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Old Sep 29, 2006, 11:03 AM   #11
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Here are a few more examples. These were all taken at 420mm (300x1.4x). Poor lighting but you can see the images are sharp.

http://www.stevesforums.com/forums/v...mp;forum_id=11

The lighting in this one was a better.

http://www.stevesforums.com/forums/v...mp;forum_id=11
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Old Sep 29, 2006, 1:33 PM   #12
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leeraff wrote:
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Please explain teleconverters. How they work. Different situations, etc.

Assume from "tele" they may help extend the reach of a particular lens. Please explain with any relevant examples.

Thanks!
OK,

Sorry if you already know this but I'll state it anyway since I didn't see it explicitly called out in any other responses -

A 1.4x TC turns a 70-200mm lens into a 98-280mm lens (70x1.4 to 200 x 1.4). Then, you can add the camera's crop factor on top of that. So that 70-200mm lens with a 1.4x TC on a 30d (which has a 1.6 crop factor) now behaves like a 156.8 - 448mm lens.

A 2x TC works the same way accept multiply by 2 instead of 1.4.

As others called out, a 1.4x reduces the max aperture of a lens by 1 stop. So a 2.8 lens would only be capable of f4.0. A 2x TC reduces the max aperture by 2 stops - so that 2.8 lens now works like a 5.6 lens. And, here's the kicker - Canon's consumer level cameras (non 1 series) cannot autofocus if the lens has a lower max aperture than 5.6. You either have to manually focus such lenses, or use a TC that does not communicate aperture information to the camera body (some TCs do not and others you could tape the communication pins that communicate this data). However, realize that however you trick the camera, a lens that is only f8 or narrower is going to have a tough time focusing.

Also, as others have mentioned you reall want to start with a great quality lens if you're going to use a TC. Throwing a 2x TC on a $150 70-300mm 5.6 lens is probably not going to yield very sharp results.


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Old Sep 29, 2006, 2:38 PM   #13
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I guess it is common sense to buy a good product to get good results, but what are the good 1.4x and 2.0x teleconverters for Canon lenses? Is there a site where they have been listed and tested?
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Old Sep 29, 2006, 3:21 PM   #14
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One other point I did not see mentioned so far.
TC's come in 2 flavours, there are generic TC's and matched TC's.

The generic TC's do not cost much in cash, fit any lens but are not good optically.

The matched TC's like those from Canon and Sigma are made specifically for the Canon L and Sigma EX lens lines, and they are not cheap. Optically they are very good.

I started off with the Sigma 2x TC first, then added a 1.4 TC to the bag.

If you want to really push it you can stack a 2x and a 1.4x to turn a 300 F2.8 into an 840mm F8 lens.

Works out to 1344mm effective on a 1.6 crop camera like the 30D or 400D :idea:, but don't expect much in the way of image quality. :? And the 30d/400d will not autofocus at F8, a 1d will.
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Old Sep 29, 2006, 3:27 PM   #15
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There are only 2 makers of matched Tele-converters for Canon lenses.
Canon and Sigma, they are interchangable.

Canon's are white, Sigma's are black, Just a matter of estethitics on which color you want to match your lenses. :G

The matched teleconverters can only be used on appropriate Canon L or Sigma EX lenses.


harana wrote:
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I guess it is common sense to buy a good product to get good results, but what are the good 1.4x and 2.0x teleconverters for Canon lenses? Is there a site where they have been listed and tested?
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Old Sep 29, 2006, 3:28 PM   #16
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I'm not completely sure about this but in the case of Canon TC's don't you have to use MKI TCs in order to stack, or maybe one MKI and one MKII? I don't think you can stack the MKII's.

Not sure if it was pointed out but the AF also suffers a little when a TC is used.. its not quite as fast.
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Old Sep 29, 2006, 3:33 PM   #17
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The older Canon TC's needed a spacer between them to stack, aparently the new version no longer needs the spacer.

Sigma's could stack out of the box.

Yes the less light the slower the AF, until firmware stops it altogether somewhere around F5.6 on the 30D/400D.
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Old Sep 29, 2006, 3:35 PM   #18
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I won't say for sure until I find out but I'm fairly certain the II series will not stack. The rear is flush and the front protrudes, at least on my 1.4. I know the front of the 2x protrudes but can't say what the back is like. I guess if anything the 1.4 would have to go behind the 2x.
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Old Sep 29, 2006, 3:57 PM   #19
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Ok from searching the 1.4x II and 2x II can stack but the 1.4 has to go behind the 2x II. I guess the back of the 2x is recessed.
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Old Sep 29, 2006, 4:29 PM   #20
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Widowmaker wrote:
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I see no loss when using mine with my 300 2.8 IS and its tack sharp wide open.
You won't see any loss from an exposure perspective (brightness of the image), because the camera's metering is looking through the TC to determine the shutter speed needed to properly expose the image for the lighting and ISO speed you're using.

But, you're losing about 1 stop of available brightness with a 1.4x TC. The focal length is getting longer, and the aperture iris opening is staying the same. Since aperture is a ratio between the iris opening's area and the focal length of the lens, you're losing around half the light using a 1.4x TC.

Depending on the TC, it may or may not report the light loss (largest available aperture) and focal length change to the camera. But, it's there. Basically, your 300mm f/2.8 becomes a 420mm f/4 when using it from a shutter speed perpective (you'll get slower shutter speeds for the same lighting and ISO speed shooting with the aperture wide open with it, versus without it).

Likewise, the Autofocus Sensors see less light for focus purposes, and your viewinder receives less light. It may not be that noticeable to you. But, in very low light, it can make a difference.

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