I recently bought a pair of NOS 10x40 BPO/Baigish porro prism binoculars. The weather had been poor but yesterday daytime and evening and this morning I've had a chance to use them and test them and it may be the best binocular I have ever used.
Holger Merlitz reviews the BPO/Baigish 10x42 rubber armored military waterproof version of this binocular at his website www.holgermerlitz.de and most of the things that he says are the same. It is likely the sharpest binocular he has ever seen or used as well and is much sharper than even the incredibly expensive or historically renown porro prism or roof prism binoculars I tested it against or he has seen as well. I tested this binocular against a very wide variety of 10x binoculars of widely diverse types. It was nearly as bright as the 10x50s I compared it to, and so much sharper than anything else it is peculiar. But there are 6 big differences between this Baigish 10x40 I bought and the BPO/Baigish 10x42 tested by Holger Merlitz (and most of those were for the better).
First of all the 10x40 version of this binocular is not waterproof. This is the only real drawback compared to the 10x42 BPO. In addition the 10x40 does not have individual eyepiece focus. The focus is via a center wheel and is ultrafast, easy to reach and then seems happy staying in position. The right eye diopter correction works well, adjusts quickly, and then stays in place. Some may prefer the fold down rubber eyecups used on the 10x42 model, instead of the relatively flat solid plastic eyecups on the 10x40 but if so, then there are various aftermarket rubber eyecups that will screw on or fit over the eye lens guards on the 10x40.
The most important difference I saw was that in the civilian 10x40 regular Deinstglass (flint glass) is substituted for the radiation-proof yellow glass that is used in the 10x42 and 7x30 military models. If anything, this improved the sharpness which was already astounding. Add to that the fact that this civilian 10x40 model is ultra-lightweight at about 1/2 a pound and it is like newly discovering an old world. I started watching in a feeding area on my nearest neighbor's property 500 yards, and could clearly enjoy the antics of some Canada geese that stopped in for a meal. The conditions were perfect with no heat waves and the geese being lit by the rising sun behind my back, but I would normally be forced to pull out a spotting scope to get such a sharp view at 10x (I have an 80mm fluorite spotter with interchangeable eyepieces and can get great 10x views with it).
The field of view was a tiny bit narrow but reasonable, and as Holger says, these are easily usable for people with eyeglasses to see the entire field. I compared these binoculars to my favorite 10x the 10x50 CJZ Dekarems from the middle 1980s, the Hensoldt Dialyt 10x50 military version from the late 70s, the Swarovski Habicht 10x40, my 10x35 Nikon EIIs, plus Zeiss 10x40 Classics, 10x42 Conquest FLs, Nikon 10x40 Superior Es and Nikon 10x42 Nikon HGs borrowed from friends. The fully multicoated surfaces on the Baigish 10x40 are nicely done and using mostly magenta/purple and yellow/gold/brown final coatings, the color rendition is absolutely neutral unlike the military model 10x42. In this regard they compared very well to the Dekarems, Habichts and the Nikon EIIs. These Baigish 10x40s are also extraordinarily bright. They lack the reticle in the right eye found in the military models and this helps the image brightness greatly.
The view through the Nikon Superior E 10x42s had been my all time favorite for sharpness edge to edge, but the Baigish 10x40 7 element eyepiece design with built-in field flattener easily surpasses it. I couldn't compare the Fujinon FMT 10x50 or 10x70 binoculars to the Baigish 10x40 because the friend who owns them is away, but I did pull out my 10x50 Williams 10x50 ED binoculars and a pair of 10x70 Nikon Astroluxe binoculars and compared them to the Baigish 10x40 in daytime only. The Baigish 10x40s were sharper with a bit less brightness. At night these other two binoculars, the Hensoldt 10x50 Dialyts and the 10x50 Dekarems were better in the center of the field when looking at diffuse star/nebula sky areas, but checking the moon there wasn't much to choose from except the sharpness and stereo-illusion of the Baigish makes you feel like you are "on the moon" instead of just looking at it.
It is surprising that so few of the 10x40 Baigish binoculars are sold for birding. They are super sharp, with great depth of field, contrast and stero-optic impression. They are ultra-lightweight and well balanced, with a large eye lens that can be used with or without eyeglasses. I had always wanted a pair of Nikon 10x42 Superior E binoculars but couldn't justify the price, and even though the Zeiss Conquest 10x42 FL is also nice it isn't sharper or brighter than the Baigish 10x40. This Baigish 10x40 isn't perfect and the case and strap included are pretty simplistic (I wouldn't use the strap but I put on a wide soft strap that's easy on the neck and it works great because the low weight never gives me any soreness or fatigue). I thought it might be harder to acquire one of the hawks or turkey vultures we have constantly prowling the airspaces above the local ranches because of the narrower field of view compared to the 10x50 Dekarem, 10x50 Dialyt or the 10x50 Tasco International 420s I often use, but the Baigish 10x40 "points" so quickly and easily, that I acquired both of these birds riding the currents, with ease.
I much prefer this model Baigish 10x40 compared to the 10x42 BPO which is made by the same company. Baigish also makes a civilian 8x30 that looks quite similar (and is also super-sharp) and a 12x45 with a similar finish that is a slightly older design. The BPO 7x30 is one of their current military design products with a great reputation and it is very good too if you want sharpness, ruggedness, and waterproofing in your binoculars binoculars, but the price you pay is the yellow tint that is quite obvious if you compare the 7x30 with other binoculars switching back-and-forth. In one of those "Wow" moments I experienced with the Baigish 10x40s, I became excited about "re-seeing" birds, foxes and all the other animals and plants that I've become so blase` about when viewing them with other binoculars.
What I wonder about is why the maker of this binocular doesn't hype their super-sharpness, incredible contrast and super-brightness to the sky with the ultra-low weight being a big plus as well. The Leupold 10x42 Gold Ring HD is very very good and not the most expensive binocular on the planet and they promote their sharpness constantly, as do Nikon with the 10x42 Superior E and Zeiss with the 10x42 Conquest FL etc. etc. The 10x40 Baigish is as good or better than any of them and yet I can't remember seeing a test or review of this product (although the Holger Merlitz review of the 10x42 BPO/Baigish is close). I am glad I got mine and have already put it on the "shelf by the door" to grab when there is something to see, during reasonable weather. I'll take a Leupold 10x if it's raining, but the 10x35 Nikon EII just got displaced and that is a remarkable accomplishment. I'll still use the bigger aperture binoculars for star gazing, but at this point, I think the Baigish 10x40 is about the sharpest 10x binocular on the planet.
Can you provide photos of this binocular, and is this model available from any on-line retailers? I'm curious to look through these. I also have the 10x42 IF version that you mentioned. I consider it to be good, but not quite a match for the top-line 10x models in terms of center-field resolution.