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Vixen Apex Pro 8x42 roof prism binocular Mark Vints introduction There comes day when you find yourself away from home with an unexpected viewing opportunity. Likely conditions are better than in your backyard. Just by chance you haven't thought of bringing your favorite astro gear, or possibly a need to travel light prevented it. If this hasn't happened to you yet, I am sure that one day it will. Happened to me a couple of times... Then I decided to act on it. My favorite astro gear to take along on trips would be my 80 mm refractor and my 20x80 binoculars. These are pretty compact by my standards. But they still are too bulky to take along on say a three-day business trip. For those occasions my first choice would be a smaller pair of hand-held binoculars. My Swift Audubon 8.5x44 porro would be a great tool for this task. It still is too bulky to fit into a briefcase or coat pocket though. My little Leica 8x20 on the other hand is truly pocket size and reaches 3 magnitudes beyond my naked-eye vision! It never ceases to amaze me what it shows me on the night sky. But it cannot break the laws of physics ? there's only so much you can expect from two 20 mm apertures. Whatever replaced it would also have to be at least as good at daytime viewing. So I decided I wanted something larger than my 8x20 and more compact than a typical 40-50 mm porro binocular. A roof prism binocular was the logical choice since these are more compact than porros of the same aperture. I knew I wanted a decent mid-level model with phase coatings for optimal performance. Anything really expensive would mostly sit unused for fear of damaging it. I also wanted something I could check out in a store within reasonable driving distance. I studied websites and specifications for quite a while. In the end I narrowed it down to an 8x32 Pentax DCF SP or Vixen Apex Pro. time to go shopping The store I visited carried a nice collection of various brands, including Vixen, but not Pentax. It took me less than 30 seconds to realize that the weight and size difference between 8x32 and 8x42 roof prism binoculars is not that significant. So I upgraded my wish list to an 8x42 which after all has 72% larger objectives than an 8x32. For astronomy this makes a significant difference in light gathering ability. Also the larger 5.25 versus 4 mm exit pupil is an advantage by giving a brighter night-time view. On the downside, an 8x32 would typically have a larger field of view than an 8x42. The Vixen Apex Pro 8x42 I tried that afternoon immediately convinced me with a bright sharp view and good ergonomics. Vixen's website says this Apex Pro series is the best they can currently produce in roof prism binoculars. Sharpness and edge sharpness were checked by looking at fine print across the street. Edge sharpness in these conditions was excellent and by itself sufficient to convince me to purchase them. Brightness in daytime viewing is mainly determined by light transmission rather than exit pupil. This is because in bright light the eye pupil is smaller than the typical binocular exit pupil. So I found it a relevant comparison to put the Vixen 8x42 up against a Swarovski 8x32 EL. The Swarovski won by a difference I would describe as just visible. Still the Vixen 8x42 is in no way dull or dim. Later I would compare it to a Chinese-made "fully broadband multicoated" 8x56 porro, and this latter one really was dull in comparison. As I said I found the handling and ergonomics pretty good. Focusing is responsive with just the right resistance. Diopter adjustment on the right eyepiece is a nice stiff ring that keeps its position when you accidentally brush against it. The rubber-coated exterior is very grippable and the body shape fits my hands remarkably well. I like that they have twist-up rigid eyecups even though they miss intermediate clicks. The overall impression is one of solid build quality and excellent fit and finish. One comment on the ergonomics is that the focus direction is opposite to my other binoculars. To focus closer you turn the focus wheel to the right. Not really a problem for me. specifications The Vixen Apex Pro 8x42's basic specifications are: - phase coated prisms; all optical surfaces are hard multicoated - water proof (no spec on how deep) and nitrogen-filled - true field of view = 6.5-deg (114 m at 1000 m) - eye relief = 19 mm (not verified) - IPD range 58 to 74 mm (no scale; need to set on sight or with a ruler) - weight = 705 g (25 oz. for US readers) - dimensions at 70 mm IPD setting: 147 mm long, 124 mm wide, 55 mm deep - closest focus = 3 m specified, 2 m tested - tripod socket with screw-on cap - aluminium housing with rubber exterior The 6.5-deg FOV at 8x magnification means that these have a 52-deg apparent field of view. It has been many years since I last owned a binocular with AFOV this narrow. My workhorse binoculars in recent years have been 8.5x44 and 20x80 from Swift, both having a 70-deg AFOV. The relatively narrow FOV in the Vixen 8x42 has not yet bothered me in the 6 months I've used it. I believe the two main reasons for this fact are that (i) the edge sharpness is remarkably good, and (ii) the field edge itself is the sharpest and blackest I've seen in any binocular. optical performance When I just bought them I optimistically estimated that the field of view is sharp to about 95% out towards the edge. Even beyond that the view doesn't get really ugly. The field as a whole is giving the impression of being sharp from edge to edge unless you really look for edge aberrations. Whatever Vixen did is working for me. The 'whatever' turns out to be the inclusion of an aspherical element in the eyepieces. There's a tell-tale reflection off the eyepiece which comes from