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I was wondering if A tele converter would be any good for my 18-200mm.
How much would it in crease the distance and what kind of distortion could you expect,
Thanks in advance,,Aidan,,
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That's the short answer at least
Simply put the 18-200mm lenses cover a massive zoom range, by 200mm the lens is already suffering from a softer overall clarity. If you put a teleconverter onto the lens its going to magnify those errors a lot more. Further teleconverters reduce the effective aperture of the lens itself. Chances are you're already close to f5.6 at 200mm already; a 1.4TC would lose you one whole stop and on Canon that means no AF (and even on Nikon where you keep AF you'll notice it drop a lot in accuracy and speed).
A 1.4TC would increase the lenses focal length by 1.4 times, but it honestly would really only be any good for record shots. Most people would simply be unhappy with the results.
A 2*TC would double the focal length, but takes away 2 whole stops of light and would give you very soft results (in fact the only zoom most people will use a 2*TC on is a new 70-200mm f2.8 IS L MII or VRII from Canon/Nikon)
There is also the issue that pretty much all teleconverters have a protruding front element. You certainly wouldn't be able to fit a Canon TC nor a Nikon one to the lens (depending on if you're canon/nikon/other). I'd guess that even a Kenko pro brand teleconverter (which are good) which has the smallest front element protrusion would still have problems mounting to that lens (from what I've seen 18-200mm tend to push back quite a bit).
If you want you could consider a 70-300mm zoom, that would give you better image quality and the budget options on the market are likely going to cost you just as much if not a bit less than a teleconverter would.
The other option is to look a little higher for something like a Sigma 120-400mm zoom lens.
After that you're going to have to save a bit longer and start thinking about the £1K price point - Canon having a 300mm f4, 400mm f5.6, 100-400mm; Nikon having a 300mm f4; Sigma making a range of 150-500mm and 50-500mm zooms.
I recently bought a Sigma 1.4 TC for my Sigma 70-200 f2.8 zoom. As Overread says its not worth it unless you've got a fast lens to begin with. My lens becomes a f4 with the TC attached and even then you need a bright day either that or ramp up the ISO. I don't expect to have to use the TC a lot but for the odd time when i need it it can be very usefull as proved when i tried to use the zoom to take a picture of a bird before i had the TC. I had to crop the picture a lot with the corresponding loss in quality. Also i didn't want to carry a big heavy 300 or 400 mm lens around with me.
I part disagree with the "not worth it brigade - with a 1.4x converter.
With a 2x AF does not work and the viewfinder is very dark - my advice is forget a 2x with this lens.
If your camera is a Nikon AF with a Kenko 1.4x works acceptably well with static subjects, and quality with the zoom at f8-11 is often good for an A4 print.
You have to hold the camera extra steady, and to accept AF may not work in low light.
Results will generally be better than cropping and at less cost than buying a lens that goes to 300mm.
Geat a cheap 3rd party 70-300mm lens for the same price as a good 1.4tc, for better results than putting a tc on the lens you have. If 300mm is enough.
Then you wont be bumping iso up to compensate the tc, therefore cleaner images and a little more room for cropping. Af will be faster and more accurate.
Totally agree with Gareth, converter on 18-200mm is a waste of time.
Quote: Totally agree with Gareth, converter on 18-200mm is a waste of time.
This is true, but more so for a full frame camera. On a crop sensor a 200 is effectively 320mm and with a 1.4 TC it takes it to 448mm. I used a 2x teleconverter on a rather slow 70-210 f5.6 in the days of film. It was very difficult to manually focus as the viewfinder was very dark. With my 1.4 on my Sigma it certainly takes longer to autofocus and can "hunt" a little but the results are ok and the viewfinder is not much darker, hence why i said a fast lens is initially required.
Generally its not worth bothering to try using either a 1.4x or 2x converters on a lens more than f2.8 aperture... then again it depends on what you are shooting...available light... camera body (crop frame) etc etc...
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