Baader Maxbright Binocular Viewers - A Tale of Two Oculars
Submitted: Thursday, 7th March 2013 by David Roser
Binocular viewers promise an observer the opportunity to view the night skies in three dimensions. But in Australia they don’t seem very popular. This article outlines how I explored the strengths and limitations of this equipment, its costs, sources, pitfalls and technical issues and decided in the end to buy a mid-price range pair the Baader Maxbrights along with necessary accessories. It summarises the important issues raised in various blogs and recounts how my experiences in buying and assessing the Maxbrights corresponded or otherwise to the caveats and what information was missing from the various on line opinions. Finally I report the results of first light trials with my 3 telescopes, a 72mm Eon refractor, a 200mm CPC SCT Cassegrain and a 300 mm Dobsonian. In a nutshell i) the binoviewers worked very well in my hands and I would recommend them to any visual-only star gazer especially if they want to view the moon (wondrous), planets and bright stars (both impressive); but ii) with the proviso that while they should work very well with a tracking Cassegrain, and they are probably workable with a refractor, you could have serious problems with Newtonian optics. It all comes down to having relatively high focal length and a focuser with sufficient travel to compensate for the binoviewers adding 10 cm of path length that your telescope was probably not designed to cope with.
As a microbiologist I’ve used Zeiss, Nikon, Olympus and Leitz research microscopes with binocular heads routinely (trinocular actually as photography and video cameras are common). The difference in comfort over monocular microscopes is enormous. The binocular heads allow long periods of looking in wonder under dark field and fluorescence at views similar to the night sky. So I puzzled why binocular viewers are not more popular in Australia as evidenced by no equipment review in IceInSpace and no units for sale at my local collectables shop (Bintel Sydney).
Recently I bit the bullet and investigated binocular viewers prompted by the prospect of an improved viewing experience, decreased eye strain compared with a monocular and addressing that perpetual ‘star party’ problem – the difficulty novice telescope viewers have in switching from stereovision to monovision which no amount of cajoling can overcome (you win or lose them in a 10 second window). Also I was curious to understand the telescope v. microscope difference.
This review is about exploring the binoviewer information which a novice will encounter, and reviewing the Baader Maxbrights I finally selected. A digression - I’m not talking here about conventional binoculars or binocular telescopes, an extreme example of which can be seen here, but rather binocular viewing heads like those seen on microscopes which split a single beam allowing a kind of stereovision.
Finally the declaration - I have no financial interest in any products or suppliers identified. Nor did I start with any preconceived notions of what would work best. This narrative, however, reflects a series of rationalised choices. So to help the reader reach their own conclusions the decision process and input information is outlined.
Exploring the Binocular Viewer issues and options
Not being an astronomy club goer I get most practical information via Google searches, from on line reviews and from talking with the Bintel people when making a telescope purchase. Initial investigations suggested a range of technical complications explain why binocular viewers aren’t more popular and discussion is sparse – hence this review/analysis Nevertheless I was surprised at the limited availability, as a binoviewer sale should necessitate the purchase of additional matching eyepieces and filters.
Telescope Binoviewers v. Microscope Binocular Heads
Taking first the issue of telescopes v. microscopes: These two instrument classes were invented more or less concurrently in the 17th Century, have essentially an objective lens system, a front end optical tube and observing eyepieces at the rear, exploit diverse filter combinations and are used for analogous purposes (seeing things too small/faint for the naked eye). However, they diverge in several critical design and manufacturing features. Microscopes and their accessories are usually all purchased from a single manufacturer, so the optics tend to be harmonised. Also users, instead of having a collection of telescopes from different manufacturers with very different optical characteristics (refractor v. Newtonian v. SCT for example), have light microscopes with a number of different optically diverse objectives from the same source whose optics are all designed to match a single set of eyepieces. Finally, and distinct from telescopes, microscopes have light condensers with optics matched to different types of objectives (phase, dark field etc.). Binocular heads for microscopes thus end up being part of the basic product. Binocular viewers for telescopes, however, come as a subsequent add-on and telescopes, especially the focusers, are typically not designed with their use in mind. Another difference is that to change magnification the routine approach with a telescope is to swap eyepieces, whereas with a microscope you change the objectives. Finally telescopes rely on incoming light which a binocular head will attenuate. With a microscope you adjust the light source intensity to suit. So overall telescope binocular viewers, tend to be a later optional add-on, third party produced and need to be adapted to diverse telescope optics and eyepiece configurations so the whole matching process is much more hit and miss.
