I have used one in the past and results are mixed. On my old 200mm-500mm zoom lens it was next to useless as autofocus would not work due to light loss, and image quality was worse than using the lens on its own and cropping the final image more. With my 500mm prime lens, it's ok although on distant birds where you haven't got much detail anyway, you tend to lose what bit you have got.
Yes, so a 300 mm lens becomes 420 mm, a 500 mm becomes 700 mm and so on.
Bear in mind though that you will generally lose one stop on the exposure and that it may not work with zoom lenses. AF speed and effectiveness can also be worsened.
Also, think about the quality of glass you are using - I wouldn't expect to stick a £40 'no name' extender on the back of a £1,500 branded prime lens and not see the image quality fall off dramatically.
That said, I use a Nikon 1.4 extender on a 300 mm F4 lens and have no problems with that combination.
Hi, I've seen an ad on EBay for a 1.4 extender, for a Canon camera. Am I correct in assuming that this will multiply my current lense by 1.4? Thanks, Joe
