best 50mm interview lens for FS7 mark II? Is this a contender?

https://www.bhphotovideo.com/c/product/1299222-REG/sigma_50mm_f_1_4_dg_hsm.html/BI/2855/KBID/3801 (https://www.bhphotovideo.com/c/product/1299222-REG/sigma_50mm_f_1_4_dg_hsm.html/BI/2855/KBID/3801/BI/2855/KBID/3801)

There is no one 50mm that is the "best". It all depends upon what you want in a lens and your budget.

The Sigma you linked is an excellent lens in the budget realm for interviews. The Canon 50mm f/1.2 EF is in roughly the same price range and it is a lens many Fs7 / C300 owners love and use for interviews where they are wanting to achieve a shallow depth of field. For a bit more money there is the Sony Planar T* FE 50mm f/1.4 ZA Lens which has the advantage of having an iris ring and also comes in e-mount, so you won't need a lens adapter. By avoiding a lens adapter you avoid any issues with the adapter producing flare. Another option for a 50mm that provides manual iris control is the Rokinon 50mm T1.5 Cine DS. At only $400 it is a bargain. For around half the price of some of the 50mm's mentioned you could get the Rokinon 50mm T1.5 and the Rokinon 85mm T1.5.

excellent reply - looking at that Sony Planar T* FE 50mm f/1.4 ZA

thanks

If your budget allows, I would check out the Tokina 50 Vista. Its more expensive than some of the other suggestions but it punches way above its price tag. Its beyond full frame coverage, interchangeable mount and a very nice modern and sharp look. No breathing and beautifully marked for pulling focus. Its probably the last 50mm you would ever buy.