Extended-Zoom Point and Shoot Cameras

Discussion in 'Ask B&H Photo' started by Chuck-B&H, Dec 2, 2010.

  1. Chuck-B&H

    Chuck-B&H B&H Photo Specialist S.C. Charter Member

    56
    Aug 5, 2010
    New York
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  2. Mal

    Mal SC Veteran

    275
    Sep 23, 2010
    Liverpool / UK
    Chuck....

    Good read, and you could be the very man to ask a question I have been after an answer to for a while.... When a camera says for instance it has an 8x zoom.... if I pick up and look through an 8x monocular/binocular, the focal image in the latter is quite a bit larger. This being the case how do manufacturers measure the focal lengths of cameras, in relationship to times (x) rather than mm?

    In the report you have shown... this discrepancy shows itself once again...

    Nikon....................... 10x = 30-300mm

    Both Sony's............... 10x = 25-250mm

    Lumix ZS7................. 12x = 25-300mm


    If I included the rest it would become even more confusing.... How can the Nikon be 2 muliplications less than the Lumix, but only 5mm difference in actual focal length... And if we compare Sony to Lumix we could surmise that 1x = 25mm, but in order for that to work out you would have to have a starting focal length of 0 mm.

    I don't mean to put you on the spot here.... :confused:
     
  3. Chuck-B&H

    Chuck-B&H B&H Photo Specialist S.C. Charter Member

    56
    Aug 5, 2010
    New York
    Hello,

    They have nothing in common.

    With regards to Optics, a 10x binocular would make an object look 10 times larger than you naked eye.

    Photographic Lens Focal length has 2 very distinct meanings.

    The first is the technical description of the optical formula used in the lens design.

    Focal length is defined as the distance between the film or imaging sensor area (known as the focal plane) and the optical center or nodal point of a lens focused at infinity. So a 50mm lens’s optical center would be 50mm’s from the film or sensor plane at infinity.

    The second is our interpretation of what the lens will do for us while photographing.

    We describe a 50mm lens as being a normal lens. “Normal” lenses have focal lengths approximately equal to the diagonal length of the focal plane. The diagonal length of 35mm film is 42mm’s. 40-50mm lens are generally regarded as normal lens. Normal lens have an angle of coverage of approximately 46 degrees, which corresponds to our own vision.

    So a camera with a 50-100mm lens would have a 2x optical zoom lens.
     
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  4. Djarum

    Djarum SC All-Pro S.C. Charter Member Subscribing Member

    Jul 10, 2010
    Huntsville, AL
    Real Name:
    Jason
    Very different things. Sort of. If you really want to guesstimate, a 50mm lens on a 35mm is around 1x, or what our eye sees in terms of film. So, using a 10x binocular would be similar to hooking up a 500mm lens to a 35mm camera.

    Now, I hate the term "normal" because there are two seperate versions of the definition. Some say it is normal strictly due to how close a 50mm lens is to the diagonal of 35mm film, regardless of what our eye sees. Others argue normal is about what our eye sees. And of course, if you change aspect ratio, it even muddies things up further because the diagonal changes.
     
  5. Djarum

    Djarum SC All-Pro S.C. Charter Member Subscribing Member

    Jul 10, 2010
    Huntsville, AL
    Real Name:
    Jason
    I liked the comparison table at the bottom, but I think what should also be important is the size of the sensor, sensor type, and speed of the lens.
     
  6. Fuddlestack

    Fuddlestack SC Regular

    138
    Dec 1, 2010
    Alsace, France
    What happens with the monocular is that the objective lens throws an image of the target some way down the barrel, and the eyepiece acts as a magnifying glass to look at this. When you do this, you see an image that is 8 times larger than that which you would see with the naked eye. The image in the barrel is upside-down relatve to the target, but monoculars and terrestrial telescopes include extra lenses or prisms to cancel the inversion. The 8x figure of your monocular is derived by dividing the focal length of the objective by that of the eyepiece. On astronomical telescopes, which have interchangeable eyepieces, you achieve greater magnifications by using eyepieces of shorter focal length. In a camera there is no eyepiece, and the image thrown by the objective lens is formed directly on the sensor.

    The 10x zoom factor quoted for a camera is simply the ratio of its greatest and smallest focal lengths, and has no relation to the actual size of the image.

    In speaking of focal lengths such as:

    Nikon....................... 10x = 30-300mm
    Both Sony's............... 10x = 25-250mm
    Lumix ZS7................. 12x = 25-300mm

    the word equivalent is missing. What needs to be explained is that if the sensor diagonal of each of these cameras were enlarged to match that of 35mm film, then the focal lengths of their lenses would need to be scaled up to the lengths cited above.

    Hope I haven't been too confusing, it's pushing 23h00 here.
     
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  7. Fuddlestack

    Fuddlestack SC Regular

    138
    Dec 1, 2010
    Alsace, France
    I believe Barnack only fitted 50mm lenses to his first Leica because Leitz had an overstock of them at the time. A 42mm lens is much closer to true "normal".