Calson
Well-known member
A 800mm PF with f6.3 would be interesting depending on the price. As it provides twice the image size of the 500mm PF lens it would be great for small animals but I would also expect it to need to be used on a tripod or monopod as any camera movement is going to be magnified more as well.
What is an inherent problem with a DSLR is having a different light path for autofocus than for exposure so it can never be completely accurate. AF fine tuning helps but a 200-500mm lens for example that has an AF Fine Tune adjustment setting for it at 500mm is going to be less accurate at a 200mm zoom focal length. Even a prime lens that is adjusted with a target distance of 40 meters is going to have its accuracy diminished at shorter or greater distances. It is why I still use manual focusing most of the time and why Nikon provides lenses with AF manual override.
What is an inherent problem with a DSLR is having a different light path for autofocus than for exposure so it can never be completely accurate. AF fine tuning helps but a 200-500mm lens for example that has an AF Fine Tune adjustment setting for it at 500mm is going to be less accurate at a 200mm zoom focal length. Even a prime lens that is adjusted with a target distance of 40 meters is going to have its accuracy diminished at shorter or greater distances. It is why I still use manual focusing most of the time and why Nikon provides lenses with AF manual override.