It's not as if sony lenses are any cheaper or better than Nikon equivalents...
Well... in most cases the Sony equivalents are lighter and optically superior. Nikon has fantastic glass, but every Sony design is brand new and most are optimized for modern high resolution cameras. Look at the DXO scores yourself. Plus, In many cases, they are cheaper than Nikon. Want a small, low weight, high IQ ultrawide lens, compare the Sony choices with the Nikon choices.
The Sony zooms look to be a decent range, although similar in size and cost to the Nikons.
The primes are an odd mishmash of big and expensive, and not particularly compact or fast or inexpensive. There's nothing like the range of prime choices, below 100mm, let alone above.
It’s a bit more complicated than that.
The primes are very comparable, or slightly smaller, than lenses of similar overall quality.
But it's even more complicated than that! In the sense that a lens is a package of attributes - size, speed, cost and optical performance.
For me, with any reasonable brand post 1990 prime lens, the optical performance is secondary. I'm interested in people, events and travel; not landscapes-on-a-tripod so I can admire edge sharpness on a huge print.
The "technical" quality-limiting attributes for my photos are shutter speed and iso, and DoF control. I've rarely ever looked at a photo where the optical performance was an issue (except perhaps bad flare occasionally). If the composition and focus was right, the issue will be noise or lack of DR at high ISO, or some subject motion due to low shutter speed. Therefore compact fast primes are more important to me than optically perfect primes
So look at the 50/1.4 for example. Optically top notch.. better than the Nikon 50/1.4. And heavier than the 50/1.4. But the best 50/1.4 for Nikon is actually the Sigma ART—- which is bigger and heavier than the Sony.
Exactly. The point is there's no one person's set of priorities which are a universal truth. I want a good 50 1.4 for the speed and compactness. The Sony one and the Sigma ART are ludicrously big for a 50, like the Leica SL 50 1.4.
The Nikon 50 1.4 is both cheap and compact in comparison and there's nothing more I need from it optically. So whilst for you the Sony 50 1.4 is a win for the Sony system, for me it's the opposite.
Meanwhile, for 1.8 primes... the Sony 50/1.8 is similar in size, price and quality to the Nikon 50/1.8— The Sony 55/1.8 is much more expensive but optically far superior while still being small.
My 50 1.8 is an AF-D. About $100 and looks to be half the lengthy of the rather long Sony 50 1.8. The 55 1.8 is nearly 3x the cost of a Nikon 50 1.4. Pointless.
At 85/1.8... the Sony is actually a little cheaper than the Nikon, similar size, and optically superior (I’ve used both lenses. The Nikon is great but the Sony is brilliant).
Fair enough. 85mm is probably the one focal length where the two systems are most comparable and if you say the Sony 1.8 is better I'll take your word for it. Ditto for the 1.4. (But, personally, I suspect the optical betterness of the Sony is immaterial to my needs.)
I have a Nikon 85 1.4 AFS, but also an 85 1.8 AF-D. That is really small and works for everything except low light when I want the last 1/2 stop from the 1.4
And there are plenty of choices, fast and less fast, from about 25mm to 100mm.
Not really "plenty" in comparison to the Nikkor line. You've picked some highlights but let's look at 35mm. There's a big 1.4, fair enough. And a very slow 2.8 - nothing in between. Nikon has a big 1.4, a very good 1.8 and a nearly pancake 2.0 AFD.
Under 25 and over 100, Sony is a bit lacking in primes.
Exactly, but that leaves 85mm as the most competitive prime length for Sony, and 50mm if optical perfection is your goal rather than (for me at least) the more traditional thing for a 50 which is versatility - low cost/fast/small. Otherwise there are a few other good primes of course, but it's nothing like as complete a system relative to the
choices in the F mount.
It's why for me, at least, the "size benefit" of the Sony system is illusory. If I want to carry my big 1.4 primes and 2.8 zooms, the extra few hundred grams of a Nikon DSLR are immaterial. If I want to go compact but still benefit from FF sensor performance and DoF control, I can assemble a more compact fast system with Nikon primes IMHO.
To make it clear these are honest preferences rather than fandom, I will say that I suspect for my needs, the latest Sony AF system is better than Nikon's. I don't care about sports AF tracking, which most reviews go on about. Reading Jim Klasson's blog article about using the D850 and A7Riii for family events, I think the accuracy of the Sony AF system plus the eye detection is something I'd prefer to even D5/D850 AF.