[Rob Barron]

I think the important thing to remember when buying a TC is that you should approach it like any other lens. Most TCs have at least 3 or 4 and sometimes up to 7 or 8 elements internally so there will always be an effect. How much of an effect depends largely on the quality of the TC purchased.

I used to have a Jessops own brand 2x TC and frankly it was distinctly average. Even on a lens I knew was normally very sharp, images usually suffered from soft focusing, especially at the wide ends of the aperture. However, i got the Canon 2x TC and that problem has all but disappeared. On the one hand the elements used in these are of the same standard used in their L series lenses but on the other hand they cost three times the price! I believe Steve uses a pro range by Kenco which he is also delighted with.

The only true comparison is to take a picture with a 200mm + 2x TC and compare it to a picture taken with a 400mm lens. With the top quality TCs I think you will find the difference to be very acceptable though yes, there might be some lack of sharpness at the widest apertures. You know about the loss of light factors so I shalln't go into those.

The better ones will keep AF on L series lenses at up to f5.6 which is very handy though of course distance work is not exactly hard to manually focus anyway!

Ultimate question: would I buy one? obvious answer, given that I have already said i own one, is yes. I wouldn't use it unless I needed extreme range but i have used it with my 300mm L prime lens to give me 600mm f8 and it is excellent. I don't have a 600mm lens to compare it with and i am unlikely ever to have one! I would definitely go for a quality one though, not sure how much Nikon ones are but the kenco pro one is excellent so is a viable alternative. Steer clear of adding a cheap make onto a quality lens: it WILL make a difference.

Cheers,
Rob