Sigma has some fantastic E-mount options for the a7 IV.

The Sigma 24-70mm f/2.8 DG DN II Art is an excellent pro-level alternative to the Tamron 28-75mm, offering superior image quality and sharper results, though it's heavier. Perfect for everyday shooting with smoother bokeh and excellent video performance with smooth focus transitions.

For portraits, the Sigma 85mm F1.4 DG DN is incredibly lightweight at just 630g and sharper than even Sony's GM version in most cases. It's also about $700 cheaper than Sony's equivalent!

The Sigma 100-400mm F5-6.3 DG DN OS is a great budget telephoto option, though AF isn't quite as fast as native Sony lenses.

For macro work, the Sigma 105mm f/2.8 DG DN Macro Art is outstanding with genuine 1:1 reproduction and exceptional sharpness.

All these lenses offer excellent value while maintaining professional image quality. What type of photography are you planning to focus on?

For portraits, consider Sigma's 85mm f/1.4 DG DN. Optically superb, but very sharp wide open – be mindful of that for skin detail. Have you considered a diffusion filter? I'd strongly advise checking lens distortion profiles in post-processing software; correct them diligently. Also, always shoot RAW for maximum adjustability. Maybe consult a pro photographer about your specific needs?

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For portraits, consider Sigma's 85mm f/1.4 DG DN. Sharpness is great, but more importantly, its solid build gives me confidence when shooting in unpredictable weather; a dropped lens is a safety hazard!