Question about Canon Standard Zoom vs Macro lens

Discussion in 'Photography Beginners' Forum' started by nico, Dec 11, 2007.

  1. nico

    nico TPF Noob!

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    I'm looking to purchase a Macro lens, specifically the
    Canon EF 100mm f/2.8 Macro USM.

    Currently I'm using the Canon EF-S 18-55mm f/3.5-5.6 USM.
    One thing that confuses me is the closest focusing distance number for both lenses.

    The Standard lens is listed at .28m/.92 ft to infinity
    The Macro lens is listed at .31m/1 ft (film plane to subject).

    2 questions.
    1. Wouldn't the macro lens' number be lower than that of a standard lens?
    2. Could someone explain to me in laymen terms what the "film plane to subject means"?

    Many thanks :)
     
  2. YellowBay

    YellowBay TPF Noob!

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    Film plane to subject distance is simply the distance from the sensor in your camera to the subject. On top of the camera, you should see a circle with a line through it. That's the film plane (or sensor plane I suppose if you're digital).

    I think the main reason for the difference in distances is that the lens is a 100mm job, I'm sure if I can remember my formulas properly that minimum focus distance is a function of focal length squared over aperture.
     
  3. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    Every camera has a 'film plane'...basically, that is where the film (or digital sensor) sits in the camera. The subject to film plan distance is just that...the distance from the subject to where the film or sensor is.

    I'm not sure where they measure the close focus point to on the 18-55mm lens...but I would guess that it might be the front of the lens.

    Also, the 100mm lens is almost twice as long as the tele end of the other lens (100mm vs 55mm)...so that gives you more magnification. So while the minimum distance to the subject may be similar, the 100mm will give you a more magnified image.

    This is why macro lenses are often labeled with their reproduction ratio. I believe that Canon's 'Macro' lenses are all capable of 1:1 reproduction. That means that the size of the subject is equal to the size of the image on the film or sensor. It practical terms, that would mean that you could fill the frame with a quarter.

    Also, it should be noted that the 18-55mm lens does focus unusually close for a non-macro lens. Many other brands of lenses use the word 'Macro' in their name, without actually being able to get 1:1 magnification.
     

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