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Thread: M Lens DOF marking for use on M8.2

  1. #1
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    M Lens DOF marking for use on M8.2

    I have a feeling that what I am doing is not conservative enough for digital files. I am using a 2-stop factor. For example, if I shoot at f/8, I use the markings for f/4.

    I think a 3-stop factor might be necessary given the following,
    - crop-factor means additional 'enlargement' is needed for a given print size
    - larger print sizes are more accessible than when DOF calculation parameters were determined
    - viewers tend to view prints 'too close'

    What's your thought?

  2. #2
    Subscriber robsteve's Avatar
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    Re: M Lens DOF marking for use on M8.2

    If you want something critically in focus, you have to focus on it and not rely on DOF.

    It may actually be counter intuitive now that we are shooting digital and pixel peeping. For examples, we may want to tend towards the distance side of the DOF. Distant objects will tend to be finer detail and if the DOF doesn't cover them they will look soft and no amount of USM will correct for this. Closer subjects will have larger details, but if these larger details are slightly soft they will sharpen up better with USM or other sharpening techniques.

    This is all just my guess at it and others may be able to explain it better. In my own tests, even with a 15mm, infinity objects were sharper with the lens at infinity, even when stopped down a bit. I found a fair compromise was to have the lens slightly before infinity. If I used any of the DOF marks on the lens ( a VC 15mm) the more distant parts of the scene were just not sharp.

    Robert

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    Subscriber robsteve's Avatar
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    Re: M Lens DOF marking for use on M8.2

    I found my old post on the Leica user Forum with the 15mm DOF test pictures. You can try testing your lenses to figure out which settings give you the best compromise.

    Here is the older post :


    As promised, here are my tests with the 15mm. My conclusion was at any aperture, if you want perfect infinity focus, set the lens at the infinity stop. The best compromise for near objects and infinite objects was with the lens at f6.3 and the centre of the infinity mark aligned with the first vertical bar on the DOF scale. this is the mark between the f4.5 mark and the center mark.

    These were also shot with a 39mm 486 filter fitted. I used Lightroom to convert and load the file in photoshop as a PSD and then used the PanoTools radial luminance to correct the cyan corners. I then saved the PSD and did the crops via Lightroom, using the PSD as the source, rather than the original DNG.


    First, here is the whole image. This is the one with the infinity focus aligned at the first vertical bar, just inside the f4.5 printed on the DOF scale.




    Here are the details from the top of the image. The first is with the lens focused to the infinity stop, the second with the infinty set to the first vertical mark on the DOF scale.






    In the same order, infinity focused first, from the bottom right corner.





    With the lens focused just before infinity, the DOF works better with the closer details, while still getting decent infinity focus.

  4. #4
    Senior Member ecliffordsmith's Avatar
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    Re: M Lens DOF marking for use on M8.2

    Hi Rob,

    That is a very interesting tip, thanks for sharing it.

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