Pentax 20x60 PCF WP II

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rlow
Posts: 2347
Joined: Fri Oct 31, 2003 7:36 pm
Location: Jurong

Pentax 20x60 PCF WP II

Post by rlow »

INTRODUCTION

I have been looking for some time to get a higher-powered binocular to complement my Nikon Monarch 10x42 DCF roof prism binocular. My selection criteria are: 15-20x magnification & 60-80mm objective aperture, waterproofed, good eye-relief, gives sharp high-contrast images, preferably tripod mountable, preferably lightweight, within USD$250. I may also give preference to getting one from a local dealer as it will be easier to check whether the bino is well aligned/collimated. I have considered some models from Stellarvue, Garrett, Oberwerk etc but this model so happens to be recently made available locally. I bought it from Shriro, who are the new local agent for Pentax, and it cost $340 SGD.

STATED SPECIFICATIONS

Type: 20x60mm Porro-prism, center focused type
Dimension: 224mm(L) x 195mm (W) x 85mm (D)
Weight: 1400g
Waterproof to JIS Class 6 standard; nitrogen filled
Full bodied rubber armour

IPD: 57-72mm
Diopter Range: +/- 4m
Focus Range: 8m to infinity
Eye Relief: 21mm
Exit Pupil: 3mm

Fully Multicoated Lens & coated Bak-4 glass prisms
Objective Lens: 2 elements in 1 group
Eyepiece Lens: 5 elements in 4 groups
AFOV: 44 degrees
TFOV: 2.2 degrees

FIRST IMPRESSIONS

I got my Pentax 20x60 PCF WP II yesterday. I tried it out last night and here is my first impression:

Apart from the binocular, the whole package comes with two separate black objective lens caps, one integral elongated black plastic cap to cover both eyepieces (unfortunately, this is quite loose, I will have to add some felt or velvet to get a proper friction-tight fit), a basic neck strap and a slim black PVC/fabric softcase that seems just barely adequate.

Physically the 20x60 binocular is not too huge compared to a typical 20x80, in fact it is only slightly bigger in size than a typical 10x50 porro-prism bino! With the moulded finger groove, it fits my hand well for a firm comfortable grip. I think it would be nice if the central ridged focus wheel could have been slightly less stiff, though some may say that this is typical of waterproof binocular. After I achieved focus and focus-lock on the stars, I would then transfer my hands to hold the objective ends for a steadier hold, and the 60mm objectives are comfortable to grip. I weigh it on my calibrated digital gramscale and it is 1382g. The overall black rubberised finish is neatly done and looks presentable. There is an embossed unpainted rubberised 'Pentax' lettering sticking out of the rubberised barrel.

I have no problem getting a comfortable eye spacing with the inter-pupilary distance (IPD), and correct diopter adjustment with my glasses on. The diopter adjustment on the right eyepiece has two extruded ridged finger grips and smooth click-stop motion, which allows for a controlled small-increment focusing. The eye cups are firm rubberised helicoid types which has three click-stop positions. The eye-relief is stated as 21mm and the eye lens are flushed with the eyepiece body. I find that with my glasses on, the middle position of the eye cups is best for getting the full field of view without black-outs. At the lowest position, I tend to get a partial black-out. The highest eye-cup position is good and comfortable for viewing without glasses. I find it convenient to view with glasses on, as I would first view the sky with my naked eyes with glasses on and then look through the handheld binoculars. I have no problem locating objects with this binocular in spite of the narrow 2.2 degrees actual field of view as I am familiar with telescopic star-hopping. Your mileage may differ. I am also quite comfortable using this binocular handheld without support for short periods of time, though I find that some form of support always give me a steadier view with more details visible, eg, being able to observe the two equatorial belts of Jupiter. I have no problem using my Slik L-shaped binocular bracket to mount the binocular to a standard camera tripod, by mounting the bino upside down.

The binocular lens are stated to have full multi-coatings. The lens coatings are evenly applied without any streaks. All lens surfaces appear dark green when viewed from an angle. When viewed straight on, it is dark and it doesn't seem to have any reflections and the image of my face is dark and hardly visible. The interior of the binocular is evenly matt-black. Unfortunately, the objective lens are not edge-blackened. The prisms seemed to be properly aligned and well-finished, and it does not seem to intrude or vignette the light path.

