Olympus What does adding focal length mean?

Discussion in 'Olympus' started by Freedom, Oct 28, 2003.

  1. Freedom

    Freedom Guest

    I can get an Olympus C-210 Teleconverter. It multiplies focal length by
    1.9x.

    What does that mean in laymen terms? (like if I was shooting a 4 foot tall
    object from 20 feet away?)

    How much more "zoom in" will I get?

    Regards,

    Jeff
     
    Freedom, Oct 28, 2003
    #1
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  2. Freedom

    Rob Wild Guest

    As I understand it, the focal length multiplier is exactly that - ie:
    For the 1.9, multiply your focal length on the lens by that amount.

    eg: if you are using a 24-80mm lens, adding the teleconverter would give
    you an effective focal length of 45-152 mm, and you will generally lose
    about 2 stops. A 100mm lens will become a 190mm lens, also losing about
    2 stops.

    cheers

    Rob
     
    Rob Wild, Oct 28, 2003
    #2
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  3. Freedom

    Freedom Guest

    Losing a stop means what? Also, can it be put into a real life example with
    a distance and size of object?

    Regards,

    Jeff
     
    Freedom, Oct 28, 2003
    #3
  4. You don't get more "zoom." a teleconverter like the C-210 must be used
    at or very near the maximum focal length of the camera's zoom lens or
    you will get vignetting. In the example of the 24 - 80 lens given above
    the effective focal length will be 152mm. You might be able to back off
    a tiny bit, but not much.

    Since it's a teleconverter and not a teleextender, there will be very
    little light fall-off. The C-210 isn't a very large diameter so there
    will be some, but the B-300 and TCON-17 converters which give 1.7x have
    no measurable light fall-off..
     
    Charlie Dilks, Oct 28, 2003
    #4
  5. Losing a stop means a halving of the light; ie. going from f 5.6 to f 8.
    As to your original question, a 1.9x teleconverter would make a 4 foot
    pole look 7.6 feet tall at the same distance.
     
    Charlie Dilks, Oct 28, 2003
    #5
  6. Freedom

    Rob Wild Guest

    Correct (basic) exposure is determined by three factors:
    Film Speed (ISO or ASA)
    Aperature (F/#)
    Shutter Speed (1/250th sec)

    The difference between each measurement is 1 stop. Each stop of
    difference means that there is either double (going up) or half (going
    down) as much light hitting the film/sensor

    ie:
    ISO 100 +1 stop = ISO 200 (twice as fast or sensitive)
    F/11 +1 stop = F8 (F8 is a larger aperature, so it lets in more light)
    1/125 +1 stop = 1/250th sec (twice as fact

    Hence in my previous post whereby you may lose about 2 stops, the
    teleconverter may alter the correct exposure calculation as follows:

    (Without) E(exposure) = ISO200 @ F/11 @ 1/125th sec
    (With) E(exposure) = ISO200 @ F/11 @ 1/30th sec (OR)
    (With) E(exposure) = ISO200 @ F/5.6 @ 1/125th sec.

    Real-life example...

    (A guess) Am shooting at a person 12ft away with a 80mm lens. I will
    most likely see the person's head, shoulders, maybe most of their torso.
    Adding the teleconverter, same person, same distance away, with an
    effective focal length of 152mm, the person's head is likely to fill the
    frame. I may be able to get in a shoulding, depending on composition,
    but the head will be predominant in the frame.

    cheers

    Rob
     
    Rob Wild, Oct 28, 2003
    #6
  7. Freedom

    Rob Wild Guest

    Charlie Dilks wrote:
    Charlie,

    Pardon my ignorance, but what is the difference between a teleconverter
    and a teleextender? I also thought that it was a general rule-of-thumb
    that there was a light falloff equiv to the focal length multiplier?

    cheers

    Rob
     
    Rob Wild, Oct 28, 2003
    #7
  8. A teleconverter goes on the front of the lens. A teleextender goes
    between the lens and camera. With a TE there is an equivalent light
    falloff. With a TE it depends on the diameter. With the huge diameter of
    the b-300 and TCON-17 relative to the lenses they're mounted on there is
    no light falloff.

    "Oly claims that the B-300 requires no exposure correction on the IS-3,
    and the same appears to be true on the digital side."
    From:
    http://www.cliffshade.com/dpfwiw/c-2000z/lenses/index.htm#b-300
     
    Charlie Dilks, Oct 28, 2003
    #8
  9. I meant, "With a TC (teleconverter) it depends on the diameter, not TE..
     
    Charlie Dilks, Oct 28, 2003
    #9
  10. Freedom

    Rob Wild Guest

    Many thanks Charlie,

    have not actually seen one of those before - have only seen the ones for
    between lens & camera - ie: Canon's 1.4x & 2x.

    cheers

    Rob
     
    Rob Wild, Oct 28, 2003
    #10
  11. You won't loose any stops with "Olympus type" teleconverter - a
    teleconverter that attaches to the front of the lens. The trade off is
    that with this type of teleconverter you cannot change the focal length
    of the main lens, meaning that it should always stay at its maximum
    focal length.

    The "traditional" teleconverter that goes between the lens and the body
    lets you use the entire range of focal lengths if the main lens, but you
    have to pay for this convenience with lost stops.
     
    Andrey Tarasevich, Oct 28, 2003
    #11
  12. This sounds great to me......You just screw it onto the front of your lens
    like a filter, and it increases the focal length without making the lens any
    slower? - Sounds like something every manufacturer should sell as an
    auxilliary to all their long lenses.....It must distort the image in some
    way, or everyone would use them.....A 100mm Nikor f2.8 sells for under $100
    (E type) A 200mm f2.8 Nikor sells for over $500....But I can get this simply
    by adding one of these magic filters........And, (I suppose) you could stack
    two or more of them........
     
    William Graham, Oct 28, 2003
    #12
  13. Well, you should probably suggest that to the manufacturers.
    Of course it must, as any teleconverter. The lens was designed to
    perform best without it. There's no way to achieve the optimal result
    under these circumstances.
    It would be interesting to know where you got the idea that a cheap
    100mm lens with a teleconverter can perform as well as a dedicated 200mm
    lens. Sounds like you have a great experience with "magic" teleconverters.

    As for calling "external" teleconverters "filters" and suggesting to
    "stack" them... you obviously have never seen one.
     
    Andrey Tarasevich, Oct 28, 2003
    #13
  14. There is also another trade off - putting a [frontmounted] teleconverter in front
    of your lens means close focus will be affected, much in the same way as lens
    speed is affected with a "traditional" teleextender/-converter that is inserted
    between the lens and the camera body.

    Regards,

    Per Nordenberg
     
    Per Nordenberg, Oct 28, 2003
    #14
  15. This is because frontmounted teleconverters (unlike those traditional converters
    that goes between the lens and the camera) are working according to the 'Galileo
    telescope principle'.


    Regards,

    Per Nordenberg
     
    Per Nordenberg, Oct 28, 2003
    #15
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