Oberwerk 80mm 45° Binocular Telescope
By Silvio Jaconelli
As stated by Kevin Busarow of bigbinoculars.com, this ‘Obie’ is a serious competitor to the mid-range Mayauchi models. I have already owned bino products from Miyauchi, Takahashi and Denkmeier and I am now firmly in the two-eyed camp, finding that this provides me with a much more comfortable viewing experience in addition to squeezing more detail from a given magnification.
Let me state at this point that working with Kevin at bigbinoculars.com was an exceptionally pleasant experience; for me, he has set the standard for customer service.
This new binocular telescope (BT) has 45 degree angled eyepiece holders which accept regular off-the-shelf 1 ¼” eyepieces. Bigbinoculars.com specifies a 520mm focal length for a focal ratio of 6.5, high for binoculars. This was a plus factor for me as my viewing targets from my light polluted Phoenix area backyard are the Moon, sun, planets and double stars.
The weight of the BT is listed at 16 pounds, for a total rig weight of around 25 pounds when a Bogen 3076 tripod and Blaho Stedi-vu mount are included. For $300 extra, a custom fork mount/wooden tripod is available, but I elected to forego this option since I already had a mount/tripod combo from my Takahashi 22x60 days, and since the custom tripod was fixed height. The Bogen tripod has a variable height ranging from 4 feet to 8 feet. I think that I am losing some stability here, but the convenience of the variable height outweighs this for me. This combination of fork mount and 45 degree eyepiece holders allows the BT to easily view at zenith, something that was next to impossible for me to do with the Takahashi 22x60 straight through binoculars.
The 80mm BT is a doublet while the Obie 100mm is a triplet and much heavier at around 26 pounds, with a total rig weight of over 40 pounds. I have read that the combination of weight and size of the 100mm BT makes it not a portable rig. However, the 80mm BT can be moved around my back yard with ease, and I keep it fully set up in my living room so that no assembly/disassembly is required. Set up time is a few seconds. I use an $8 Daisy red dot finder to point the BT, and for really faint targets I look through the Daisy finder with handheld binoculars for a right side up 7x image. I paid $900 for the 80mm; the 100mm sells for approximately $1,500, I believe, without mount/tripod.
I already have a selection of eyepiece pairs from my binoviewer addiction. These specs on these as they apply to the BT are:
Orion 32mm Plossls yielding 16x with a 3.3 degree fov and a 5.0mm exit pupil.
Obie 26mm Erfles yielding 20x with a 3.1 degree fov and a 4.0mm exit pupil.
Denk 14mm on back order yielding 37x with a 1.8 degree fov and a 2.2mm exit pupil.
UO 9mm HD Orthos yielding 58x with a 0.7 degree fov and a 1.4mm exit pupil.
Nagler 7mm Type 1 yielding 75x with a 1.1 degree fov and a 1.1mm exit pupil.
I also have a pair of UO 18mm HD Orthos but I need an additional 2mm of in travel to get them to focus!
The eyepieces are friction fit, with a pair of rubber ‘o’ rings embedded inside each eyepiece holder providing the friction.
The only eyepiece pair that did not deliver sharp images was the 7mm Naglers and I interpret this to mean that the BT’s top magnification is in the 70x to 80x range. I guess that I need to try out a pair of later model higher quality eyepieces to see if the image quality improves. The only real downside with this BT that I have encountered is that sometimes it is not easy changing eyepieces due to the overly snug fit – it sometimes takes some muscle to extract eyepieces, and this results in the image moving out of the eyepiece field. One solution might be to use a pair of TV 8-24 click stop zooms giving a magnification range of 22x to 67x – hmmm, that’ll set me back $450, and I’m not sure if they will come to focus…… For right now, I’m using just three eyepiece pairs – 26mm Erfles for wide FOVs, the 7mm Naglers for high power, and the 9mm Orthos for when the Naglers are limited by the atmospheric seeing.
Roy Bishop of the Royal Astronomical Society of Canada extols a concept called Visibility Factor which allows comparisons of what can be seen in different binoculars. Simply put, the detail that can be seen is a function of two variables – magnification and aperture. The factor for a particular binocular is computed by simply multiplying magnification by aperture, assuming that the magnification is NOT pushed to excessive extremes. So a 7x50 instrument will have a visibility factor of 350, while a 15x60 instrument will have a visibility factor of 900, almost three times as much. Looking at large binoculars, a 20x100 instrument will have a visibility factor of 2000, and a 25x125 instrument will be at 3125. Pushing the Obie BT to my own magnification ceiling of 75x, yields a visibility factor of 6000 (75x80), almost twice that of a 25x125 binocular. My experience with the Obie BT’s bears out this concept – see the ‘PERFORMANCE’ section below.