The exit pupils appeared bright and perfectly circular, without any edge dimming, clipping or faceting. The binocular alignment is excellent for my binocular, as I am able to form a perfectly circular images that appeared aligned. I tested by covering the objectives on and off alternately and I was unable to visually detect any vertical or horizontal misalignment at all. My eyes are sensitive to misalignment and I had to reject three Nikon Monarch 10x42 binoculars before I got one that has good alignment.

Apart from the limited 44 degrees apparent field of view, the image quality is excellent. I observed that the focused stars are sharp on axis (the focused airy disk is tiny and without spikes) and also sharp almost right to the edge (>95%) without any visible evidence of field curvature, coma, astigmatism or distortion. I found out that this is because Pentax has incorporated field-flattener lens at the eyepiece end. Contrast is very good as the sky background is dark, the edge of the image is sharp and it is black outside of the image. However a bright light just outside the edge of view did introduce some flaring into the image. CA is faintly visible on bright objects but it is not objectionable to me, since I intend to use it mainly for deep sky observing anyway.

I plan to do more extensive testing of the binocular this weekend and maybe try to compare it with a 20x80 binocular.

UPDATE 1:

Last night, I look through my 20x60 again at the stars, and I did detect very slight dimming (less illumination) at the outer 10% edge of field. This is very subtle effect visible only when I purposely look for it and it did not diminish my enjoyment and use of this binocular. Though I am not an expert in this field, but from my three decades of binocular observing and two decades of telescope observing, I am of the opinion that this effect I saw does seems to be due to vignetting. Also, looking through from the objective edge, I could see that slightly less than 50% of the exit pupil is illuminated.

I measured the objective aperture and it is exactly 60mm clear diameter. The interior wall finish is smooth, matt black, non-reflective and without any baffle rings or ridges. The prism housing has a slightly smaller clear circular field stop and there are three prism edges just barely visible in the front prism (very close to the prism housing edge), also another prism edge is visible in the second prism (again very close to the housing edge). This happened to quite a few other binoculars that I have seen. To check for any vignetting due to the prism field stop, I look through from the objective edge and I could see about 99% of the prism field stop diameter, except for a tiny sliver of the edge nearest the objective edge that I viewed from. So far I have enjoyed the views and I like the image quality using this binocular, so I won't be too concern whether the prism are undersized or undercut or not.

UPDATE 2: COMPARING 20X60 TO 20X80

Last night 01 Jul 06, 5am local time, after watching the Bleus beat the Yellow Greens, I took the Pentax 20x60 and the 20x80 out for 45 minutes for a quick-look comparison. Here is a few of my first impression comparing both binoculars:

Kindly note that the 20x80 was borrowed from my friend, who said it is a prototype model that is apparently of a different design from the production model, so my observation notes below is intended just as a general comparison between the Pentax 20x60 & a typical 20x80 binocular only. Also, I would like to say that I am not affliated, bias for or against, or have any commercial interest in either Pentax or their agents/dealers.

Physically the 20x80 is much bigger (340mm by 220mm) as compared to the Pentax 20x60 (225mm by 195mm). The 20x80 is also heavier (2182g compared with 1382g) and, unlike the 20x60, I am not inclined to handhold and focus the 20x80 as the longer barrel and bigger objective lens makes it rather front heavy and unbalanced.

I mounted each of them on a separate tripod side by side and compared the same image back and forth between both binoculars.

The sky condition last night was poor: with local light pollution, poor transparency and some cloud cover, only a few bright 2nd mag. stars can be seen with the naked eye. Nevertheless, I just wanted to do a quick comparison on some stars, and plan to do more comprehensive comparisons on better nights.

The 20x80 seems to show good alignment on-axis, though the alignment appeared slightly off horizontally when I viewed the extreme edge of field. The stars in both eyepiece appeared quite sharp on-axis with small radial spikes from 12 o'clock to 5 o'clock position. The sharpness falls off quite badly (details are lost) at about 50% towards the edge and it gets worse from about 75% to the edge. The apparent field of view is about 60 degrees, and overall, the image is quite pleasing.

The Pentax 20x60 gave good alignment on-axis and also at the edge. Stars focused on-axis are very sharp and the focused airy disk is obviously much smaller without any radial spikes in the Pentax 20x60 compared with the 20x80. (Earlier that same evening, I was using the Pentax 20x60 with three of my friends and we were able to resolve Saturn's ring separately from the planet. The two equatorial belts of Jupiter can also be seen.) The airy disk enlarged slightly at about 60% towards the edge but it is still sharp, and this image quality holds out until very close to the edge (>95%), where it becomes a bit more enlarged. The interesting thing is this: the airy disk at the edge of the Pentax 20x60 is still smaller (and sharper) than the focused airy disk on-axis in the 20x80!!!

