I'm about to move from shooting with an A7RII+A7II to an A7RV+A7RII, and I have tons of (mostly old manual focus) lenses, but I'm thinking it's time to rethink my travel kit. I'll still also grab some of my old manual primes selected based on the kinds of photos I expect to be making, but the real question is how to cover a big range of focal lengths with sufficient IQ so that the A7RV images will actually look better than the A7RII ones...
Last year, I bought two zooms that I think will still be fine at 60MP:
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Tamron 150-500mm f/5-6.7 Di III VC VXD Model A057: excellent long zoom lens, including at the long end, just barely small enough to carry when needed
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Tamron 28-200mm f/2.8-5.6 Di III RXD Model A071: slight upgrade from the surprisingly good A-mount Sigma 28-200mm f/3.5-f/5.6 Macro D Aspherical IF that I used on an LA-EA3
The problem is what to do about wider than 28mm. I have an A-mount Sigma 12-24mm f/4.5-5.6 EX Aspherical DG that isn't terrible until the extreme corners, but it isn't bitingly sharp anywhere and I don't really see much improvement using it on my A7RII vs. A7II; it's really maxed out around 24MP.
My current solution has been three lenses:
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Minolta MC Fish-Eye Rokkor-X 16mm f/2.8: an old lens, but it's still got game
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Venus Laowa 10-18mm f/4.5-5.6 FE Zoom: the widest zoom you can buy, and quite sharp until about 15mm off axis (especially near 10mm), at which point resolution smoothly degrades to the point that the corners are nearly as bad as the old Sigma 12-24mm; it looks crisp on 24MP APS-C, so I think it'll be good on an A7RV's center, but that means the corners will look that much worse...
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Either Sigma 12-24mm f/4.5-5.6 EX Aspherical DG or Vivitar (Kiron) 24mm f/2: to fill the gap between the Laowa 10-18mm and Tamron 28-200mm
I think the obvious no-budget-constraints answer would be to replace the 10-18mm and 24mm solutions with:
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Sony FE 12–24 mm F2.8 GM: probably the best ultrawide zoom made... so far... but, expensive, big, and still not awesome in the corners
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Laowa 9mm f/5.6 FF RL: the widest FF ultrawide, which is a little wider and better than the 10-18mm @ 10mm, but honestly not awesomely better, still dropping IQ past 15mm from the center
The 9mm Laowa is cheap and small enough that, well, maybe? However, the Sony 12-24mm f/2.8 is just too big and expensive to still not really eliminate the soft corners problem. The f/4 version of the Sony is cheaper, but honestly is not a big enough improvement over what I have for the cost. I'd even consider the Canon EF 11-24mm f/4L USM on my Metabones adapter, but DxO gave it a rather disappointing 26PMP rating on a 5DS R, which actually sounds disturbingly close to what I can get with my current lenses. The best option might be the new Laowa 12-24mm f/5.6, which actually looks like it might be sharper than the Sony GM at 12mm (certainly not at 24mm), but is it really enough better to be worth the upgrade?
In sum, I think most ultrawide lenses have growing problems past about 15mm off center. I'm starting to suspect this might be a diffraction limit thing, because these lenses all suffer significant vignetting, and that could make the effective aperture size small enough to have resolution diffraction limited. Especially on the Laowa 10-18mm, the corner softness behaves like diffraction rather than field curvature, etc. If that's the case, it might be a really long time before any compact ultrawide zoom does much better than the Laowa 12-24mm past 15mm off center...
So, what do folks here think? For example, would the Laowa 9mm + 12-24mm be a worthwhile upgrade when used on an A7RV? I think IQ would be visibly a little better, but it also would leave an awkward jump between 9mm and 12mm...