Pentax Papilio II 8.5x21 Review

Overview

The Pentax Papilio II 8.5x21 isn’t trying to be your everyday birding binocular — it’s built around one party trick: focusing down to 1.65 feet, which is roughly 10x closer than a typical compact binocular can manage. That makes it a niche pick, but for anyone who wants to look closely at butterflies, insects, flowers, or trailside detail (and still glass a distant ridge when needed), it’s one of the few tools that does both jobs in a 289g package.

Key Specs

Spec	Value
Magnification	8.5x
Objective lens	21mm
Prism type	BAK4 reverse Porro
Exit pupil	2.5mm
Eye relief	15mm
Apparent FOV	51°
Field of view	315 ft @ 1000 yds (6°)
Close focus	1.65 ft (0.5m)
Tripod socket	1/4”-20
Dimensions	4.57 x 4.33 x 2.1 in
Weight	289g (10.2 oz)

Performance

The close-focus ability is the whole reason this binocular exists, and by every account it delivers. Pentax uses what it calls a convergent lens system that moves the objectives closer together as you focus in, which is a feature not used on any other binocular, where the objective elements move closer together at close focus, effectively minimizing the need to cross your eyes when using the bino in extreme close ups. In practice, that means you can watch a moth’s proboscis or an ant tending aphids without your brain fighting to merge two overlapping images — the design is doing that work for you.

Birders-turned-naturalists seem to be the biggest fans. One longtime user on the John Muir Laws site put it simply: they work great on distant birds with a bright, clear image but also can focus on insects or flowers that are only 18 inches away, so you can actually watch ants tending aphids or see the tongues of bees as they feed at flowers. That dual-purpose capability is echoed across forums — the Papilio II focuses to a distance of 0.5 meters which is magnitudes closer than any other binocular at any price.

Where the compromises show up is exactly where you’d expect from a 21mm objective and 2.5mm exit pupil: low light. One BirdForum user who compared the 8.5x to a full-size compact noted the fov is too restrictive and the exit pupil is too small for use in less than good light plus also a bit finicky to get eye placement right. That tracks with the physics — a 2.5mm exit pupil is fine at midday but starts to feel dim at dawn, dusk, or in shaded forest, which matters if you’re also hoping to use these for general birding.

Optically, for the price, reviewers are consistently impressed. One detailed field review rated body construction and optics decently and noted image brightness as good to very good, when compared to other compact bins in this price range, while acknowledging higher spec compacts, with larger objectives and the highest quality optics do perform slightly better, but then they also cost a whole lot more. Field of view is respectable for a compact — with an angle of view of 6.0° the width of the view through the 8.5x21 Pentax Papilio is 315ft wide at 1000 yards, which is wide enough to track a moving butterfly without constantly losing it.

The focuser gets consistent praise for smoothness. Multiple reviewers independently describe it as fluid and precise — one noted the focusing system uses a small knurled knob that offers excellent fluidity of movement, though the 8.5x format offers a shallower depth of field than the 6.5x version, meaning you’ll need to focus more carefully at extreme close range. That shallow depth of field at 1.65 feet is worth flagging: a couple of forum users mention that at true minimum focus, any slight hand movement throws you out of focus, which is why several serious users mount the Papilio on a tripod via its 1/4”-20 socket for extended macro sessions.

Build quality is basic but functional — this is a budget-tier compact, not a premium alpine binocular, and it’s priced accordingly. Eye relief at 15mm is on the shorter side, so eyeglass wearers may lose some field of view at the edges, and the diopter ring isn’t lockable, though it does have click-stops to resist drifting.

Pros & Cons

Pros

• Unmatched close focus (1.65 ft) — nothing else in this price range or arguably at any price comes close
• Genuinely useful for both distant subjects and macro-style close viewing in one unit
• Very light at 289g, easy to carry all day without neck fatigue
• Smooth, precise focus wheel
• Tripod-compatible for steady macro viewing
• Low price relative to the unique capability it offers

Cons

• Small 2.5mm exit pupil struggles in low light (dawn, dusk, shaded woods)
• Shallow depth of field at minimum focus means any hand shake throws the image out
• Short 15mm eye relief may be tight for glasses wearers
• Narrower field of view than full-size compacts, making it less ideal as a primary birding binocular for fast-moving subjects
• Non-lockable diopter ring

Who Should Buy This

This is the right call for naturalists, butterfly and insect enthusiasts, macro photographers scouting subjects, and hikers who want one small optic that can both glass a distant peak and inspect a wildflower or caterpillar up close. It’s not the binocular to buy if your priority is serious low-light birding or you need the widest possible field of view for tracking fast raptors — a standard 8x32 or 8x42 will beat it there every time.

Verdict

The Papilio II 8.5x21 does one thing no other binocular in its class does — focus down to 1.65 feet — and it does it well enough that naturalists and butterfly watchers keep recommending it years after release. It’s not a great all-around birding binocular, but as a lightweight, affordable dual-purpose tool for trail use and close observation, it earns a 7.5/10.