Let's see, you have a D850 with 20-70 and 70-200 lenses and you feel you need another lens to cover the focal lengths you already have covered?! It's a D850 not a D7000. You don't need a 50 or 85 mm fast prime because you have arguably the best 35mm DSLR currently made. If you don't feel the lenses you currently have are fast enough to shoot indoors without a flash then you've been paying attention to the old folks who still live in their glory days of film. Don't be afraid to go past ISO 1600. Your camera will produce clean images even at fairly high ISO'S like 6400 or 12,800 or 25,600. Instead of coveting a lens you can't really afford at this time, why don't you look into buying a good flash unit to go with your excellent camera and more than adequate lenses.

You have grandkids ?? How steady are your hands ?

Your zooms may well have image stabilization. Most
primes do not. I wanted a 50 with in-lens IS [Nikon
calls it VR, generic term is OIS]. I've been very well
pleased with a Tamron 45/1.8 with OIS. So pleased
that I bought a second copy, for my other brand of
bodies. If I needed one for yet a 3rd brand, I'd do it.

For you and your D850, it makes even more sense
than my pair of lower MP SLRs. You can crop much
more than I can, easily imitating a 65 or 70mm/1.8
with no visible loss. The extra 5mm width of view
will be handy for your group shots, and you'd not
really notice it in other applications.

===========================

8 Pros and 2 Cons:

Only $400, excellent imaging, has OIS, feels solid,
operates nearly silently, full time MF-AF override,
has focus scale, tulip hood** included.

BUT ! It's rather bulky for a normal lens. Focusing
scale is good to have, but this one is a bit crowded.

**Since it's kinda bulky, I tested it very thoroughly
for all possibilities of flare. It proved so immune to
flare, even with a filter in place, that I don't use
the hood, thus reducing its bulk. BTW, it's not a
huge lens, just rather bulky for a normal lens.

Let's see, you have a D850 with 20-70 and 70-200 lenses and you feel you need another lens to cover the focal lengths you already have covered?! It's a D850 not a D7000. You don't need a 50 or 85 mm fast prime because you have arguably the best 35mm DSLR currently made. If you don't feel the lenses you currently have are fast enough to shoot indoors without a flash then you've been paying attention to the old folks who still live in their glory days of film. Don't be afraid to go past ISO 1600. Your camera will produce clean images even at fairly high ISO'S like 6400 or 12,800 or 25,600. Instead of coveting a lens you can't really afford at this time, why don't you look into buying a good flash unit to go with your excellent camera and more than adequate lenses.

So I just discovered a box store a half hour from where I recently moved. What a wonderful surprise. I’m still fairly new to all of this. I bought a D850 as my starter camera which caused quite a stir on this forum ;). But I love my new camera and could not be happier with my decision. I will grow with it for a long time. I am ready to add a new lens to take pictures of my brand new and older grandkids. All of them will be here for Christmas. I can’t really get both right now so I’m wondering if a 50mm or an 85mm would be most useful and why? I’d like to take both single portraits and a group setting. Thanks in advance for your responses.