Introduction
I received an unusual PENTAX Papilio II 6.5×21 binoculars for testing. I have been interested in these binoculars for a long time, so I started testing them with interest. It is unique in that it allows you to focus at a distance of only 50 cm from the subject. This feature can be interesting for the study of various small objects, insects, plants, museum exhibits, etc. A special lens shift mechanism is also declared, which allows you to see a single field of view without double vision when examining close objects. An aspherical element is declared in the eyepieces to reduce distortion. The belt has a quick release design. In addition, the binoculars themselves are light and compact, and due to the small magnification and good ergonomics, the image is very stable and shaking of the hands is practically not felt.

Declared technical characteristics:
SKU: 62001
Type: binoculars with a central focusing mechanism and “porro”-prisms made of BaK4 glass
Objective lens: 2 elements in 1 group
Eyepiece lens constructions: 5 elements in 5 groups (note: aspherical element declared)
Magnification: 6.5x
Objective lens diameter: 21 mm
Angle of view actual: 7.5° (note: lettering on the case)
Linear field of view at 1000m: 131m
Exit pupil: 3.2mm
Eye relief: 15mm
Relative brightness: 10.2
Diopter adjustment range: +/- 4 D
Minimum focusing distance: 50cm / 0.5m
Eyepiece Ring: Helicoid Type
Height: 55mm
Width: 110mm
Depth: 114 mm
Weight: 290g
Waterproof: no
Accessories: tripod adapter U (69552)
Prism coating: BaK4 (note: this is not a coating, but a prism material)
Lens coating: multilayer coating of all optical elements
Minimum focusing distance: 0.5m
Twilight factor: 11.7
Interpupillary distance: 56 – 74 mm

Package and body
I got the binoculars without a box and a belt, but with eyepiece covers and a case (demo version).
The body of the binoculars is made of durable plastic with rubber “armor”. At the bottom there is a thread for a 1\4″ photo tripod. The size of the binoculars, depending on the interpupillary distance, can vary from 111 x 115 x 56 mm to 91 x 115 x 66 mm. The weight of the binoculars with covers and a cover is 351 grams (binoculars 293.6 g, cover 8.1 g, case 49.7 g). Case made of synthetic leather, with a hole for a belt, size about 130 x 130 x 66 mm. The binoculars have no front covers, so it is better to transport them in a case. The country of manufacture is indicated at the bottom of the binoculars (China ).

The binoculars are not waterproof, do not carry out observations in the rain, fog up the optics, or drop them into the water. Before bringing the binoculars from the cold to a warm room, I recommend closing the eyepieces with lids and hiding them in their own case or a sealed bag / bag. Protect binoculars from impacts, falls and mechanical damage – this applies in general to all binoculars.

Mechanics and focusing
The mechanism for changing the interpupillary distance is atypical – the lenses themselves remain stationary, the eyepieces with the prism unit are displaced, and at the same time. The measured range of interpupillary distance is 56-74.5 mm, which corresponds to the declared one.

Due to their small size, a special grip is required to hold the binoculars – the fingers of one hand should cover the fingers of the other hand. There are thumb rests on the bottom of the binoculars. Thanks to the rubber coating, the binoculars sit firmly in your hands and do not slip out.

 

Focusing is carried out by a plastic ribbed drum 17.9 mm in diameter. Full drum stroke – 3 turns, rotates very (even too) easily. When focusing, the lenses are displaced both along and across the optical axis. Apparently, this is the special mechanism for preventing ghosting when viewing objects at close range. Additional diopter correction is carried out by rotating the right eyepiece, and with clicks and fixation, that is, it will not work easily and imperceptibly to knock off the focus of the right eyepiece. No channel desynchronization was detected; when focusing “back and forth”, the diopter correction of the right eyepiece is not disturbed, and there is no backlash either. The focuser is very responsive, but it works with the slightest touch. The measured minimum focusing distance was 0.58 m, which almost coincides with the declared one.

The body of the eyecups is metal on the inside, rubber on the outside, diameter 34.5 mm. There are three positions (screwed in, middle position, unscrewed) with lock and click.

There are adjusting screws, they are under the rubber “armor”, however, without sufficient qualifications and an urgent need to climb into the adjustment, I do not recommend. If your Pentax binoculars double – contact the official service center.

I personally have practically no questions about the mechanics – it is gorgeous, everything is thought out to the smallest detail. The only caveat is that focusing is too easy, but for some it can be both a minus and a plus.

