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  1. #11

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    Quote Originally Posted by smudwhisk
    Thank you for the comments. I am fully conversent with how to focus a camera, having used a number for many years. Just having difficulties working with an extension tube, since previously have only used macro filters successfully. I may well have been too close to the subject, something I have taken in mind.
    With a 50 mm lens at its infinity position on a 28 mm extension tube, magnification will be 0.56:1 and front node-to-subject distance will be 141 mm. Since your lens is retrofocus, I have no idea where its front node is; with normal lenses, it is approximately, great stress approximately, coincident with the diaphragm. If you extend the lens by setting it to a marked distance closer than infinity, magnification will be higher and lens to subject distance smaller.

    There's no magic to extension tubes or bellows. All they do is allow a lens to focus closer than it can on its own mount by adding more extension than the mount alone offers. Your "macro filters" accomplish the same thing, increasing extension/(focal length), by reducing the lens' focal length.

    If you knew what you were doing, why did you ask for help?

  2. #12
    Bob F.'s Avatar
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    Using my SQA and 36mm tube (I do not have the 28mm one) with my 50mm lens, the focal point is about 6cm from the front lens element. Depth of focus is only a couple of mm with the lens wide open so, as others far more experienced than I have already said, it is very tight and easy to miss.

    Put the camera down flat on a table focused on infinity and move a pencil towards the lens from about 30cm out - you will see it snap in to focus. You will also see why Dave's idea of getting a macro focusing rail is a good one - probably essential for a pro (I'm not, and they cost a fortune! - OK, not a "fortune", but more than I'm willing to pay for the very few times I do MF macro) - it's often easier to move the subject than the camera & tripod...

    Good luck, Bob.

  3. #13

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    Quote Originally Posted by Dan Fromm
    If you knew what you were doing, why did you ask for help?
    Because while it worked OK with the macro rings on a 35mm SLR, I couldn't seem to get it to work on the Bronnie correctly and wondered if, since it was a tube on the end of the lens rather than a ring on the front of the lens, if there was any difference particularly as on the Canon SLR I was using a zoom lens rather than fixed.

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