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Old Jan 1, 2007, 7:55 PM   #1
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Looking to lengthen my 300mm lens for birding... thanks, Donna
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Old Jan 2, 2007, 12:35 AM   #2
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It depends on the make of your lens. A lot say get the same make of TC for the make of your lens cuz the TC would be more optimized for it. I had a Tamron 1.4x SP TC that worked in just about any lens you attach to it...but when I got a hold of a Canon 1.4x TC and compared its IQ when mounted w/ my 70-200 IS lens, the Canon TC yielded a slightly better IQ...slight...but still noticeable when you I pixell peeped...so I sold my Tamron.
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Old Jan 2, 2007, 8:51 AM   #3
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Also, don't forget if you go with Canon TC, you'll lose autofocus with your lens. Canon non 1 series DSLRs require a lens with 5.6 aperture to autofocus. A 1.4x TC causes you to lose 1 stop and a 2x TC causes you to lose 2 stops of aperture.

So, unless that lens is a 300mm f4 or 300mm 2.8, when you slap a Canon or Sigma TC on it you'll lose autofocus. Some other TCs (I can't remember which) do not report max aperture back to the camera so autofocus is still possible - although it may be very poor. You'll also see a degradation of IQ. TCs were designed for use with top quality telephotos in mind. So, you may want to seek reviews of folks that have used whatever lens you're using with a TC and find out how well it worked. Otherwise you may just end up wasting $$$ on a TC that would be better spent saving up for a longer lens.
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Old Jan 2, 2007, 9:56 AM   #4
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Well, I think I have already wasted my money...I bought a mint condition vivitar series one teleconverter. I spent about $80. I thought the series one was supposed to be good. Anyway, not a lot of money...Donna
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Old Jan 11, 2007, 12:48 PM   #5
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I'm still a little confused on the TC issue. If I understand, some lenses will lose AF and some will not?

I haverecently purchased a30D and was pondering a 70-200 f/2.8 for indoor gymnastics use (hoping it will be long enough) and thinking for my sons T-ball games that I could use a canon 1.4 TC and the added stop would not hurt me as I would be outside during the daytime. While I am showing my ignorance, if the lense is a 2.8, what is the next "stop" I would be relegated to? However, if I am going to lose AF, I may need to go another route.

Chris
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Old Jan 11, 2007, 1:03 PM   #6
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With a 1.4x TC on the 70-200 f2.8, your lens becomes f4. With a 2x TC, it becomes f5.6. You do not lose autofocus with either TC's...just make sure you get a good TC.
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Old Jan 11, 2007, 2:05 PM   #7
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With a lens like a 70-200 f/2.8 L the key is to get a matched high quality TC from the lenses manfacturer.

(Sigma EX and Canon EF TC's are interchangable, they just a different color)
They won't fit on lenses they were not meant for, the lens rear element needs to be rescesed for the TC front element to fit in.
They are not cheap.

Canon 1.4X TC http://www.bhphotovideo.com/bnh/cont...goryNavigation
Canon 2x TC http://www.bhphotovideo.com/bnh/cont...goryNavigation


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Old Jan 11, 2007, 8:39 PM   #8
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Thanks AlpineMan and PeterP! I found a chart on canon's website which gives the stops which their lenses will work at with a 1.4 and a 2.0 AND it tells more about the AF issues with each of their lenses as well.

I will probably go with a canon TC...and you're right, they are more expensive than I would have thought.

Thanks again guys.

Chris
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Old Jan 16, 2007, 3:57 PM   #9
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That's great!

The AF issue is not with the lens itself, but with the body it is on.

The firmware in the non-pro (read non 1D) bodies gives up trying to AF if it sees too slow a lens mounted. Somewhere around f/5.6-f/6.3 is about the limit. The 1D go to about f/8 before they too give up.

Unless you use the tape trick, where you tape over the contact that reports the aperture to the camera. Then you end up with a camera/lens that spends a lot of its time hunting for focus, and rarely finding it :G
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