I found that the only time that chromatic aberration was very obvious was at 75x on bright objects during the day; there was copious blue fringing around white walls in sunlight, but this fringing was much less at lower powers. And at night, any color fringing was barely noticeable unless I was looking for it. For me personally, the BT has acceptable performance on chromatic aberration. Off axis, I get the usual bending of straight linear objects – expected and nothing unusual.
At lower magnifications, the images were excellent. As usual, the Moon was remarkable. Open clusters and brighter nebulae (Pleiades, Beehive, Double Cluster, M35, Orion Nebula) were very nicely framed against the background sky – Saturn and the Beehive at 2 degrees apart fit in the same low power field of view.
Stars dimmer than 4rd magnitude were tight, while some flaring in brighter stars was evident; this flaring might be due to my eyes rather than the BT – I’m not sure. This flaring interfered with my ability to split double stars with bright primaries and faint secondaries such as Rigel and Theta Aurigae.
It was at the higher powers that the BT really performed. Much of the observing at 75x really was in the province of telescopes rather than binoculars. Then fold in the apparent increase in image scale by using two eyes rather than one eye, and indeed the images were telescope-like. For example:
Saturn – at 75x there was a great deal of black space between the rings and the globe – the nature of this object was totally apparent. In fact, the views at 58x were even better – much sharper and more pleasing with no loss of any detail compared at 75x. However, no surface detail was seen at either magnification, nor was the Cassini division ever resolved. I was using ‘deep sky’ old vintage Naglers at 75x and using ‘planetary’ orthos at 58x – I really need high power ‘planetary’ eyepieces to see if they better the Nagler images. More cash outlays.……!!!!!
Mars was a small orange globe. I thought that I could detect just a trace of a vertically oriented marking in the image but I was not sure what it was. I then checked my Mars chart and guess what – Syrtis Major was on the meridian at that very time. Syrtis Major through binoculars – wow!! Now I need red filters. More cash outlays……!!!
Sun – I still need to make up some solar filters to allow me to view the sun. The sun is normally like the Moon – spectacular images at 40x to 50x, so I really need those filters. More cash outlays……!!!
The Moon at 75x showed Rupes Recta (the Straight Wall) so very obviously. And Vallis Schroteri was easily visible although the views were not so crisp. And Catena Davy was observed as a faint fuzzy line running across the Moon’s floor. The Moon images were so bright that I need Moon filters. More cash outlays……!!!
Double star performance was excellent. I was just able to split Rigel (mags 0.1, 6.8; sep 9.5”) on one evening although not on another. Flaring and the big magnitude difference in the components is a real challenge. But Iota Orionis was easily split (mags 2.8, 6.9; sep 11.3”), as was the three components of Sigma Orionis (mags 4, 7, 7; sep 13”, 42”); the 10th magnitude companion (sep 11”) was blotted out by the very bright primary. The Beta Monocerotis triple, on the other hand, was a very easy split (mags 4.7, 5.2, 6.1; sep 7.2”, 9.9”). The Trapezium was also a very easy split. Theta Aurigae was like Rigel – the flaring and the big magnitude difference prevented splitting.
The real surprises were the double stars with tight separations that the BT was able to resolve, targets that I thought were the exclusive domain of telescopes. These included:
65 Piscium – Mags 6.3, 6.3; sep 4.6”
Struve 750 – Mags 6.5, 8.5; sep 4.2”
1 Arietis – Mags 6.2, 7.4; sep 2.9”. This one was really tough, seeing elongation only. Through the eyepieces, I guessed the position angle to be 180 degrees; then I checked my star charts – the position angle was given as 166. Eureka – I was able to break the 3” floor!!!! Well, humour me, everybody – allow me count ‘elongation’ as ‘resolution’!!!
Oh! before I forget, Castor was easy – Mags 1.9, 2.9; sep 3.9”.
I’m delighted with the overall package. The best images I’ve ever seen through binoculars were the Takahashi 22x60, but these were very expensive, straight through, low power, single magnification units; the Obie BT is much less expensive, has angled eyepieces, and variable magnifications – the image trade off is definitely worth it to me personally. To summarize:
Good image quality
Easy zenith viewing.
Infinite magnification options.
Excellent customer service from bigbinoculars.com.
Changing eyepieces can be a chore.
Now I need to find the money to pay for all the extras that I want!