If it is a Sigma lens made for Nikon it will work but I would recommend you to reconsider this step. As far as I know the Sigma has an aperture of 5-6.3 remember if you put a 2x converter in between it will double that too so 10-12.6 aperture and with those aperture values I have to be honest, you have to have perfect weather to get just a certain slightly good image. and then the question of what do you want to shoot with a 300-1200 lens?

Greetings KingRaven90

Unfortunately, I can't answer that. But why buy a Nikon converter for a Sigma lens? Sigma offers a 2x converter that is compatible with 150-600 (http://www.sigmaphoto.com/lenses...).

Hello everyone, thank you for the answers.
I also own the 24-70 and 70-200 /2.8 from nikon and it would of course be cool if I could use all my lenses with the same converter. I use the sigma almost exclusively with a tripod. I have already seen that sigma also offers a 2.0.

Greetings martin

Hello, please keep in mind that using the 2x converter also doubles the aperture. Technically, you need to have a very, very steady hand or definitely work with a tripod and remote release.
I personally work with Nikon D90 and the 70-200 / 2.8 lens. The converter works very well there. The autofocus takes a little time at the beginning... but then works very well. The last time I used it in a storm, it was not possible to use it properly without a support on my backpack-that's why I used a tripod!
Greetings M.L.