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Thread: Closest focusing distance - definition thereof

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    Default Closest focusing distance - definition thereof

    I am wondering if anyone can shed light on the definition of "closest focusing distance" as used by lens makers? Specifically Olympus rate the 50mm F2 Macro closest focusing distance as 0.24m. I would have expected this to mean front of lens to object distance but it appears to be sensor plane to object? Is this the normal definition?

    My current application is to digitise some of my old 35mm slide collection from OM-2n days before they get too mouldy and decrepit. I know there are film drum copiers but I have bought a cheap extension tube slide holder with an opaque lighting screen that screws into the front filter thread. It works. It is about 100mm long and the 50mm F2 cannot quite focus on the slides but adding as little as a single UV filter allows spot on focus. I have now bought 7mm and 14mm threaded extensions (from ebay HK) which also reduce the image size a touch - the 7mm seems ideal as it reduces the image size just enough to get the full 34mm width (landscape) of typical slide mounts into view.

    The cheaper 35mm F3.5 Macro obviously focuses much closer (advertised 0.146m) but produces wide black borders with this length of slide holder unless you use the EC1.4 as well. This does also work though presumably with some loss of sharpness.

    Coming back to the 50mm F2 I seem to have what I would call a close focus distance of about 105mm to the lens body and 110mm to the front glass lens. Measuring sensor to subject distance looks like the advertised 240mm as best I can tell where the sensor is.

    Mike

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    Default Re: Closest focusing distance - definition thereof

    Quote Originally Posted by mikebbh View Post
    I would have expected this to mean front of lens to object distance but it appears to be sensor plane to object? Is this the normal definition?
    Yes, IIRC it has always been this definition, in film cameras it was film plane to object.
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    Default Re: Closest focusing distance - definition thereof

    Many thanks for the quick reply.
    One up to this forum as I could not find answer anywhere else on line.
    Mike

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    Default Re: Closest focusing distance - definition thereof

    That's why there's a symbol on the camera that shows the "film" plane, so you could actually measure the distance if necessary.
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    Default Re: Closest focusing distance - definition thereof

    Quote Originally Posted by mikebbh View Post
    I have bought a cheap extension tube slide holder with an opaque lighting screen that screws into the front filter thread. It works.
    Mike, can you give a link to the product?

    The idea of using UV filters to move it out from the 50mm a bit is brilliant, BTW. One thing you might consider is taking the glass out of the filter -- look for a retaining ring with notches 180 degrees apart you can unscrew, or you could carefully break the glass out.
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    Default Re: Closest focusing distance - definition thereof

    Need to add that compacts don't use the sensor plane, they use distance from the front element in their specs, which adds considerably to the confusion. e.g., If I went by my LX3's specs, the close focus distance would have the subject inside the lens using the sensor plane.

    Cheers,

    Rick

    Quote Originally Posted by jnicklin View Post
    That's why there's a symbol on the camera that shows the "film" plane, so you could actually measure the distance if necessary.

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