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Old Jul 1, 2008, 4:27 AM   #1
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hi

Has anyone used (or is it possible) this 1.4x with a 70-300 is USM canon lens
http://www.warehouseexpress.com/prod...aspx?sku=12860


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Old Jul 1, 2008, 6:52 AM   #2
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Looks interesting, does the Canon TC fit between the camera body and the lens then? I have an oly TC (1.7) that I was going to try on the end of my 55 - 250mm lens, once the step up ring arrives, I figured it might be possible with manual focus?

Wonder how good that canon one is, found it here for around £160, might be worth considering as it would extend my lens to around 350mm, although that said my money might be better off going towards a bigger lens if needed.

http://www.onestop-digital.com/catal...products_id=55


Edit.. Or possibly the x 2, but wonder what sort ofimage distortion/vignetting you might get? Looks like they are designed for the L Series so not sure if compatible tho.

http://www.onestop-digital.com/catal...products_id=56
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Old Jul 1, 2008, 7:06 AM   #3
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simonbratt99

Note the compatibility chart on the same page as your link if you click on the Further Details tab:

http://www.warehouseexpress.com/prod...=12860#details

Camera manufacturers TCs are only designed to work with a very limited number of their brighter lenses because of light loss through a TC. You lose 1 stop of light (only half the light gets through) with a 1.4x TC, and you lose 2 stops of light (only 1/4 the light gets through) with a 2x TC.

Even if you could get one to mount without optical element clearance issues (which can be an issue with some designs), you'd probably lose Autofocus.

When you use a 1.4x TC, you lose 1 stop of light (only half the light gets through). So, a 70-300mm f/4-5.6 lens would become a 98-420mm f/5.6-f8

Most cameras will refuse to Autofocus once you get much dimmer than around f/6.3 or f/6.7 if a TC is reporting corrected Aperture Information to the camera.

Some third party TCs do not report the corrected Aperture to the camera. So, these can sometimes be used with a lens that dim. But, your camera may struggle to Autofocus in less than optimum lighting (because not as much light gets through to the camera's Autofocus sensors).


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Old Jul 1, 2008, 8:56 AM   #4
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thanks Jim,

So a multiplier is pretty much a no no with a non L series canon lens really?
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Old Jul 1, 2008, 9:18 AM   #5
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Some of the third party TCs can work. But, you'd need to make sure it's not one of the smarter ones with bult in electronics that passes corrected aperture and focal length to the camera, as they make both kinds (otherwise, the camera may refuse to even try to Autofocus). In some cases, you may be able to tape over some of the lens mount contacts to fool the camera into Autofocusing, depending on the camera mount (and I'm not that familiar with the way Canon passes information to and from lenses).

But, you'll have some amount of optical degradation using a TC, and you'll also have light loss (which means the AF sensors and viewfinder see a darker image). So, even if the camera attempts to Autofocus (which it probably will if the TC isn't reporting the corrected information), AF is going to be slower and will probably hunt a lot in less than optimum lighting.

A 1.4x TC is best used with a lens that can maintain an aperture of f/4 or brighter throughout the focal range, and a 2x TC is best used with an f/2.8 or brighter lens.

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Old Jul 1, 2008, 10:00 AM   #6
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See tip number 1 for the tape trick (which contacts to tape over). This would probably work on your camera, too (but, you'd have to try it to make sure).

http://www.fredmiranda.com/TipsPage/

But, you might have have optical element clearance issues trying to use a Canon TC with your lens (a problem that can occur with some designs). So, a third party TC (Tamron, Kenko, etc.) is a probably a better bet unless you know someone that's tried a specific TC with your lens (and perhaps one of forums members knows and will chime in).

But, optical quality isn't going to be as good with most third party TCs, and AF may hunt in less than optimum lighting, even if the camera does try to AF).

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