Head-to-Head Comparison

Updated September 5, 2026

Casio MTP-S120L Solar Field vs Seiko Prospex "Turtle"

Casio's field watch meets Seiko's diver

Quick Verdict

The Casio MTP-S120L Solar Field ($100–$150) offers Casio Tough Solar Quartz precision in the tier below the Seiko Prospex "Turtle" ($500–$1,000). The MTP-S120L Solar Field measures 42mm (49 x 42 x 10.9mm) and is rated 100m (10 ATM). The Prospex "Turtle" counters with Made in Japan craftsmanship and 200m (20 ATM) Diver water resistance. Both are exceptional watches for their respective tiers.

CasioMTP-S120L Solar Field$100–$150 Check price SeikoProspex "Turtle"$500–$1,000 Check price

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Casio

MTP-S120L Solar Field

$100–$150

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Seiko

Prospex "Turtle"

$500–$1,000

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Specifications Compared

Feature	Casio MTP-S120L Solar Field	Seiko Prospex "Turtle"
Price	$100–$150	$500–$1,000
Case Size	42mm (49 x 42 x 10.9mm)	45mm
Movement	Solar-Powered Quartz	Automatic Caliber 4R36
Caliber Type	Casio Tough Solar Quartz	In-House Automatic Manufacture
Power Reserve	Months on a full solar charge; no battery replacement	41 Hours
Water Resistance	100m (10 ATM)	200m (20 ATM) Diver
Crystal	Mineral Crystal	Sapphire Crystal
Case Material	Stainless Steel	Stainless Steel
Origin	Casio (Japan)	Made in Japan

Category-by-Category Analysis

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Design & Aesthetics

Edge: Draw

Casio's design language vs Seiko's approach

The Casio MTP-S120L Solar Field features a Stainless Steel case at 42mm (49 x 42 x 10.9mm) with Mineral Crystal protection. The Seiko Prospex "Turtle" offers Stainless Steel construction at 45mm with Sapphire Crystal. Both represent their brand's distinct design philosophy and heritage.

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Movement & Performance

Edge: Seiko

Solar-Powered Quartz vs Automatic Caliber 4R36

The MTP-S120L Solar Field runs the Solar-Powered Quartz (Casio Tough Solar Quartz, Months on a full solar charge; no battery replacement power reserve) at standard frequency. The Prospex "Turtle" uses the Automatic Caliber 4R36 (In-House Automatic Manufacture, 41 Hours reserve) at 21,600 vph (3 Hz). The Prospex "Turtle" offers a longer power reserve.

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Wearability & Fit

Edge: Casio

42mm (49 x 42 x 10.9mm) vs 45mm — different wrist presence

At 42mm (49 x 42 x 10.9mm), the MTP-S120L Solar Field wears more compactly on smaller wrists compared to the Prospex "Turtle" at 45mm. Water resistance differs: 100m (10 ATM) vs 200m (20 ATM) Diver.

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Value & Cost of Ownership

Edge: Casio

Casio sits in the lower tier

The Casio MTP-S120L Solar Field sits at $100–$150 and the Seiko Prospex "Turtle" at $500–$1,000. On the specs that outlast any price: the MTP-S120L Solar Field uses Mineral Crystal with Months on a full solar charge; no battery replacement, against Sapphire Crystal and 41 Hours on the Prospex "Turtle". Service intervals are typically 5-7 years for both.

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Water Resistance

Edge: Seiko

100m (10 ATM) vs 200m (20 ATM) Diver

The MTP-S120L Solar Field is rated to 100m (10 ATM) while the Prospex "Turtle" handles 200m (20 ATM) Diver. The Prospex "Turtle" offers superior water resistance.

Our Verdict

Casio

MTP-S120L Solar Field

Choose the Casio MTP-S120L Solar Field if you prioritize Casio Tough Solar Quartz engineering, Casio (Japan) craftsmanship, and 100m (10 ATM) water resistance. At $100–$150, it delivers Solar-Powered Quartz with Months on a full solar charge; no battery replacement power reserve.

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Seiko

Prospex "Turtle"

Choose the Seiko Prospex "Turtle" if you value In-House Automatic Manufacture technology, Made in Japan heritage, and 45mm proportions. At $500–$1,000, the Automatic Caliber 4R36 with 41 Hours power reserve makes it a compelling choice.

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The Bottom Line

The Casio MTP-S120L Solar Field and Seiko Prospex "Turtle" represent two distinct approaches to fine watchmaking — the Casio bringing Casio (Japan) tradition while Seiko delivers Made in Japan engineering.

Frequently Asked Questions

The Seiko Prospex "Turtle" is the better buy if you want a mechanical movement; the Casio MTP-S120L Solar Field is the better buy if you want solar power and quartz accuracy with no servicing. For water, the Seiko Prospex "Turtle" is rated 200 m against 100 m, which is the difference between swimming and diving on one side and splashes on the other. On price, the Casio MTP-S120L Solar Field sits a band lower ($100–$150 against $500–$1,000), so it is the cheaper way into the category. Neither is better at everything; the spec table above shows movement, case size, water resistance and crystal side by side so you can weigh what matters to you. We do not test units, so this is the makers' data, not a bench result.

The Casio MTP-S120L Solar Field offers better upfront value, sitting a tier lower at $100–$150. However, the Seiko Prospex "Turtle" may justify its premium with superior finishing, heritage, or resale value.

Both are suitable for daily wear. The MTP-S120L Solar Field at 42mm (49 x 42 x 10.9mm) with 100m (10 ATM) water resistance handles everyday situations. The Prospex "Turtle" at 45mm with 200m (20 ATM) Diver is similarly capable. The MTP-S120L Solar Field uses Mineral Crystal while the Prospex "Turtle" uses Sapphire Crystal. Sapphire resists scratches noticeably better than mineral glass.

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How This Page Was Made

Our comparisons are generated from a hand-maintained specification database and reviewed under our editorial standards. We use AI tools to assemble pages from that data. We don’t invent specs: every number traces back to the database, and when we correct an entry, the fix is applied site-wide. As an Amazon Associate, The Horologist earns from qualifying purchases.