this aspherical element. In subsequent more objective testing on the night sky I've had to revise my estimate of the sharp FOV to about 85% which is still quite good. This means just the outer 0.5-deg of the 6.5-deg FOV is somewhat unsharp, in other words the center 5.5-deg is sharp. The Moon is sharp when it is at least one lunar diameter away from the field edge. I've measured the apparent resolution at 0.5-deg from the edge to be 240 arc seconds. The target was the double star Psi-1 Pisci whose mag 5.6 and 5.8 components are 30 arc seconds apart. This is just one test on one occasion but still of interest in this context. The aspherical eyepiece element does have one unexpected side-effect. The very sharpest area where stars focus to the smallest points of light, is not in the center of the FOV but actually some distance away from it. I still rate the center as very sharp! It's just that a third to half way towards the edge stars are just a touch sharper still. In the inner 5.5-deg of the FOV there is a minor amount of field curvature. Most of the decline in sharpness can be focused out. The residual field curvature and the position of sharpest focus are just two peculiarities of the optical system. I would not rate them as deficiencies. They do lead me to the conclusion that the aspherical element could still be optimized. To get the very tightest focus on stars requires optimal eye positioning as it does in any binoculars. Setting the correct IPD is one important aspect of this. The other aspect which I see much less often mentioned, is where you place the eyecup rims against your face. Here the thickness of the rigid eyecups plays a role. I find I need to put them fairly high up towards my eyebrows or else I get asymmetrical flaring on the brighter stars. For this precise positioning it would have been nice to have intermediate stops in the twist-up eyecups. Eye placement also affects performance with regard to chromatic aberration (CA). In the correct position CA is virtually absent in the center of the FOV. Out towards the edges there is always some noticeable CA though. I can't really tell if this is severe enough to bother other people as sensitivity to CA is highly personal. With the clean center FOV I personally haven't been bothered much by the CA at the edges. A potential optical deficiency which personally bothers me a lot more than CA, is internal reflections on the Moon. The resulting ghost images really distract me. At the same time glare and flare are equally undesirable even if often better controlled. In this regard the Vixen Apex Pro 8x42 does remarkably well. It gives me the cleanest view of the Moon ? with one remaining minor issue which I'll get to in a second. But first let me comment that this Vixen is virtually free from out-of-focus ghosts caused by the Moon's image bouncing between the eye and the outer eyepiece element. This is something I really appreciate as it is actually the most bothersome reflection in a few of my other binoculars. That one remaining minor issue on the Moon is a typical one for roof prism binoculars. The top of the roof prism creates a diffraction spike and the two sides together result in a large 'X' cross pattern centered on the Moon. Now in all fairness it takes looking at a nearby streetlight to make this obvious. On the Moon I'd describe it as just visible. It depends a bit on the viewing conditions. On anything fainter than that it is invisible. For me it is a non-issue. One final remark is that this Vixen 8x42 is giving an obvious semi-circular glare when I get within 10-deg or so of a streetlight. This is perhaps the one optical performance aspect I'd have Vixen improve on in this binocular. On the other hand I suppose I could easily fashion a couple of 'dew shields' extending 5 or 10 cm from the front. I haven't noticed any glare problems so far in daytime viewing. left to right: Leica 8x20, Vixen 8x42, Swift 8.5x44, TS 7x50, Swift 20x80 caps, case and straps Next to the performance characteristics there's a few points to make on the 'extras' that come with these binoculars. The objective covers are of the push-in type and fit nicely with no slop whatsoever. Their rim extends about 1 mm beyond the outer diameter of the objective barrels. This unfortunately is sufficient to have them slip off when getting the binoculars out of their tight-fitting padded soft case. On the eyepiece side I notice that the eyecups are slightly conical. I'm seeing more and more of these come on the market. It does not take a degree in physics to realize this shape has to result in difficulties getting a secure fit with any covers. A friendly dealer fortunately improved the situation by placing a few pieces of adhesive-backed felt on the inside of the eyepiece covers. It's still only just sufficiently working. Again the main issue is with the soft case being so tight. By now you've understood the soft case is a tight fit. As such I think that is a good thing, however it clashes with the caps as described. The neck strap is just a bit too short. Or rather the thick hard pieces of leather connecting the wide center part to the narrow outer parts are too high up. Or it could just be that my neck is... you get the picture. I may replace it with the superb wide cloth strap that came with my Swifts. This one is longer and softer and feeling much better. use on the night sky So after all this talk of characteristics and properties, how do they perform as a tool for astronomical viewing? In my typical mag 5.5 skies just about any binocular will show an interesting view of showcase targets such as the Pleiades (M45), Praesepe (M44), the Perseus Double Cluster, the Andromeda Galaxy (M31), open cluster M35 in Gemini, etc. (without forgetting the Moon). What a binocular has to