Binoviewer Cost/Sourcing Considerations
Everyone operates on a budget. Sometimes it’s absolute (you don’t have the money), sometimes you’re just a scrooge, sometimes it’s wanting to avoid throwing good money after bad – a greater risk with mail order.
With the last two points upmost in mind I checked the catalogues at all Australian shops with a shop front as listed in Quasar Astronomy. Like Bintel, none offered binoviewers. On-line I identified several ‘trust me’ general shopping sites but these were useless. More promisingly 4 mail order specialist telescope suppliers - Australia telescopes, Astroshop, Ozscopes, and Telescopes-Astronomy did offer binoviewers. Unfortunately the variety and specification details were too limited to satisfy questions I had arising from reading the blogs and only one binoviewer model was generally available from each supplier. Local prices ranged from $400 to $700, a tad higher than for the same model offered in the US, but generally less than UK/EU sites. Overall, the webs sites reported current (2013) prices in the range of $180 to $1200 for basic binoviewers, and most importantly there were many more models available than in Australia along with various accessories. Other uncertainties/issues were the need for matching eyepieces and filters suited to each viewer, the pointlessness of buying good eyepieces but a poor quality viewer and vice versa, the likely need for good flat field eyepieces to ensure image merging, and the question of whether the final choice would work with any or all of my own telescopes (CPC 800 Cassegrain, Lightbridge 12” Dobsonian, Eon 72mm refractor). Scanning the available reviews and blog comments didn’t instantly clarify things.
I concluded: 1) my choice would be a shot in the dark to some degree; 2) on-line purchasing was inevitable; 3) minimum cost for viewers + eyepieces + filters would be $500 plus, equivalent to a complete basic Dobsonian telescope kit; 4) I should re-immerse myself in the information available and go for something reasonable but not necessarily top of the line; 5) with all this in mind make an informed binoviewer purchase, return to my telescope shop to physically try out a number of candidate eyepieces on their display telescopes, get informed tips and then trial the binoviewers on my own instruments.
The Wisdom of the Crowd
After screening out shotgun marketing, self-serving and information thin sites I identified a mix of useful articles and conversations. I’ve compiled the links to the most useful ones in the Appendix at the end of this review. Several have large amounts of valuable technical detail. The main points of interest to a newcomer, at least as I understand them as another novice, are summarised here.
The idea of seeing the stars in stereo is very seductive. And there is a degree of reality in the promise. However, don’t be fooled into thinking because others say ‘Wow’ uncritically. I’ve seen this in several of the blog threads (maybe they were commercial trolls) and echoed on some commercial sites without appropriate warnings to the effect “These binoviewers may not work with your eyes or your telescope using your preferred eyepieces or your favourite target”.
Issues of Concern
The rule as usual is “try before you buy” if you can. I couldn’t, but clearly club goers have the option of looking over someone’s shoulder and borrow viewers if possible. Those who have this option would need to have their own telescope(s) handy. Nevertheless the information below should at least aid discussions and identify what traps to look for and what questions to ask.
Telescope Back Focus (Most critical)
All telescopes are optimised to come to a focus somewhat beyond the point where light exits the tube allowing (Cassegrain, refractor) or not (Newtonian) for a star diagonal. This is the ‘back focus’ where the eyepieces are located. Descriptions of focus theory can be found at wikipedia . The trouble with binoviewers is they greatly increase the effective length of the telescope tube, often to the point where eyepieces can no longer reach focus using the existing focusing tube. Put another way, telescope tubes are currently sized/designed to reach focus with a single eyepiece and possibly a diagonal. But a binocular head throws this calibration out and depending on the telescope it may be fatal.
