Sigma 17-50mm f.8

Advantages

• ✓Sigma is smaller and lighter, making it more travel‑friendly.
• ✓Sigma offers a stronger 4‑stop optical stabilization versus Canon's 3‑stop IS.
• ✓Closer minimum focusing distance (0.28 m vs 0.35 m) gives better macro capability.

Disadvantages

• ✗Canon provides a full‑time manual focus override and a more robust metal construction.
• ✗Canon may exhibit slightly better corner performance at the wide end.

Advantages

• ✓Sigma delivers faster HSM autofocus compared with Tamron's slower micro‑motor.
• ✓FLD and aspherical elements in Sigma provide superior aberration control and contrast.
• ✓Sigma's build, while plasticky, includes a protective case and hood as standard.

Disadvantages

• ✗Tamron is similarly sized and slightly lighter, and may be priced lower (price not listed).
• ✗Both offer 4‑stop stabilization, so no clear advantage there.