My universe broke when Sigma introduced an 18-35mm f/1.8 zoom. An f/1.8 zoom. Wow. And it was optically brilliant.
Seventies lenses are super-sharp, but that's because they're mostly slow primes. Any modern prime stepped down to f/5.6 -- even cheap consumerific ones -- will be super-sharp.
There's nothing in seventies technology which allows lenses to have the aperture, zoom range, and aberrations of modern ones.
What those old lenses have so, is build quality. They are machnical master pieces, as oppossed to modern day plastics. I like that. Also, close to no electronics that can fail.
Those wide zoom ranges, and large appertures, do have other downsides so. Everything is a trade off, and some things are sacrificed to achieve a 18-35/1.8 lense. Still impressive. Or the latest Canon (?) patent on a tilt-shift-macro-zoom...
It's possible due to things like:
- Much better lens coatings (allowing for more elements without flare)
- Computer modelling
- Being able to better machine aspherical elements
On integrated cameras, like an RX100, we can do even better due to digital. We don't need low-distortion, but just well-characterized distortion which a computer can invert.
Those old lenses -- at least the ones still working -- do have build quality. Adjust their prices at the time for inflation, and have a look at modern Zeiss, Leica, and other premium lenses. You'll see similar build quality.
For fun, next time you're looking at old lenses, pick up a Quantaray too, for fun. Or most older (before around 2000) Sigma lenses. Or other off-brands. You'll see unparalleled build quality, but in the other direction -- eighties-era plastic. The optical quality is bad. Not "fun" bad, "vintage" bad, or "whimsical" bad, but just bad.
When we look at older stuff, we tend to look at stuff which stuck around, but even that Quantaray is high-end compared to an older consumer camera. Most people who owned a camera had a non-SLR one. You looked through a little window on top, and the pictures were shot through the main lens. Those were even worse. Or a disposable (a single plastic element lens).
f/2.7, sharp at fully open, parfocal, zero focus breathing, fully manual zoom lenses...
and what used to be...
f/5.6, sharp only when stopped down even further, massive focus breathing, prime lenses...
well, vintage lenses start to look like toys.
Of course, if it's a F/1.8
Roughly the same optical design, limited to f/2.8, will be better in all respects.
A good way to think about this -- oversimplified obviously -- is you have a bunch of functions you're trying to cancel with e.g. a linear combination. If you look really close to the center, it's already a flat line. If you step out a little, two are adequate (have the slopes cancel). As you go further and further out, things become increasingly wonky. That's why you have super-complex designs for an f/1.8 zoom -- to get that cancellation right -- but even a single element works fine at f/22.
There actually were f/1.8 zooms all along, but for applications which didn't demand that sharpness (TV and CCTV). You can pick those up cheap and see what happens. They're sometimes fun on a real camera too (many will span a μ4/3 sensor with just a tad of vignetting).
