2 x converter

Hi all
I'm in two minds as to whether to buy a 2x converter for my SF7. I want to use it in conjunction with an 80-200mm zoom lens.
Q. do these things really work and if so what are the drawbacks (if any). Please help as I've only been into SLR for about 2 months and still don't know what I'm talking about.
Cheers

ivorpits

I use one on all three of my slr's. They do work, in doubling the focal length, but they also reduce the amount of light reaching the film. Not really a problem in good light, but in poor or fast changing light it can be a pain. I've just bought a 300mm fixed telephoto lense to get around this problem.
It does make my 50mm f1.7 into a nice portrait lense though.

A 2x Macro Converter will in particular convert a 50mm lens into a pretty good 100mm macro.

In general, though, copnverters do magnify a lens's abberations and results can be downright poor if the match is not good.

I would suggest using the appropriate pentax converters and using them with the designated lenses, usually telephotos. Of cousrse, this does not mean we can't experiment with "inapproprate" combinations - some results could well be interesting....