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Actually I'm planning to buy multiple lens but my budget is little less I can't afford telephoto Lens so if I buy tele converter, is it possible that I can use it for all types of lens or only for specific lens

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  • A teleconverter is basically a magnifying lens used between the camera body and the existing lens, it is also called an Extender.

  • Physical compatibility with a teleconverter depends on the lens being used and not the camera, but of course they need to be the same mount. A lens with a protruding rear element, which would mesh with the teleconverter front element, cannot be used.

    In general wide angle lenses cannot be used due to protruding rear elements.

  • A 1.4x extender will cause your maximum aperture to be reduced by one stop, a 1.7x extender causes a one and a half stop decrease, and a 2x extender results in a 2 stop loss of light.

    A simple means to calculate your resulting F number is to multiply the Teleconverter's magnification by the lens' F number.

  • The autofocus Teleconverters will not allow autofocusing less than f /5.6, the general rule to follow is lenses with a maximum aperture slower than f/ 2.8 can not be used with a teleconverter. Manual focusing is still possible.

    Some newer camera bodies offer f/8 autofocus, meaning that an f/4 lens with a 2X teleconverter attached (2 stops of light lost) will still allow autofocusing.

    It's probably best to buy a lens Teleconverter of the same brand as your lens so you can check the manufacturer's website for compatibility and to avoid warranty issues.

  • You want to spend a fair bit on a quality Teleconverter since it will affect the quality of the images produced by the lens it is used with; expect reduced sharpness in any event.

    If you have a large lens collection one expensive extender can double your lens choices. If you have a small and inexpensive lens collection a moderate priced extender might be more budget conscious.

  • Usually they are available in 1.4 to 2x magnification, with prices ranging from U$50 to over U$2K.

  • Some lenses include an extender and it's possible to stack multiple extenders and get an acceptable result at a much lower cost and weight than an equivalent super telephoto lens.

    Canon has a Japanese patent for a 400mm lens with with a 2 stage extender allowing both 1.4 and 1.7 multiplication. Whether it will come to market remains to be seen.


The advantages an extender gives you:

  • A longer focal length (obviously)
  • A better focal length/weight ratio
  • A better focal length/price ratio (there are some exceptions)
  • Double the compositional options
  • A way to get to focal lengths that aren’t achievable with a prime lens on its own
  • Shorter overall length when used with a long focal length lens
  • Since you're only using the center of your lens any vignetting will be reduced

The disadvantages of using an extender are:

  • Reduces AF tracking speed and accuracy
  • Increases chromatic aberrations
  • Decreases lens sharpness
  • Decreases image contrast
  • Since you're magnifying the central portion of your lens any flaws are magnified, so the quality of the lens being extended plays a greater role than the quality of the extender itself, though it's still important.

Further reading: See Dan Carr's article, The Ultimate Guide to Extenders or Teleconverters.

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    "1X of magnification" is no magnification at all.... – mattdm Dec 4 '17 at 5:49
  • It's one stop per 1x, there's no suggestion that the size 1x is available. – Rob Dec 4 '17 at 6:08
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    @Rob It's one stop per 1.4X of magnification. – Michael C Dec 4 '17 at 10:42
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    To be real pedantic it's one stop for √2 magnification. – Aram Hăvărneanu Dec 4 '17 at 12:01
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    @ben rudgers - Added both comments, and a load more. Probably coming back for some tweaks. Hopefully it's close to a complete answer now. – Rob Dec 4 '17 at 18:31
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Teleconverters can only be used with specific lenses.

Issues of fitment with the modified mount prevent them being used with Canon EF-S lenses. Even with EF lenses or third party APS-C only lenses where the mounts would couple, the arrangement of the rear lens elements in many lenses prevent them from being attached to teleconverters due to clearance issues. Elements of the TC and rear elements of the lens would collide before the lens and TC could be attached at the mounts.

In general, for Canon extenders (Canon calls them extenders rather than teleconverters), those lenses able to accept extenders are 135mm or longer telephoto prime lenses or the 70-200mm family of zoom lenses along with the 100-400mm series from Canon. Those aren't exactly budget lenses. Even then, using a TC to get more 'reach' comes with tradeoffs that you may or may not be willing to make.

