Comparing the Televue "Binovue"
to the BW Optik (Lumicon) Binoviewer
I recently had the opportunity to compare directly the BW Optik binoviewer to the Televue Binovue. They look remarkably similar, and have some similarities, indeed, but they do hold important differences.

Here are the advantages of the BW Optik unit first, then the advantages of the Televue.

1. The BW Optik/Lumicon unit was better collimated so that I was able to use higher power eyepieces more readily without having difficulty merging images. To be fair, the Televue unit is older, and may have fallen out of collimation. Also.. this was only a problem with 5mm eyepieces.

2. The BW Optik/Lumicon unit had a bit less in-focus travel needed, only around 4.7" even, compared to almost exactly 5" on the Televue.

3. The barrel on the BW Optik/Lumicon unit is much better, it is contoured so that it will not readily fall out of a diagonal.

4. The light throughput and on-axis performance were as good, if not slightly better than the Televue.

5. The illumination on each side of the unit was almost completely even, even better than the Televue unit.

6. The price is at least $300.00 less for the BW Optik binoviewer, but the price is actually fairly close if you purchase an additional 1.7X "magnifier" lens to help bring the unit to focus in many scopes. 

DISADVANTAGES OF THE BW Optik, ADVANTAGES of the TELEVUE BINOVIEWER:

1. There was some slight focus variation in the two different sides of the binoviewer in the BW Optik, especially on the 3rd unit I tried.

2. There is almost no "vignetting" on the Televue Binovue, like there is on the BW Optik when using low power eyepieces such as : a 30mm Ultima, or 32mm Plossl. It is slight on the BW Optik, but the vignetting is definitely there. Anything from a regular 26mm plossl on down would be fine, but the Televue holds no such restriction. The reason is that the TV unit has a clear aperture of around 26mm compared to 22mm for the BW Optik.

3. The Televue unit has readily available and numerous barlow options so that you can use it PARFOCAL in ANY scope. This is an advantage. From my understanding, The BW Optik unit can be fitted with a 1.7x correcting lens, to do the same sort of thing (available from Lumicon) but it still requires some 2 1/2" of in-travel. This would not succeed to focus in one or two of my scopes.

Also.. I  am not sure what this involves... or whether or not this will bring one to true "parfocal" use, but Marcus Ludes indicates he can retrofit this 1.7x correcting lens in such a way as to increase the magnification ( I assume between 2 and 3X ) and bring the unit to true parfocal use. (useable in any scope)

There is also a 1.25X corrector available that can fit on the BW Optik, but even more focus travel is needed to use that one.

(Meanwhile, using a regular barlow ahead of either unit will produce roughly 4X magnification... too much unless you are strictly planetary viewing. (see my binoviewer article in detail for more explanation of this effect.))

The Televue unit on the other hand is now sold with their 2X magnifier (low power barlow, I coined the term 'magnifier', and it "took"!) that can be screwed on to offer true 2X magnification, and parfocal use for ANY scope (no need to cut your tube or jump through hoops to reach focus, works perfectly). The previously offered barlow on the Televue binoviewer normally magnifies 3.8X, and can still be screwed on directly to the BINOVUE, if you buy it seperately, but be careful not to scratch your 2" star diagonal if it is the "threaded" style, which is slightly longer.

I also happened to try to concoct a unit out of the Televue 2x magnifier that would work with the BW Optik. Using the top of a "normal" 2x barlow from televue, and screwing on the new 2x magnifier cell, I was able to use it. However, it becomes a 2.1X barlow, and requires 3/4" of in-travel that way, not quite sufficient for 2 of my scopes (1 refractor, 1 newtonian)

A really odd thing about the new televue 2x magnifier.. it seems to work as a straight 2x barlow as well, when combined as outlined above, with the top of a normal TV 2x barlow (did I confuse you yet? ) Normally, one would expect the magnification to come way down when using a barlow on a regular eyepiece, as compared to a binoviewer, due to the shorter light path between the eyepiece and the barlow. This is evidence that this is not really a standard barlow but some other kind of magnifying device.

Bottom line on focus/magnification issues is that you are likely better off with the Televue unit if you aren't sure you can reach focus in your particular scope. However, with research and ingenuity, you may be able to get the BW Optik unit to focus almost at the right location, with reasonable magnification. The only problem I see with this, is that even if you succeed in using the BW Optik in this manner, the vignetting using 30mm eps or above is objectionable enough, that you still have a limited true field of view for deep sky compared to the Televue unit when trying to "milk out" as much field of view as possible out of your scope and binoviewer.

4. The Televue Binovue when sold with the Televue Bizarro (Televue 85mm shortened) telescope comes with a special correcting lens. I have tried this lens out, and on low power fields, it is absolutely outstanding, improving on edge performance (and apparently color correction) when you are using the binoviewer w/o any barlows. The BW Optik does NOT work well with this extra correcting lens. It doesn't fit right, and the view was not improved. I do not know if Televue sells this unit separately, or just with their Bizarro.