 BetterPhoto Member |
tele-extender question I recently purchased the Canon 75-300 mm IS zoom lens and want to know if I can buy a 1.4 or 2X tele-extender for it that will maintai all it's features, auto-focus etc.? From Canon's description it doesn't appear that the extenders will not work with this lens, is that true? Thanks
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Dave Cross |
Hi Ralph. Tele-extenders reduce the amount of light available for the auto-focus system to use, this leads to focus hunting (going from close to infinity focus repeatedly without locking). To prevent this Canon disable the autofocus when an extender is in use. You CAN make the autofocus work by applying tape to some of the lens contacts (don't remember which ones just now, Google should help), obviously you will need good light to prevent the hunting problem. There is also an issue with certain extenders and certain lenses (particularly Canon back focus telephotos) actually fitting together. So take the lens you want to use along to the shop to ensure it fits. Hope this helps. Cheers
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Jon Close |
Canon's own teleconverters EF 1.4x and EF 2x will not fit on the EF 75-300 f/4-5.6 IS, or most other lenses. They have an extended front element that will interfere with that lens's rear element. The Canon teleconverters can only be mounted to a select few Canon L-series telephoto lenses. When connected to these lenses, the Canon TCs electronically convert the aperture signal from the lens so that the camera displays the effective aperture, eg. with the EF 2x on a 70-200 f/2.8L, the maximum aperture displayed by the camera is f/5.6. These TCs will also slow or disable AF when the effective aperture is f/5.6 or smaller. You can use a third party TC, such as Kenko or Tamron, with your lens. These TCs have a recessed front element so they should mount without trouble. They also have less sophisticated electronics and just just pass through the lens/camera communications. The camera does not know that the TC is present, and will display the aperture without conversion. No big deal as it will meter correctly. Similarly, it will attempt to autofocus, and may work in bright light or on high contrast subjects, but generally AF will not be reliable as the effective maximum aperture will be smaller than f/5.6. Sigma's APO TCs are a similar design to Canon's with extended front elements and are also limited to use only with a few of Sigma's EX and Canon's L telephotos.
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Jon Close |
Oh, P.S. I'm not 100% positive, but I'm believe IS feature will work with 3rd party TCs.
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