[Geoff F]

Firstly, also beware of the Canon converters which will only fit on certain Canon lenses.

With regard to magnification. It all depends on minimum focusing distances. For instance, using Sigma as an example, 50mm has a minimum of 7 ins; 100mm is 12 ins; 150mm is 15 ins.

So a 150mm at its minimum distance would give a bigger image than 50mm at 7 ins. But if we are also considering perfection of photography it could be argued that the bigger lens would give more distortion; although I think you would need close examination of a photo to see much difference.

In reality it probably just comes down to how close can you physically get. If you are only 7 ins away to start with how close can you realistically get without frightening the subject or causing a shadow from the camera under certain lighting conditions.

A 50mm with a 1.4x TC won't give you much advantage over a 100mm regarding magnification and the TC will cause some loss of light and degradation of the image. A new bigger lens will definitely give the best quality, but at a price.

But also consider, if you get a TC, do you have any other lenses which would benefit from its use. But remember that they tend to give poor results with the cheaper zooms.

The decision is yours!