Tamron 2x teleconverter for Canon EOS EF lenses?

Discussion in 'Canon' started by Matt McKay, Oct 27, 2003.

  1. Matt McKay

    Matt McKay Guest

    Matt McKay, Oct 27, 2003
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  2. Matt McKay

    rarsin Guest

    That is a Kenko Teleplus MC7 (7-element, multi-coated) converter, re-badged
    as a Tamron. I used to own one. It provides pretty good performance for
    the price. It'll maintain autofocus when used with lenses f4.0 or faster.
    However, the Kenko Pro 300 series converters are much better, provide near
    equivalent performance to the Canon originals, at about half the price.

    More info at the Kenko web site:


    Cheers, Rab.
    rarsin, Oct 27, 2003
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  3. Matt McKay

    Matt McKay Guest

    How many AU$ for the 3x kenko? They don't have prices on their site...
    Anyone know?

    Also, I can get that Tamron 2x extender for US$50 + shipping for the US...
    What do you think? Should I go for it?
    Matt McKay, Oct 27, 2003
  4. For that price, I'd be inclined to - you could resell it on Ebay for
    more if you didn't want it... Want to get two and split the freight?

    Stuart Elflett, Oct 28, 2003
  5. Matt McKay

    PlaneGuy Guest

    Yes a two-stop loss is "quite common" for 2x converters. Actually it is the
    nature of the beast, here is why.

    For all intents and purposes a 2x converter takes the middle of the image
    that your lens creates, and magnifies it to fill the original image circle.
    Now a two times converter takes half the width, and half the height of the
    image, this then means one quarter the image area. By magnifiying the same
    amount of light as you get from the quarter image to a whole image, you
    decrease its intensity per unit area by four, or two stops. Hence a two stop
    loss of light.

    Now the 1.4 takes about 70% of the height and width, which means about half
    the area. Thus half the light which is one stop.

    Hope my simplistic explanation helps.
    PlaneGuy, Oct 28, 2003
  6. Matt McKay

    Ken Guest

    Thanks for the explanation PlaneGuy, I've known about the 2 stops, but never
    given thought as to why.

    Ken, Oct 28, 2003
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