While all three main optical configurations can reportedly use binoviewers it appears that Cassegrain configurations have the least trouble because their long focal length leads to a flexible back focus distance, while Newtonian and refractor optics have more trouble. In practice the severity of this problem varies between telescopes and there are also ways around it. The main one is to insert a so called glass path compensator (also termed a ‘Corrector’ which is in effect also a Barlow) in front of the binoviewers. This is also reportedly designed to correct colour aberration. Alternative if you are having trouble reaching focus, one post suggested inserting a normal Barlow.
Inter-pupil (and eyepiece centre) distance and Eyepiece Selection
With binoculars and binoviewers the inter-pupil distance (distance between the two light paths of the split beam) needs to be variable between about 50 and 75 mm to suit different individuals. The eyepiece fields also need to be wide and have good overlap, in practice with about 40 – 50 degree field of view. They also need to be flatfield.
Eyepieces can’t be too chunky else you won’t be able to position them close enough. Once you have selected your binoviewers you need to check they can be positioned close enough together with the selected eyepieces to allow image merging. You can’t use 2“ eyepieces if only because no binoviewer holders take them – at least all I saw.
Typically eyepieces range in focal length from 3 mm up to 50 mm. For binoviewers though it appears the useful recommended range is in the region of 15 to 30 mm with a still more limited range being often recommended (16 – 25 mm). Note that resulting magnification will be higher than usual where a glass path compensator or Barlow is used. Matched zoom eyepieces apparently are usable.
Individuality of Stereovision
Not everyone can easily merge images when using binoculars. I usually don’t have a problem but others report they do. Part is physiological apparently but it may be optical quality in part too – when I’ve loaned friends my 63x9 Orion mini-giant conventional binoculars many remark they can finally see stereovision using binoculars. I find the mini-giants easier to use too than smaller models. The same issue could be expected to apply to binoviewers and there also seem to be people who can’t see stereo full stop.
A common concern with telescope binoviewers is loss of light intensity at the edge of the ocular fields due to suboptimal optics (see blogs for further comments).
Split optics and Reduced Light Intensity
At times / with cheaper binoviewers a noticeable difference reportedly arises between the amounts of light passing down each path. This is supposed to relate to the quality of binoviewer prism optics – a low quality prism gives a poor split – see blogs for further discussion.
A separate concern is that the same eyepiece model, but from different production batches, will have different transmission properties leading to the same effect. Another source is as mentioned the use of a Barlow /Compensator will inevitably reduce the light intensity per unit area.
A inherent limitation is the reduction by a factor of two in light reaching each individual pupil for the obvious reason that the incoming beam has been divided. However, it also appears that image construction by the brain compensates by a factor of 20 to 40%. This suggests in the absence of magnification you sacrifice about 0.5 orders of magnitude in telescope sensitivity set against reportedly 3-D viewing and improved image contrast.
While any drop in light intensity is clearly undesirable, and to be avoided if possible, it was unclear whether this drop is excessive for many observations given 1) for objects other than DSOs, contrast and relief are more important; 2) dark adaptation keeps increasing logarithmically for up to 30 minutes; 3) local seeing factors like streetlights and atmospheric conditions have bigger effects; and 4) we routinely accept loss of intensity through the use of filters to gain better images anyway.
Moon v. Planets v. DSOs v. Terrestrial
The viewing experience was reportedly different between target types reflecting their brightness. The moon comes into very high relief (Personally I’ve found the moon hard to stay focused on with single eyepieces because of the eye strain so the prospect of easier viewing was very attractive). The planets are also reportedly better (Though limited eyepiece flexibility had me worried that optimum magnification would be unavailable). DSO reports vary – bright nebulae are reportedly spectacular but the benefits with dim ones appear less.
Age of Review/Blog
Quality of optics seems to be improving rapidly all the time. So it’s unclear to what extent older blogs/posts are indicative of current optics quality. Certainly many of the binoviewer models reviewed/compared in the past have been superseded. There were various comments on good German v. dubious Chinese optics. But I take this with a grain of salt as silly as ‘Made in Japan’ whose meaning has transformed in my lifetime. Anyway with globalised manufacture it’s more about QA/QC of the final product.
