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Nikon D90 – Lens Help?
Hello, I have a Nikon D90 and make a lot of sports photography, I'm looking at getting a 70 or 80-200 f2.8. Without But he can not afford the Nikon AF-S, only the AF, but I have understood that the AF is not compatible with Nikon teleconverters. I've also been looking and Sigma Tamron lens equivalent. Any advice on what you should get (brand of lens and teleconverter) would be great and also the pros and cons of the Sigma Tamron and the D90. Thank you.
You want to use a teleconverter with the lens. Nikon teleconverters only work with AF-S, so no luck with them. However, there was telecoverters brand.
Nikon D90 Sample Video