teleconverter

are these any good? whats the best one for the best money? and do they do what they say on the box ? lol

TIA

Probably the Pentax one that has not appeared, as yet.

Not all TCs are compatible with all lenses, not even within the same brand of lenses, so a Sigma TC is not suitable for all Sigma lenses but will work with most Tamron or Pentax for instance. If you decide to buy one check lens compatibility first or you could seriously damage your lens.

You have to remember than a TC also makes the f stop smaller - so if your lens has a maximum aperture of 2.8 then with a 1.4 TC it is a stop smaller f4, and with a 2x TC two stops smaller, f5.6, making them only usable in good light. The smaller the aperture of the lens the less useful a TC is, at least in Northern Europe. For many zooms the maximum aperture at the long end is already 5.6 or 6.3, making a TC pretty useless unless you are in really really good light say in Africa, or Australia.

Elizabeth David advised putting good Burgundy into a coq-au-vin. Anything else would degrade the dish.

Likewise, only use a good T/C, and only put it onto a good lens. Otherwise you just magnify defects.

G

is this a good one http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=170242039686&ssPageName=ADM... and is it worth the money?

Any 2x converter is likely to compromise picture quality. More so than, say a 1.5x one. These days, with DSLR's you're usually going to get better IQ by simply zooming into a non-TC image than actually using a TC in the first place.