why can't you focus when zooming all the way in?

Discussion in 'Photography Beginners' Forum' started by ph0toe, Oct 31, 2019.

  1. wfooshee

    wfooshee No longer a newbie, moving up!

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    My 70-300G ED VR does make me move back a couple of inches for minimum focus distance at 300 compared to 70. That said, I believe the distance from the front element to the subject is the same. Sensor to subject distance is different, I have to back up just a bit, and while I didn't measure, the difference is very close to the length change of the lens barrel.

    So in this case, I would say the minimum focus distance is different, measured from the sensor plane. Lens-to-subject, probably the same distance.


     
  2. Dacaur

    Dacaur TPF Noob!

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    Generaly MFD is measured from the sensor, and at whatever zoom allows the minimum focus distance.
    Whether the MFD changes with zoom depends on the lense design. Many do change, but many do not.
     
  3. ph0toe

    ph0toe TPF Noob!

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    what you mean minimum focal? isn't 24mm the minimum? and i experimented with a few different angles, like moving a few feet away as oppose to close
     
  4. Dacaur

    Dacaur TPF Noob!

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    MFD = Minimum focus distance. Measured from the sensor, it's the minimum distance at which the lense can focus. It's different for every lense. My 35mm f2.8 macro has a 5.1" MFD, which is about an inch or so from the front of the lens. 50mm 1.8 is aroun 13". My 18-135 nano usm is 15.4".
     
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  5. Original katomi

    Original katomi TPF Supporters Supporting Member

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    Refer back to post 7
    Canon home uk lists the minimum focusing distance for you lens and many others
     
  6. pocketshaver

    pocketshaver TPF Noob!

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    for what its worth, whats the lens diameter on this thing? Ive found that my LARGE diameter lenses, say the one that uses a 62mm thread on the filter has a different distance requirement from the 58mm and 52mm diameter ones.

    Took me a tad time to realize that one needs me to be about 3 feet away to USE MACRO function on it, while the other needs me about 12 inches away, the 52mm 100-300 macro zoom, but when I turn it down to 100 and toss on a x1 macro diopter I need to be 3 inches away form an object.
     
  7. petrochemist

    petrochemist TPF junkie!

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    Lens diameter is not directly related to minimum focusing distance, but longer focal length lenses will often have longer MFDs and they also need wider objectives for reasonable speeds.
    A +1 diopter in line with any lens will make it focus at 1m when set to infinity & closer at other focus settings, a +2 diopter will half these distances. Despite some manufacturers labeling there is no such thing as a x1 diopter - diopters are an alternative way of sating focal length and are simple postive (for converging lenses) or negative (for diverging lenses) numbers. For the record a lenses diopter is defined as 1/(focal length in meters).
     

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