The apparent field of view in the Pentax 20x60 is narrow at only 44 degrees. I noted interestingly enough that I can see three sharp stars at the edge of field forming a wide equilateral triangle in the Pentax 20x60 but in the 20x80, the three stars are nicely framed but as they are just outside the 50% sharpness towards the edge, the three stars are not sharp at all!

The stars and especially the background sky is a bit brighter in the 20x80 than the Pentax 20x60. This is to be expected due to the increased light gathering power and larger exit pupil of the 20x80. However the visual contrast in the Pentax 20x60 is much better. I tried to seek out the fainest star visible in both binoculars and so far there are no faint stars in one bino which I could not see in the other. In fact, it was easier to use direct vision to see a faint star in the Pentax 20x60 than the 20x80. It seems to me, from this initial comparison that the better contrast of the Pentax 20x60 has somehow compensated for the difference in aperture between 60mm and 80mm. However, I would say my result is still inconclusive as the sky transparency is poor and the comparison is just on single faint stars. Also, I have not compared on double stars, clusters, nebulae or other deep sky objects.

One point I noted was that the Pentax 20x60 used in urban skies suffered from some flaring on one side due to stray light coming in from a nearby street lamp. This reduces the visual contrast. Shielding the objective with my hand temporarily eliminated the problem, so I will have to improvised a pair of light shields/dew caps for future use. This flaring did not seem to occur in the 20x80 although both are side by side pointing 45 degrees at the same object. I found out that the baffle ridges in the 20x80 barrels probably helped in scattering out the stray light; the Pentax 20x60 have barrels which are smooth matt black that probably reflected in the stray light entering the binocular.

This morning, I used my venier caliper to measure the exit pupils of both binoculars. To minimise errors, I keep the caliper square on and next to the eyepiece lens, took ten measurements at various angles of the exit pupil for each eyepiece, discard the two extreme readings, and average out the result. The 20x80's exit pupil is measured at 4.0mm, while the Pentax 20x60's exit pupil is measured at 3.4mm!

To summarize, here are the main points as follows:

PRO:
1. Small Size & Weight - can handhold, highly portable, only small mount/tripod required for a steadier view.
2. Good Ergonomics - comfortable to hold, adjust & focus.
3. Good Eye Relief - comfortable to view, full FOV visible even with glasses on.
3. Good Built Quality - rubber armoured, waterproofed, nitrogen filled.
4. Good Optical Quality - FMC lens, Bak 4 prisms, good collimation
5. Good Image Quality - very sharp on-axis resolution, good contrast, no distortion, good edge quality

CON:
1. Narrow AFOV (44 deg) & TFOV (2.2 deg) - gives tunnel-like view, harder to locate objects, cannot get wide field view.
2. Very slight vignetting - not significant to image quality.
3. Slight flaring due to stray light - can be eliminated with light shields.
Last edited by rlow on Tue Jul 11, 2006 2:06 pm, edited 13 times in total.

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VinSnr
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Joined: Sun Sep 28, 2003 7:01 pm
Location: Andromeda Galaxy

Post by VinSnr »

Rlow, good review! The only thing is, you didn't mention where you bought them.

I have tried several Pentax PCF WP before (those 10x50 and 7x50 models...not this one you have) at the shops around Lucky Plaza and Sim Lim and while they were really sharp, a few of them that I tested had alignment problems. Your testing is correct...by covering the objectives on and off and the ones I tested had some horizontal and vertical misalignment. I was quite surprised with that.

But good to hear that you found one that is excellent. I am pretty sure you will enjoy this bino for some quick sweep around some clusters. I still remember my first view of Halley's comet in 1986 was with just a 8x30 bino.....wonderful view to behold.

Enjoy! and do post some photos if you can.

User avatar
rlow
Posts: 2347
Joined: Fri Oct 31, 2003 7:36 pm
Location: Jurong

Post by rlow »

Thanks Vincent.

I bought this from Shriro, who are the new agent for Pentax.

Currently I am unable to post photos at the moment, sorry; I will try to do so another time.

We will be comparing this 20x60 with a 20x80 bino, with three other Singastro guys tomorrow evening on our Malaysia recce trip; let me know if you or anyone else would like to join in.

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