Binoviewer weight and Telescope Balance
Telescopes tubes are generally sized to use/focus single objective/eyepieces. Binoviewers use means a big additional mass (0.5 to 1 kg) plus a second chunky eyepiece at the end of a lever putting strain on the fulcrum if not properly balanced.
A common concern raised was that not only will the telescope balance be thrown out but the holding screws on a normal diagonal may not be able to hold the extra weight – worst result is that the binoviewers and eyepieces fall out or tripods overbalance either breaking equipment or disturbing the binoviewer prism alignment or both after which things are never the same.
Exit pupil and observer age
The exit pupil story is still a bit Greek to me. But there was a report of some gain in this area (see blogs for informed discussion).
There has been some discussion about the effect of a person’s age and hence state of their eyes on viewing but whether the effect is good or bad was not resolved.
A 2” diagonal or exit tube
It appeared with Newtonian optics a 2” pre-binoviewer compensator may be preferable. It was unclear how much other telescopes might also benefit. Note this does not imply the use of 2” eyepieces.
One site identified 14 brands and 33 models. The consensus on the best seems to be Televue which are also the most expensive. No surprise. There are several comparisons of these with other competitors but they felt a bit like they were trying to compare an LX 200 with a 1960s Tasco reflector – not really fair or that useful beyond confirming ‘you get what you pay for’.
When I made my purchase I appreciated the above complex of issues even less. So I went largely on the principles that ‘you get what you pay for’, ‘a commonly discussed and compared brand apparently lacking fatal flaws is probably worth considering’, ‘top of the line equipment will not be cost effective unless all your other equipment is of comparable quality’, ‘a credible distributor selling a range of equipment from basic to the best has probably been selective and is much less likely to sell crap’, ‘a good manufacturer who is proud of their product and has other good optical products will provide details to help you through the minefield of choices’, ‘lots of suppliers and choices means being able to compare and get best value for money’.
While these ‘principles’ are not optical, they seemed the best criteria I had for purchasing a unit sight unseen. Another consideration was that I was visiting the USA for three weeks and this would allow both application of these principles and unit replacement if something basic appeared amiss upon receipt.
A ‘Mistake’ with the Base Model Celestron
Cutting to the chase I identified Highpoint Scientific in New Jersey as a likely good supplier as they had a short supply delay, 5 different well commented on binoviewer brands, models and accessories. There were other suppliers not too different in price but Highpoint were the cheapest and I have a soft spot for the Noo Joisie accent.
The most attractive model for a Scrooge was the bargain basement Celestron model. At $190 from a major Telescope manufacture it seemed like there wasn’t too much to lose. However, I got it into my head from one of the blogs, that you couldn’t adjust their inter-pupillary distance (In Fact You Can). Nevertheless this caused me to look at the next model up, the Baader Maxbrights.
In hindsight this was the right decision for the wrong reason. However, if my only telescope had been an SCT I think the Celestron basic unit could have been my choice as the blogs seemed reasonably complementary suggesting its optics are basically ok.
Selecting the Baader Maxbrights
The first plus with these was the base price of $270 appeared only marginally more than the Celestron even though they offered a range of accessories which might be important along with much technical supporting information indicating why they were. Also the Celestron appeared designed alone for with SCTs while the Maxbrights appeared suited to all telescope types at least on paper. So given my other telescopes I thought the Maxbright made more sense.
A limitation that emerged was that the base unit did not seem to include a nose piece (essential). Why puzzled me at first. Instead the nosepiece came with the $ 350 package as part of 6 different compensator+nosepiece combinations which I had to specify (Did I need one?). Competing products such as Denkmeier and Televue also had diverse options/packages with different terminology but for substantially higher cost and they looked pretty heavy. This was getting confusing.
More understanding emerged through finding a detailed users PDF manual for the Maxbrights via Alpine Astro (link below) which explained the back focus problem. It also explained other constraints of binoviewers, and how the different Maxbright options addressed them – and did so in plain enough English for an optics illiterate like me. Other makers probably have similar information but I didn’t go further as the price consideration and my visit duration in the USA dictated it was decision time. Another plus was that Maxbrights were reportedly smaller and lighter. As a result I ordered a ‘standard’ Maxbright package (bino head, 1.25 inch nose piece, 1.7X corrector/compensator).
