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Old Feb 11, 2004, 11:38 PM   #1
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Default TC's and non-supported lenses

I know that Canon only recommends certain lenses to be used with their TC's, but what happens if you install a 1.4X TC with a Canon lens not on the supported list?
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Old Feb 12, 2004, 12:05 AM   #2
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I use a tamron 2x with the canon 100-300usm and it works BUT
the camera will not focus well when the lense is slower than f5.6.

You loose 2 stops of light with a 2x, 1 stop with the 1.4x.
With this combo it is usually manual focus or autofocus in very bright light.
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Old Feb 12, 2004, 12:23 AM   #3
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The canon TCs protrude into the lens you're attaching it to. Therefore, the lens needs to have enough room to accomodate the TC. Only 'L" lenses have that room.

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Old Feb 12, 2004, 1:06 AM   #4
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Peter, yes I understand the focusing at f stops > 5.6 but I was looking for things mechanical or anything that would prevent the operation at all from the Canon TC. Thanks though.

Thanks Barthold. That's what I was trying to find out. Mechanical problem. (although I have heard from a VERY reliable source that you can use a TC if you put an extension tube between the two. Your explaination would make sense then.
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Old Feb 12, 2004, 6:27 AM   #5
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Quote:
Originally Posted by barthold
The canon TCs protrude into the lens you're attaching it to. Therefore, the lens needs to have enough room to accomodate the TC. Only 'L" lenses have that room.
Not all "L"... my 85mm f/1.2L is an example (or the 50mm f/1.0L), although they would be great combinations!

Doesn't it vignette with an extender if the lens is not long enough though (and limit the range on the AF)?
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Old Feb 12, 2004, 9:14 AM   #6
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I was just going to suggest the extention tube to get around the problem. Not the best solution, but if you really need the TC, it will work.

Another option is to use another company's TC. I know this works with Nikon, I assume with Canon. I expect it's because they don't protrude as much, and therefor don't hit the first/last lens element. But I don't know if the clearance is enough on the Canon lenses.

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Old Feb 12, 2004, 9:58 AM   #7
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Well, it's not so much as a "need" to use it with other lenses as that I have the TC and I have other lenses that aren't on the list and I was just wondering "why". You know....enquiring minds and all that 8)
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Old Feb 12, 2004, 10:07 AM   #8
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Using an extender in between the TC and the lense, Ah do believe you loose ability to focus at infinity, and you also loose a bit more light.

Quote:
Originally Posted by NHL
Doesn't it vignette with an extender if the lens is not long enough though (and limit the range on the AF)?
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Old Feb 12, 2004, 10:26 AM   #9
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I've read posts of people that use Sigma TCs on Canon non L lenses. Never tried it myself, thus if you really need this better verify it first.

NHL, it seems that the TCs are made for long lenses anyway. Using a 1.4 TC on my 70-200L IS results in images I can live with, but I can see the difference. Maybe I'm too picky...

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Old Feb 13, 2004, 10:41 AM   #10
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The Kenko pro line of TCs state that using them on lenses shorter than 100mm will be detrimental to the image.

I think the problem with lenses wider than 100mm is that they have an additional 'reverse telephoto' lens grouping at the back of the lens because of the space between the lens back and the film/sensor plane. I've seen this as an explanation as to why SLR lenses are much larger than rangefinder lenses.

I think that the TC ruins the optics that the wide angle lenses need.

Adding extension before a TC would act to eliminate infinity/long distance focus but would give you the abilty to focus closer than normal. You will lose light but the camera is metering through the lens so it would expose properly - using a hand-held light meter would require some experimenting.

If you can get it - John Shaw's 'Close Ups in Nature' has a good discussion of extension with TC's and zoom lenses.
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