UKC

I was wondering if it would be worth using a TC on my sigma 105mm f2.8 lens - its a macro lens but should work just as well for wildlife to give a flat field of view I think.
Question is, is it worth getting a TC? Ive found a two times converter that would let me use my lens in manual focus, for about £80, so would effectively give me a 210mm f4.8 on my crop sensor camera. I would ideally like a 400mm lens for wildlife etc but theres no way I can afford one of those.
Ive already got an 18-200mm lens but as youd expect its not very sharp at 200mm.
What do you think?

In reply to ow arm:

Remember you will lose 2 stops with a 2x teleconverter, so your 105mm f/2.8 becomes 210mm f/5.6

I'd expect a cheap 70-300 f4/5.6 zoom to give comparable or better performance at 210mm than a 105mm plus cheap 2x teleconverter. Plus it will give you AF, more versatility and a faster max aperture for most of the zoom range.
You may find you need AF a lot more for wildlife than for macro shots.

In reply to ow arm:

If you don't mind manual focus then it might be easier to just get an old prime lens, as they will probably be faster and sharper. I got a 200mm F/4 and 300mm F4.5 for my Nikon for around £100 each. London Camera exchange or ebay will probably have some examples you could consider.
Manual focus at 300mm can be tricky unless you have stationary subjects and liveview!

In reply to richard_hopkins:

those are all fair points, ive come to the same conclusion with the aid of nikonites forum too.
ta