The Highpoint ordering instructions explained that there were 6 different options (11, 12, 13, 21, 22, 23). What the hell were these? It turned out these were the 3 different compensator lens/Barlow strengths (1.2, 1.7, 2.6 X) and two nosepiece sizes (1.25 and 2 inch). The explanation was to be found from a close reading of the PDF instructions on the AlpineAstro web site but absent from the Highpoint site. A constraint was being in the US I couldn’t estimate my telescopes’ length and focus travel which are critical to making the right compensator choice. So I chose the most recommended combination and hoped for the best. The 1.7X compensator with 1.25 inch nosepiece was Option 12 I believe (Warning do not take my word for this!). If I needed other options in the future I could still use the same binocular head. Another feature of note was strong exhortation by Baader to consider their various diagonals and other accessories including eyepieces. I left those for another day as it was unclear how essential this other proprietary stuff was.
Receipt of Maxbrights
Having time in the US proved good because of billing hiccups. Once these were sorted the binoviewers arrived 2 days after order confirmation.
I couldn’t obviously test them properly but a quick check indicated no scratches or damage. The pack included a solid metal case similar in design to an eyepiece case but smaller. The feel of the binoviewers was also solid. The appearance was of a well machined product which was not about to fall into a dozen pieces or flake paint. The three main components - binoviewers with eyepiece securing screws (3 each eyepiece), the nose piece and the compensator – came in separate boxes. Assembly was consistent with this being a robust piece of kit. I packed everything into the metal case and put it into the hold baggage confident it would survive the return trip.
Eyepiece Selection and Shop Trial
A little the wiser I returned to Australia and trotted down to Bintel on a rotten rainy afternoon with the binoviewers and my boxes of existing eyepieces and filters to try a mix and match and purchase.
Sadly my preferences weren’t available - a (second) 15 mm wide relief Orion eyepiece was no longer stocked and no 32 mm Televue Plossls would be available for a fortnight. Too impatient to wait, bearing in mind the eyepiece focal length range recommended, the desirability of a single batch, the need for flatfields which didn’t bang into each other, and finally the convenience of having a dedicated eyepiece pair, I tried other eyepieces close to the 32 mm Plossl on telescopes close to mine in specs. We ended up selecting a pair of 27 mm Orion Edge-Ons on 3 telescopes.
The trial supported the web information. The refractor (short 80 mm Skywatcher I think) had trouble making focus when using a diagonal with or without the compensator though focus could be achieved after removing the diagonal. We had no success at all with the short Newtonian (a 6 inch Skywatcher or equivalent I think). Finally the 200 mm LX90 Cassegrain worked sufficiently well on a terrestrial rainy day target for me to take the plunge. I bought the Edge-ons and a second moon filter.
First Light and Other Trials
In the end the only real test is whether a piece of equipment works. Dot points below give the results of the tests I did:
Environment and Equipment
Eon 72 mm refractor (400 mm F 6/0) – first light
CPC 800 Cassegrain (2000 mm F/10)
Lightbridge 12” Dobsonian 1500 mm, F/5
Finally I repeated the test on the big telescope. What a disappointment! I had hoped that the large mirror would address the light reduction issue and make viewing DSOs with the Dobsonian a more comfortable affair, and the compensator + Barlow trick would get me over the line again if necessary. But the focus point was still far away with and without the Barlows. I simply couldn’t achieve focus with the Maxbrights. A strong Barlow might make focus achievable but this would reduce light intensity.
