You would know this George. My longest lens is the 150-600mm Sigma. Works very well with my Full Spectrum Nikon D810. Still would like a little bit more focal length. Would you recommend a Sigma 1.4 teleconverter to boost my focal length to 840mm?
In my opinion, I would do it provided that the teleconvertor and lens are all compatible. You will lose a bit of light and have to bump your ISO, but I would go for it. Your PA will need to be really good because of the focal length you are shooting at. I would NOT do a 1.7 or 2x tele.
I am getting the 1.4 Sigma Teleconverter for my 150-600mm Sigma lens. It is for Nikon cameras as well. Shouldn't be a compatibility problem. I will let you know how it works out. I found a 1.7 Nikon teleconverter but wouldn't attach to the Sigma 150-600 lens. It was for a crop sensor NIkon I have from days gone by.
