[scoff]

Are these worth getting to extend the range of my existing kit, or a waste of money?
TIA

[CT]

It depends how good your lenses are. A TC will give better results with a prime (fixed focal length) lens than it will with a zoom lens. Having said that better quality zooms do return good results with a TC.

If you stick a TC behind a lens which is a mediocre performer to begin with then you'll be disappointed, as the TC will just magnify any shortcomings which were there to start with.

I certainly don't think they're a waste of time. They make lot of sense financially compared to buying a lens, especially if it's something you wont be using all the time. Just make sure you get a good one and avoid any cheapies.

[evilowl]

If this is your kit (sorry I copied and pasted from another thread)

Originally Posted by scoff

Cannon EOS 300D | 18-55 Cannon lense | sigma 70-300 APO DG Macro |Sigma EF-500 DG ST Flash

then I'm pretty sure you won't be able to use a teleconvertor with either of your lenses. Sigma have a compatability chart for their lenses here:

Sigma Imaging (UK) Ltd

You need a deeply recessed lens on a zoom (where the lens meets the camera body) so that the rear glass element does not come into contact with the front element of the teleconvertor when you are zooming in and out.

[Joe T]

Further to what evilowl said, I think you also need a USM/HSM/etc lens - i.e. with a focusing motor built into the lens.