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Thread: Teleconverter / extension tube

  1. #1
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    Teleconverter / extension tube

    Hello everyone...

    I'm a bit confused with teleconverter & extension tube.
    Are they the same thing?
    What are the purpose of having them on your lens?
    Because some of the genuine teleconverters are quite expensive.

    Very grateful to have insights from the experience.

  2. #2

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    Re: Teleconverter / extension tube

    Put simply, the two are very different.

    Teleconverter
    Basically a magnifying glass in a holder that fits between the lens and camera. Used to make the focal length of a lens appear to be longer than it is. They come in different "strengths", from 1.4x through 1.7x to 2x or even more.
    Used with a short telephoto lens, say a 135mm f/3.5, the 2x would "turn it into" a 270mm lens, so things wuld appear bigger. It would make the fastest aperture f/7 though, so unless you start with expensive lenses they force you to use slow apertures.

    Extension tubes
    Sinilare looking, but hollow. There is nothing inside the extension tubes, they are just, well, extension tubes.
    Focusing the lens on the camera moves the glass bits away from the film/sensor as you focus on something closer until you hit the stop. At the point where there is no movement left on the focus adjustment you are the point of closest focus. Enter the extension tube. Fit this between the lens and camera and you can then move the glass bits even further away from the film/sensor, so you can focus on sloser things than before. You can't however focus on distant things anymore as you can no longer move the glass bits far enough towards the film/sensor. They usually come in sets so that you can pick how much extension you need and use one or more tubes to acheive focus.

  3. #3

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    Re: Teleconverter / extension tube

    Just to add a bit to Jonathan's reply and add some warnings.

    Teleconverters need to be used with care. Adding that extra glass will produce a poorer image and you may lose autofoucs. I say may because there are a lot of variables here. A 1.4x converter used with a good quality prime lens will still produce acceptable results but when added to a cheap zoom it usually gives disappointing images.

    A 2x converter is even worse, but can be acceptable when used with a top notch lens, say something over 1000.

    Some lenses will not accept some converters. The Canon converters, for instance, will only fit on selected lenses.

    Extension tubes are mostly used for macro work where you need to get closer to the subject, which will give a larger image. Because they don't contain any glass there is no degredation of the image but they do 'soak up' quite a lot of light so you will probably have to alter your exposure or ISO to suit. The longer the tube the more this will be a problem.

    I often use a 25mm tube for macro work which gives me around 1 ft of closer to subject distance, variable depending on lens. I find that the camera readings can sometimes be false but usually consistant so a bit of trial and error will overcome any difficulties.

    In both cases, genuine products are expensive. Expect to pay upto 100 for a 25mm tube and 250 or more for a teleconverter. Very cheap options are not recommended.

    If you can supply more details of your camera and lenses plus some idea of what you wish to achive I am sure somebody will be able to give a more precise answer.

    It can be a complicated subject, so hope this helps a little.

    Geoff.

  4. #4

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    Re: Teleconverter / extension tube

    Quote Originally Posted by Geoff F View Post

    A 2x converter is even worse, but can be acceptable when used with a top notch lens, say something over 1000.
    I'd pretty much agree with this. I think a big part of the problem is that a LOT of images I see are "sub-optimally sharpened", and yet with a 2x teleconverter sharpening is not only needed more, there's also less margin for error -- but it can be done.

    Here's a 100% crop from an EF70-200mm F2.8L IS USM with a TC2.0 ...

    Teleconverter / extension tube

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