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Old Dec 21, 2006, 9:26 PM   #1
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Still shopping for my dslr, but TC keeps coming up in the forums and I don't really know what it is, or what it will do for me. Just trying to fill in the peaces. Thanks for your help!

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Old Dec 22, 2006, 12:14 PM   #2
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A teleconverter is an optical appliance that goes between the camera and a lens to optically extend the focal length. Example the Nikon TC-14E 11 They come in 1.4x, 1.7x and 2.0x flavours.

It works by magnifying the center of the image with a corresponding loss of light. A 1.4x makes a 300mm look like a 420mm but with the loss of one stop, a f/2.8 becomes an f/4.
A 1.7x makes the 300mm look like a a 510mm with the loss of one and a half stops while a 2x makes the 300mm look like a 600mm with a two stop loss.

There is no free lunch though. Because they work by magnifying the center of the image they will degrade the image quality as the magnification increases. The loss of light may also cause autofocus failures. They are really meant to be used with professional grade prime telephoto lenses that are fast to begin with. Using them with consumer grade telephoto zoom lenses may give unpredictable results.


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Old Dec 22, 2006, 12:52 PM   #3
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Bob's answers are dead on. One other thing to note: most consumer level DSLRs only have autofocus if a lens has f5.6 available. What this means is: if you are using a consumer grade telephoto lens that has a max aperture of 5.6 and you slap a TC on it, you are likely to lose autofocus (you'll also lose autofocus by slapping a 2.0 TC on an F4 lens since that converts the lens to 2.8).

Now, having said that, the autofocus loss only occurs when the camera KNOWS the lens doesn't have 5.6 available. The camera KNOWS this because of communication that occurs betwen the two via pins in the lens or TC (which match up to receptors on the camera body). Normally, available aperture is communicated all the time. But, certain 3rd party TCs do not communicate this information. So, if you use one of the third party TCs you may retain autofocus. But, you'll still have issues - autofocus will be slower and may not work at all as light levels drop.

So, bottom line - Stick with Bob's advice - unless you're buying pro level telephoto lenses that are f2.8 or f4.0 throughout their zoom, stay away from the TCs.
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Old Dec 22, 2006, 3:01 PM   #4
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I agree with everything Bob and John have said with one exception. If you do have a quality pro level lens and you get a quality pro level TC there is little if any image quality degredation.
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Old Dec 22, 2006, 3:31 PM   #5
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I wanted to clarify caboose's answer a bit.
A TC magnifies the center of the lens. this is normally the optically best part of the lens, but you get what you pay for. Lower quality lenses are fairly good without a TC added, but when you add one their flaws are readily apparent. This is because they have been magnified!

This is why some lenses cost so much money. I own the Canon 600mm f4 IS lens. It is absolutely stunning... amazing. And hugely expensive ($7200 USD.) And part of what makes it worth it is if I put a 1.4xTC on it, you can't tell the difference... there is really no quality loss what so ever. If you add a 2xTC you will see some optical quality loss, but not tons.

Since you're shopping around, I would suggest you not really consider a TC for a little bit. It probably won't save you money (I know of no package deals that include TCs) so think about what focal length you want and buy some lenses that cover that. Then, when you've been shooting for awhile and know what your setup does or doesn't do... then consider more stuff, like a TC, or a macro lens, or an extention tube, or another lens, or a flash,....

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Old Dec 22, 2006, 4:22 PM   #6
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You all are awesome! Thank you for your help. I'm finally figuring out the lens thing (somewhat) and really don't want to add anything else to my already over loaded brain. Appreciate you help.

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Old Dec 25, 2006, 10:29 AM   #7
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eric s wrote:
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This is why some lenses cost so much money. I own the Canon 600mm f4 IS lens. It is absolutely stunning... amazing. And hugely expensive ($7200 USD.)
Eric
If only I lived in the USA, over the pond in the UK this lens costs £5790.00 which at todays rate is $11,423. Which is 5,000 reasons why I do not have it

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Old Dec 26, 2006, 9:37 AM   #8
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Oh, my god. I wouldn't own it at that price either! That is absolutely crazy.

When I purchased it, I got it because I needed it (I photograph wildlife in an area where wildlife doesn't come close to you.) After looking at the results the first day, I thought "damn, this is a really good lens..." and I've been happy I got it (except for the weight) ever since.

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Old Dec 26, 2006, 10:06 AM   #9
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eric s wrote:
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Oh, my god. I wouldn't own it at that price either! That is absolutely crazy.

When I purchased it, I got it because I needed it (I photograph wildlife in an area where wildlife doesn't come close to you.) After looking at the results the first day, I thought "darn, this is a really good lens..." and I've been happy I got it (except for the weight) ever since.

Eric
Yes exactly I wouldn't own one as well, but I am sure it is wonderfull lens and I am glad that you could afford it, I only do this as a hobby so I do not sell any pictures, therefore I have no means of recovering such a vast sum however I do own several 2.8 L zooms the longest been my 100-400mm which I adore, I even stack it with my EF 1.4 plus EF2 both canon which gives me 1792 on my 20D ( if my math is ok ) I use this set up on tripod with mirror locked up and fired by remote in order to photograph the moon, and I still can't see where you guys landed :G

Happy xmas and have a good new year

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