Comparing the refractor’s specification with the Dobsonian showed the likely reason. Basically the Newtonian focuser had only 3 to 4 cm total travel whereas the refractor had 7 cm. There simply wasn’t enough travel in the supplied focuser. Apparently even with any of the available compensators there is still an additional 31 to 44 mm of focal length required with the Maxbrights. By contrast, the entire focus available for the Lightbridge was only approximately 30 mm. So whether the available solutions would work with this telescope type is unclear. Baader instructions provide more detail and a possible solution of a special 2” compensator fitting. However, it’s notable also that AlpineAstro have a prominent warning specifically about back focus and Newtonians. For further information see Table 1 here. What is clear is that Newtonians need a strong Compensator/Barlow to go with an add on binoviewer and this would tend to dilute incoming light and make the Lightbridge images little better that the CPC 800 despite its larger mirror. That said Barlow’s up to 5X are commercially available.
I think the best strategy will be to watch/review the blogs to see how much success people have had in using binoviewers with fast Newtonians and see whether the Baader option will work on such telescopes. Alternatively the telescope and binoviewer manufacturers need to work together to come up with solutions tailored to Newtonians which do not require large Barlows. Baader seems to be trying but I’m no sufficiently convinced. Maybe Meade and Celestron and the other big Dob and binoviewer manufacturers need to develop binoviewers suited to their instruments.
Conclusions and Final Comments
If you are a serious astro-photographer primarily I’m not sure binoviewers will do much for you. But if you are the direct viewing type, who hasn’t the inclination to build or buy a stereo telescope, Binoviewers with Cassegrains make very good sense. With refractors and especially Newtonians care is needed to make sure they will work and strong compensators are compulsory.
The Maxbrights themselves though the second cheapest I identified proved to have optics able to take advantage of the CPC’s performance and did everything I hoped they would from reading the blogs and understanding their limitations. The catch is with these, and I suspect any binoviewer, you really need a tracking system and Cassegrain (or possibly Matsukov) optics to take full advantage of them. It’s the combination that made the moon and planets vastly interesting again.
For entry level observers on a limited budget with a cheap powerful Dobsonian, investing in better eyepieces first makes more sense and indeed binoviewers might not even work with these telescopes (though perhaps a strong Barlow might work). But if you have the cash and a Cassegrain (Matsukov or SCT) the marginal cost of $500 to $600 thereabouts may make sense. (Don’t forget you need to buy both a binoviewer and at least one good flat field eyepiece and ensure you are getting the corrector in the package).
I have tried to find some scientific journal articles on the improvements/benefits of binoviewers but to surprisingly little avail. There are old citations going back many decades - but they don’t benefit for modern neurophysiology and are usually directed at other concerns e.g. head up display functioning, interpretation of images. Up to date information on how stereo microscopes improve vision seems remarkably thin and perfunctory. The best I could deduce is that the process is a complex mix of physical light levels, neuron interaction and perception changes between the use of one and two eyes which aren’t just about stereoscopic vision. This may be covered in the old article in Sky and Telescope but I didn’t check. We are for the most part stereovision based creatures and the models of landscapes and star-scapes we assemble in our brains probably reflect this. We can look at expanses for hours when using two eyes but our wiring but monocular viewing needs to be learnt. In a quest for better telescope views we usually think of increasing magnification + higher quality eyepieces + bigger telescopes – The technical fix as it were. The reasons I suggest have been the optical challenges, the need for a long focal length best supplied by an SCT, the past cost and availability of good optics and the fact that CCD and time elapse photography have greatly pushed the viewing boundaries in a different direction. Now while I don’t decry these improvements they don’t address the fact we are using only half our visual system. Binoviewers do this.
I’m still pondering whether the cheaper Celestrons might also make sense. These are clearly designed to support their SCTs and if that is all you have then maybe. They don’t appear to be optically flexible as supplied but their use with different Barlows seems to make sense. I’m also interested to know when more expensive binoviewers would make sense. For the moment I’m thinking I would buy them if I ever went to the next level of equipment like a giant 14” Cassegrain. Maybe in ten years when I have the muscles of Arnie.
Appendix – Links to Informative Reviews, Discussions and Other resources
This appendix provides links to web sites I found especially useful. Cloudy Nights was particularly useful. Reflecting my paper chase and review subject there is some a bias toward Baader and Maxbright details but most of the issues and information can also be read generically.
Detailed Apparently Unbiased Overview Appraisals
Responses to requests for advice