Optics
The binoculars have a 6.5 x 21 formula, that is, the manufacturer claims a magnification of 6.5x and an aperture (lens diameter) of 21 mm.
The front of the binoculars is protected by plane-parallel glass with green coating, then there are two-lens objectives (blue coating), a block of prisms (green coating) and eyepieces (green coating). All optical surfaces bordering on air are coated.
Unfortunately, it is impossible to directly measure the aperture of binoculars without disassembling, but an indirect measurement using a digital caliper showed a value of 21.6 mm.

To determine the aperture, I decided to conduct a “test with a flashlight”: the binoculars are focused to infinity, a flashlight shines from the eyepiece, a light circle is projected from the side of the lens, the diameter of which is measured using a caliper or camera matrix (in specific testing – Canon 5D Mark II). This is exactly the working aperture. The flashlight test detects hidden aperture or aperture clipping by internal elements. The aperture measured in this way was 19.3 mm. Also, the aperture is partially cut off from one or two edges by prism blocks. Due to the aperture diaphragm, the brightness of the picture may decrease by about 20%.

The exit pupil is a light circle at the exit from the eyepiece at a certain distance from the eye lens, in fact it is an image of the objective (aperture). By projecting the exit pupil onto a sheet of paper or onto a photodetector matrix (in specific testing, the QHY5III178m camera), you can measure the exit pupil size. Testing with the QHY5III178m camera showed an exit pupil size of 2.87 mm (focus at infinity). There is also parasitic glare near the exit pupil.

To measure the magnification, two images of a ground object were taken – through binoculars and without binoculars. Then the size in pixels of an object in the field of view in each of the images is determined, we divide one by the other and get the multiplicity. For the PENTAX Papilio II 6.5×21, the magnification measured in this way was 6.7x.

Knowing the magnification and size of the exit pupil, you can calculate the working aperture – it is 6.7*2.8=19.2 mm, which agrees well with the test using a flashlight (19.3 mm).

The diameter of the eye lenses of the eyepieces is 14 mm, the lenses are recessed 2.7 mm relative to the eyecup. The measured field of view was 47 ± 0.4 degrees. The measured eye relief is 14 ± 1 mm. With glasses, you can see the entire field of view, but literally at the limit.

Image
Daytime testing of the PENTAX Papilio II 6.5×21 binoculars showed that approximately 30-40% of the field of view (from the center) is clear, then a gradual degradation in sharpness begins due to the curvature of the field and astigmatism (see previous photo). Chromatism on the axis is imperceptible, but along the field there is lateral chromatic aberration. The edge of the diaphragm is colored blue. There is also a slight pincushion distorsia. Due to the fact that the stereo base of the binoculars is less than the interpupillary distance, the 3D effect is weak when observing distant objects – the image is “flat”, but for observing close objects (less than 3 meters) this is even a plus. There is a slight double vision of the field diaphragm in the macro mode – two circles with a field of view do not completely converge into one; when observing an object at infinity, this effect is absent.

The binoculars have excellent collimation, the eyes do not get tired even from prolonged observations.

There is color distortion (pink tint). This is in good agreement with the stated light transmission graph (falloff in the area of green rays):

When tested at night, the stars at the edge of the field of view look like arcs (parallel to the edge of the field of view), and with a slight refocusing they turn into “sticks” (from the center to the edge). From memory, the PENTAX Papilio II 8.5×21 provided better image quality across the field, but the image was noticeably darker. Despite the small aperture, the binoculars are quite suitable for exploring the constellations, bright objects of the Messier catalog (M 45 Pleiades, M 42 Orion Nebula, M 31 Andromeda Nebula, etc.)

Summary
+ Lightweight
+ Compact
+ Focusing from 50 cm
+ Glasses show the entire field of view
+ Excellent mechanics
+ Excellent collimation
+ Fully coated optics
+ Thread for photo tripod
+ Low distortion

– Working aperture is less than declared
– Clipping of the light beam with prisms, reflections near the exit pupil
– Color rendering distortion
– Degradation of sharpness from the middle of the field of view.

The PENTAX Papilio II 6.5×21 is a lightweight and compact binocular with a unique macro focusing function. In my opinion, this is a great option for constant carrying in a bag or backpack, for daytime observation of insects, birds, landscapes. A small, but at the same time sufficient for most types of observations, the magnification allows you to achieve a stable image. Large range of interpupillary distance adjustment allows both adults and children to use binoculars.
Despite some shortcomings, I liked the binoculars very much – the formed image is pleasing to the eye, and its macro capabilities are generally out of competition.

You can buy PENTAX Papilio II 6.5×21 binoculars in the RICOH online store.

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