Sigma's constant-f/4 ultra-tele zoom — a 2025 300-600mm for Sony E and L-Mount.
The Sigma 300-600mm f/4 DG OS Sports is a constant-aperture f/4 ultra-telephoto zoom for full-frame Sony E and L-Mount mirrorless cameras, announced on 24 February 2025 with availability from April 2025. It is the flagship of Sigma's Sports line and one of the boldest lenses of its generation: a zoom that holds f/4 all the way to 600mm, territory previously reserved for six-figure-yen exotic primes and Sony's own £13,000-class 600mm f/4 GM.
The optical design comprises 28 elements in 21 groups with six FLD and one SLD element and a water- and oil-repellent front coating. Autofocus is driven by Sigma's HLA (High-response Linear Actuator), and the OS2 stabiliser is rated to around 5.5 stops at 600mm. It uses a 40.5mm drop-in rear filter holder rather than a front thread, features an internal zoom with constant length and balance, a magnesium and carbon-fibre-reinforced construction, function buttons, focus limiter and a robust integrated tripod collar. It measures 167mm by 467.9mm and weighs 3,985g, and on L-Mount it is compatible with Sigma's teleconverters for up to 1200mm equivalent reach.
Its significance for UK buyers is value at the extreme end: at $5,999 US (around £5,499 UK) new, it delivers 600mm f/4 light-gathering for roughly 40 per cent of the price of first-party 600mm f/4 primes, with the added flexibility of zooming out to 300mm f/4. Reviewers, including Dustin Abbott, judged its sharpness genuinely competitive with primes. Used examples are scarce and hold value strongly, appealing to bird and sports photographers who could never justify a GM or Lumix-exotic prime; on Sony bodies note the usual third-party burst-rate cap of 15fps.
For a used purchase, this lens deserves an in-person inspection given the sums involved: check the front element and rear drop-in filter slot (confirm the standard 40.5mm holder is present), test OS in both modes for smooth viewfinder behaviour, and run AF at 600mm on a distant subject to confirm the HLA drives without hesitation. Examine the tripod foot, collar rotation and strap lugs for stress wear, as most copies live on monopods. Look for transport damage such as dents in the huge hood and check the barrel for fungus if stored in a case long-term. Ask for the original Sigma hard case and proof of purchase for warranty transfer, and verify firmware is current. Expect used prices only modestly below the circa £5,499 new price while supply remains thin; anything dramatically cheaper warrants extra scepticism.