do for me in order to be 'astronomy-capable', is opening up some of the sky that lies beyond these showcase objects. The Vixen Apex Pro passes this test with flying colors. A few recent examples from my backyard: - it shows me M81/M82 with relative ease; - NGC 2158 is a nice hazy patch right next to beautiful M35; - it begins to resolve stars from the background glow in favorite clusters such as M36, M38, M67, NGC 1528, NGC 7789. In slightly better skies (mag 6.0) it shows the North-America nebula and Veil nebula. In those conditions, scanning along the Milky Way is pure joy. In October 2006 these Vixen 8x42 accompanied me on a business trip with an itinerary that "coincidentally" allowed me four nights at remote locations in the Alps. OK, I cheated and also took the 20x80, but that's another story. Sky conditions on those four nights were exceptional for me. The naked-eye limiting magnitude reached close to 7.0 on the first two nights, and still above 6.5 on the last two. Here are some of the notes I made from what I saw in the 8x42: - the North America nebula is stunningly bright, completely defined and detached in the 8x42. All its borders are clearly visible. The neighboring Pelican nebula is visible too, though much dimmer and less well defined. Many, many dark and bright clouds north from here towards M39 and beyond. Many clusters also; - the Veil Nebula just pops into view when the 8x42 is aimed at it. Viewing the Veil in the 8x42 draws the view towards several large rich open clusters more towards the center of Cygnus. From there I'm drawn to the incredibly rich star clouds intermingled with bright nebulosity that make up the core of the Cygnus Milky Way; - M11 in the 8x42 gives me a great impression of its "wild duck" fan shape. The cluster is well resolved. The Scutum star cloud is bordered by some of the most spectacular dark nebulosity to be found; - the slanted E-shaped dark nebulosity (B142+B143) west of Altair is very prominent; - M33 is visible to the unaided eye. In the 8x42 it is obviously bright and large; - M31 is about 3.5 degrees long and the dark lane on the north side is well defined. I am almost shocked at how large its satellite M110 is; - not knowing precisely where the Helix Nebula is, I pick it up easily by just sweeping the sky in Aquarius. It's huge! It also appears not completely round but more irregular in shape; - Ursa Major is hugging the northern horizon. M81/82, M51 and M101 are still obvious targets easily within reach of the 8x42. M81 strikes me as being much larger than usual: the fainter outer area has come into view. M101 surprises with its nice and well-defined round shape and brightness; - I take my first shot at IC342, and see it clearly in the 8x42 as a rather faint and ill-defined diffuse nebula. This thing is big! - I make my 1000th attempt at seeing the nebulosity in the Pleiades, and IT'S THERE!! A bit disappointed that it isn't more like the long exposure photographs... Still this would have to be one of the major milestones in my 29 years in astronomy; - the Perseus double cluster is spectacular beyond words. This target unlike any other gives me the impression of being a "tip of the iceberg". As the conditions improve more of the iceberg becomes visible. This time the entire area grows into a "Perseus star cloud". To the east it is bordered by a large long dark area swooping down from Cassiopeia. Nearby Stock 2 is losing it's typical "Muscle Man" shape. The area in between the 'arms' fills up with stars ? it now looks more like a mushroom. A bit farther east, I see the nebulosity complex around Mel 15; - the Orion nebula is as impressive as expected. A bit further north the Flame nebula is visible. On that same trip I also had the opportunity to compare my Vixen 8x42 to a top-quality 7x50 porro (the TS 7x50 MX which I bought just for this purpose). I chose the following targets for a shoot-out: North-America nebula / Pelican nebula / Veil nebula / M101 / the nebulosity around Mel 15 / M31 and its satellite M110 / Helix nebula / Merope nebula / M33 / the dark nebulosity in Scutum, Aquila and Cygnus. On these 11 targets, there were 5 where the 7x50 had the edge, 5 where the 8x42 showed a slightly better view, and 1 tie. Let me add that my eye pupils do (just) take in the 7.1 mm exit pupils from the 7x50. My conclusion is that the compact 8x42 packs quite a punch at half the size of the 7x50. in conclusion My overall conclusion is that the Vixen Apex Pro 8x42 is a high quality instrument capable of satisfying the discriminating amateur. Also for a typical "birding glass" it does quite well at showing the wonders of the night sky. Most importantly, it fills perfectly that niche I had for a compact travel binocular capable of quality day- and nighttime views. I have absolutely no second thoughts on this purchase. When I brought them home, my wife glanced as if to say "did you really need that?" When I convinced her to take a look through them, the ergonomics, viewing comfort (she wears glasses) and optical quality won her over instantly. She commented that "these are as good as your telescope" (an 80 mm apo). Highest praise I've ever had from her on any binocular. This is a very good binocular at a still-attractive price level (about 450 euro). You'd think these would sell like hotcakes and be available everywhere. I don't know how they're selling, but I can comment on the availability. As far as I have seen they are not marketed in the US. Some searching around on the internet showed me that betterviewdesired.com has a review of the Celestron Regal LS which look largely identical. In the UK they appear as the Avian F from Ace. I've also recognized them in a previous version of the Kite Forster. Let me know if you find other 'clones'. Mark Vints March 2007