Not really, although it may sometimes appear that way. The sharpness corrections do not reverse an out-of-focus problem. they just make sharper the edges of something that is still not focused.
    Yes, but it is because by getting closer you have increased the magnification.

    Added: Oops. already answered twice above.
     
  4. Chris Ross

    Chris Ross Barracuda

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    Location: Sydney Australia
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    The OP also mentioned the Sony 30mm macro, you may find this difficult to use as the close focus with 1:1 magnification is 9.5 cm from the sensor which will be about 3.0cm from the front element or maybe 2.0cm from the port glass. depending on how well it fits your port. So maybe 0.5x might be the best you can easily achieve.
     
  5. stepfen

    stepfen Barracuda

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    Location: Greece
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    I just mentioned that lens as an example. It does not fit in my housing (which BTW has a fixed port for the kit lens only).

    My initial post was during the trip (Ambon /Indonesia) and there I could see the results only through jpgs created automatically by the camera and transferred to my mobile. The sharpness problem was due to very low amount of sharpness (or actually a bit of blurring!) the camera applies to the image during the jpg conversion.
    Back home I can see RAWs and a lot of the pictures are fine.

    So the major problem is the very limited Dof. Now it is too late to correct this. I'm just looking for affordable solutions to improve my rig, my technique or both for next time.

    I'm just curious how people with eg the TG - 5 compact camera get so nice and crisp macro images with decent Dof. That camera has a "huge" aperture (f/2 or so, I don't remember numbers exactly but higher f numbers are "artificially obtained" using neutral density filters!). Yes that camera has a much smaller sensor which helps but still, is that the only cause of this?

    Thanks
     
  6. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
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    @stepfen There are several reasons a photo can look unsharp: focus (includes not within the DOF), diffraction (too small an f-stop), camera or subject movement, and post-processing (includes in-camera processing to jpgs).
    • Focus is all about your lenses and magnification and sensor and distance-to-subject. For the macro stuff you are trying to shoot, your DOF will always be small, so you have to be clever and do things like shoot the nudibranch at an angle so that the rhinophores and much of the body are the same distance from the lens. For focusing, the best practice is to get almost focused and then rock back-and-forth a bit to bring the desired part of the animal into focus. Working on an open LCD to see focus is not the best; try and use a magnifier.
    • Diffraction: In general, you want to work in the middle of your camera's f-stop range...so if your camera goes to (say) f/22, back off and don't shoot at smaller apertures than (say) f/11. Yes, you will lose some DOF this way, but you will mitigate diffraction.
    • Movement: if you are using a strobe, that will 'stop" the movement, but you want to make sure your shutter speed is high and your ISO is low so that you don't get a lot of ambient light also exposing the picture, otherwise you rish getting a sharp image (from the strobe) superimposed on a blurred image (from the ambient light).
    • Post-processing: avoid jpg. Keep everything in RAW until the very last step (like printing). Avoid too much sharpening; it looks artificial, and also "sharpens" the truly out-of-focus parts of the image. Note there are two kinds of sharpening: in Lightroom, one is called "sharpen" and the other is called "clarity." The former works to find edges and make them sharper; the latter works on the texture, not the edges. Both can help, but neither can be used to really correct focus, or diffraction or movement problems.
    Several of the posters above have given some really good information about how it all works, and the TG-4/5, etc. Read them again and again until you understand what they are saying.

    There are no magic settings, it is all trade-offs and compromises. For many macro shooters using strobes (and dialing the strobe power up or down to get the right exposure), (a) f/8 or f/11, (b) ISO 100, (c) shutter speed 1/200 or faster, (d) fill the frame maybe 1/4 or half-way (and do the rest of the magnification by cropping in post-processing), (e) get an angle on the subject to keep your small DOF placed where you really want it, (f) hold very still, (g) work in RAW, and (h) post-process (including all kinds of sharpening) gently, all work together to give you good macro images.
     
  7. Tool Belt

    Tool Belt Barracuda

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    As tursiops noted shooting at f22 can add diffraction artifacts which may add to the blur of fine details.
     
  8. stepfen

    stepfen Barracuda

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    Thanks for all the help so far. Here is a link to the best pictures I've got from nudies and slugs:
    Nudies - Google Drive
    I intentionally included some "so so" ones that I'd normally discard, for you to see.
    Overly I'm quite satisfied with the result although a deeper Dof would vastly improve a lot of shots.
    Apparently on top of everything else I also need to improve my creativity/composition skills :S
    Crabs, shrimps, fish etc to follow.
    Any feedback is welcome
    Cheers
     
  9. Chris Ross

    Chris Ross Barracuda

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    Location: Sydney Australia
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    The Nudis look fairly typical, the one factor that's hard to judge is the size of the nudi and resultant magnification. I note you are using f18 or f14 and there are some that placing the focal plane a touch further back could be a benefit - you can see in focus sand etc in front of the subject. For example the big ceratasoma nudi (....6459.jpg) I would expect more DOF as I believe it's a sizable nudi, but it is confined the rhinopores area, I would hazard a guess that much of the DOF is in the water in front of the nudi.

    Another thing to try is focus peaking, if you get that happening, you can rock back and forth and judge where to hold to get the focal point where you want it. You can see the peaking moving back and forth over the nudi as you move.
     

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