Jamie Dornan was totally open to showing his penis in the movie. (But, alas, he doesn’t.) “Showing penis was definitely an option; nobody ever said ‘do it’ or 'don’t do it.’ We set up shots not thinking about that and there were a couple of times when it came really close. But that wasn’t on purpose. It was just where the camera was.
—  James Foley, Marie Claire
It was a very harmonious adventure mainly because Jamie and Dakota had developed a relationship since the last movie and even they told me when they really bonded on the publicity tour that went on for a long for a long time and the kind of craziness started. So by the time we started they were very tight and made each other laugh. Jamie was incredibly protective of her, of Dakota.
—  James Foley (Fifty Shades Darker Premiere)
The easiest scene to film was, surpisingly, when Christian flipped Ana over with the spreader bar. I don´t know why it was the easiest, but it was. The day before, we had our BDSM expert there showing us how to do this and do that, and I thought, Man this is gonna be hard tomorrow. And I don´t know what happened. I came to the set, Dakota´s in this great mood, like bouncing on the bed saying, “Let´s do this!” And we did it very quickly and (Dakota and Christian) were having a very good time. I mean, she was just giggling all over the place. So that one was easy.
—  James Foley
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#FiftyShadesDarker Premiere in LA 2/02/17 #ELJames #JamesFoleyJr #JamieDornan #DakotaJohnson 🎬🙌💋📽

(via https://www.youtube.com/watch?v=8ySVZrmawM0)

The elevator scene was the hardest scene for Dakota to shoot. “It was a fake elevator. It was just a wall back there and we were all out here, so it wasn’t too bad in terms of being cramped. But it was in terms of Dakota getting into it. [She] said that it was the hardest scene for her to shoot. I was so surprised because it wasn’t that explicit or anything, but she said she’s surrounded by these extras, these strangers.
—  James Foley, Marie Claire 
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Fifty Shades Darker Premiere in Madrid on February 8th, 2017