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Thread: Canon 5d MkIII upgrade

  1. #1
    mastamak's Avatar
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    Canon 5d MkIII upgrade

    I have just upgraded my faithful Canon 40D with the purchase of a 5D MkIII. This is a lovely camera to use and quite a challenge to master so I have been taking as many photos as possible just to get a feel for the camera. One thing I have noticed however it that it seems that the depth of field is quite pronounced when I compare with a similar photos taken with the 40D and the same lens. For example I took some pretty standard landscape shots last weekend at f7.1 and, on close examination I can clearly see the region of about 3m depth in the centre of the image in perfect focus. Outside this area the sharpness of the focus falls away. I am sure this was not so pronounced with the 40D where I could get away with f7.1 for general landscapes and only had to screw the aperture down when I really needed a particularly large depth of field. I was wondering if this is a function of the full frame sensor or perhaps I am just unused to the precision of the image of this new camera. I am guessing somewhat but I am starting to think I might have to go to f10 or higher to get the same effect as f7.1 with the 40D.
    Grant

  2. #2
    dubaiphil's Avatar
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    Re: Canon 5d MkIII upgrade

    That'll be the full frame sensor - try online depth of field calculators and see the difference between full frame and crop

  3. #3
    dubaiphil's Avatar
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    Re: Canon 5d MkIII upgrade

    And learn about hyperfocal distance as well...

  4. #4
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    Re: Canon 5d MkIII upgrade

    In fact your lens behavior should be the same on a cropped or FF body.
    What lens are you using?
    Also you have the ability to fine-tune the lens to your body using micro-adjust. For sure worth to check this out. On the internet there are several explanations how to do it in a correct way.

  5. #5
    dubaiphil's Avatar
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  6. #6
    herbert's Avatar
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    Re: Canon 5d MkIII upgrade

    Hi Grant,

    The change in sensor size does effect the apparent depth of field, i.e. how the depth of field appears when looking at the whole frame. If you were to crop into the frame to get the same size as your old crop camera then the depth of field would be the same.

    Comparing cameras requires that the focal length and aperture be converted so they can be fairly compared, i.e. made equivalent. Here is a long article on camera equivalence:

    http://www.josephjamesphotography.com/equivalence/

    I would only read it all if you are very interested. The section 'On the Super Quick' is the part to understand.

    The short summary is that if you frame up the same scene with a full frame camera and the crop camera (equivalent focal length and the same aperture) then the depth of field on the full frame camera will be reduced by the crop factor. To get the same depth of field you will have to close down the aperture by the crop factor. So your old f7.1 will be around f11 (crop factor 1.6x).

    If you care about diffraction then note that the diffraction limited aperture on the 5D III is f10.1. On the 40D it is f9.1. This is related to the absolute pixel size. The 5D has bigger pixels so has a higher limit. However you can often push far beyond the theoretical diffraction limit before your images will suffer from loss of detail. It is better to get your depth of field right for a landscape than to have a sharp central part of the image and an out-of-focus foreground/background.

    Alex

  7. #7
    mastamak's Avatar
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    Re: Canon 5d MkIII upgrade

    Thanks Phil, Hans & Alex. Very helpful comments and I am now pleased that I was not imagining anything. I am pretty sure I read the CIC sensor size tutorial some time ago but I did not understand the relevance until now. Thank you Phil for reminding me of it.
    Grant

  8. #8
    DanK's Avatar
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    Re: Canon 5d MkIII upgrade

    for an excellent summary of the effects of sensor size on DOF, check out this old posting by Bob Atkins. If you play around with DOF master, I believe you will find that the difference is approximately one stop.

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