  • A 1.4X TC costs you one stop of aperture, a 2X TC costs you two stops.
  • When your 150-600 f/5-6.3 becomes a 210-840mm f/7.1-9 your camera will no longer autofocus. Putting a 2X TC on an f/4 lens will disable AF unless you are using a Canon 1D X, 1D X Mark II, 5D Mark IV, 7D Mark II, or similar camera with some AF points that function at f/8. Ditto with a 1.4X on an f/5.6 lens. Most Canon DSLRs including all of the Rebels are designed to autofocus only with lenses with a maximum aperture of f/5.6 or wider (lower f-number). To retain AF with cameras that limit AF to f/5.6 or wider: with a 1.4X you need an f/4 or wider constant aperture lens. For a 2X you need an f/2.8 or wider lens.
  • Image quality can take a hit because all of the optical flaws of your lens are magnified. You'll probably see less sharpness and contrast and more CA and flare.
  • AF Speed will probably be slower and less consistent if it works at all.

Some third party teleconverters will allow you to mount wider lenses than the telephoto lenses on Canon's compatibility list. But they don't make much sense. For about the same price of a decent quality TC, one could just buy a 55-250mm f/4-5.6 lens that would produce better image quality at better maximum apertures rather than trying to use a 2X TC with your 18-55mm or 18-135mm kit lens. That's why TCs are designed to work with telephoto lenses. Only when the expense of a long telephoto comes into play does a high quality TC priced at a very small fraction of the price of such a lens make it a "budget" option.

Take for example the Canon EF 70-200mm f/2.8 L IS II. It is a $1,900 lens. Put a $450 EX 2X III between it and the camera and you have a 140-400mm f/5.6 lens that is pretty close in terms of optical quality to the Canon EF 400mm f/5.6 L for less than half the cost of the 400mm f/5.6 prime ($1,150).

  • EF 70-200mm f/2.8 L IS II + EF 2X III = 140-400mm f/5.6 for $2,350
  • EF 70-200mm f/2.8 L IS II + EF 400mm f/5.6 L = $3,050

This goes even further when looking at extending Super Telephoto lenses:

  • EF 300mm f/2.8 L IS II ($6,100) + EF 2X III ($450) = 600mm f/5.6 for $6,550
  • EF 300mm f/2.8 L IS II ($6,100) + EF 600mm f/4 L IS II ($11500) = $17,600

or

  • EF 300mm f/2.8 L IS II ($6,100) + EF 1.4X III ($450) = 420mm f/4 for $6,550
  • EF 300mm f/2.8 L IS II ($6,100) + EF 400mm f/4 DO IS II ($6,900) = $13,000

For the $6,100 cost of the EF 300mm f/2.8 L IS II and both the EF 1.4X III and the EF 2X III at $450 each one would spend $7,000.

For the EF 300mm f/2.8 L IS II, The EF 400mm f/4 DO IS II, and the EF 600mm f/4 L IS II one would spend $24,500.

Budget lenses, even telephoto ones, don't do very well with teleconverters. This is because the TC magnifies all of the faults of the lens' center projection.

You do get the benefit that defects on the edge of the field are cropped out, but the loss of sharpness and contrast combined with the increase in flaring and chromatic aberration are usually noticeable enough that a budget telephoto lens at the same power is optically better.

This is particularly the case if one is willing to accept the limitations of a reflex mirror lens in the 500m to 800mm range. Even apart from mirror lenses, there are now several options for 150-600mm f/5-6.3 for only a little more than $1,000. Compared to the prices of Canon and Nikon Super Telephoto lenses beyond 300mm, that $1,100-$1,300 price tag is extremely low.

If that is still beyond the reach of one's budget, a "superzoom" fixed lens camera is even more affordable. Although such "superzooms" have smaller sensors, the optical quality of their lenses combined with good lighting conditions will often allow then to outperform an APS-C DSLR with a cheap telephoto lens and a cheap TC attached.

For further reading please see the following questions here at Photo Stack Exchange:
Can I use an Canon 2x Extender on my EF-S 18-135mm lens?
Will a Sigma 1.4tc teleconverter work with my Canon 70D?
Are there any Teleconverters/Extenders which will work with a Canon Rebel EOS T3 and 55-250mm f/4-5.6 lens?
How does a teleconvertor affect magnification ratio?
Will the Canon 5D MK II with 100-400 1:4.5-5.6 work properly with Kenko 1.4 converter?
How do I choose a teleconverter for my Tamron 70-200 f2.8 and Canon camera?
Does a full frame with a teleconverter perform better than an APS-C without a teleconverter?
Will I not be able to AF with a 2× teleconverter?

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