Alpinist SPB507 the green field watch gets slimmer and goes 72 hours

What is new about the Alpinist SPB507?

The SPB507J1 is the green, leather-strap member of the eighth-generation Prospex Alpinist, announced in autumn 2025 alongside the bracelet-fitted SPB503 (teal) and SPB505 (black). It replaces the SPB121, which arrived in 2020 and became the default green Alpinist.

The headline change is inside. The old calibre 6R35 gives way to the 6R55, which Seiko rates at about 72 hours of power reserve, up from 70. The case is also half a millimetre slimmer at 12.7 mm, and Seiko now applies its super-hard coating to the steel for better scratch resistance.

The dial is the other story. Watches by SJX points out that the colour-matched date wheel with a gold outline returns, along with an italic gold Alpinist script under the Seiko logo. The compass ring printing has switched from white to gold. Together these make the SPB507 closer to the 1995 green Alpinist than either of the two generations in between.

How big is it, and how will it wear?

Seiko lists the case at 39.5 mm across, 12.7 mm thick and 46.4 mm from lug to lug, with 20 mm lugs. Those are the same width and length as the SPB121, so anyone who liked the old fit will find nothing to relearn. A 46.4 mm lug span sits comfortably on most wrists, including smaller ones that struggle with 42 mm sports watches.

On its leather strap the watch weighs 88 g, according to Seiko, which is light for a 200 m steel tool watch. The second crown at 4 o'clock turns the internal compass bezel, and the crown guards around the main crown give the case its slightly chunky, outdoorsy profile. The magnifier over the date window stays, so this is not a watch for anyone who dislikes a cyclops.

What movement does it use, and how accurate is it?

The 6R55 is an in-house automatic running at 21,600 vibrations per hour with 24 jewels. It hacks, hand-winds and has a quick-set date, which puts it a clear step above Seiko's entry-level 4R calibres. You can see it through the exhibition caseback, though the finishing is plain machine striping.

Seiko quotes accuracy of +25 to -15 seconds per day. That is the same tolerance as the outgoing 6R35, and it is wide for an £850 watch. Swiss rivals at this price often quote tighter figures. Most Seiko movements run well inside their stated range, but the official spec is all Seiko guarantees.

How well is it built?

The specification is strong for the money. There is a sapphire crystal with an anti-reflective coating on the inner surface, a screw-down crown, 200 m water resistance and magnetic resistance of 4,800 A/m. LumiBrite covers the hands and indices. The leather strap closes with a three-fold clasp and push-button release rather than a simple buckle, which is a nice touch at this level.

The super-hard coating should help a watch that, by design, is meant to get knocked about. Time and Watches notes that the case keeps the screw-down caseback heritage that defined the first 1959 Alpinist, now with a mountain motif on the back.

Is it good value against its rivals?

The RRP is £850. The bracelet versions, SPB503 and SPB505, cost £940 on Seiko UK. The closest Swiss alternative is the Hamilton Khaki Field Auto 38 (H70455533) at a £640 RRP on Hamilton UK. It is smaller at 38 mm and 11 mm thick, offers a longer 80-hour reserve from its H-10 calibre, but only 100 m of water resistance and a plain pin buckle.

So the Hamilton is cheaper and slimmer, while the Alpinist gives you twice the water resistance, a compass bezel, a folding clasp and a more distinctive dial. If you want a field watch that can handle a lake swim and a dinner, the Seiko makes the stronger case. If you want the cleanest, most classic military field look for less, the Hamilton does.

What is the catch?

Price is the first one. Mr Stateless notes that the new generation costs more than the one it replaces, and the upgrades are evolution rather than revolution. Owners of the SPB121 have little reason to switch.

Accuracy is the second, as above. The third is the strap. Owners of the previous model often say the factory leather is the weak point and swap it quickly, and the Alpinist's 20 mm lugs make that easy. Budget for a second strap if you plan to wear it daily.

“The new Alpinist looks more like the 1995 original than any green Alpinist since.”

What do owners say?

Themes from public owner feedback, paraphrased. We never copy Amazon reviews or ratings.

• Owners of the previous model praise the 39.5 mm case as comfortable and versatile enough to wear with a suit or casual clothes

  Dialicious owner review (opens in a new tab)

• Owners of the previous model say the original leather strap feels low quality and replace it

  Dialicious owner review (opens in a new tab)

• Accuracy tolerance is a common criticism for the price, though many owners report results well within spec

  OzBargain comments (opens in a new tab)

• Seen as a strap monster that takes NATOs and aftermarket bracelets well on its 20 mm lugs

  OzBargain comments (opens in a new tab)