Description
The all new Theia90 1/10th Wave Telescope Star Diagonal is now available. Load up your filters in advance into our quick change filter holders and you can rapidly swap from one filter to another. Using high power magnets to hold the filters in place you can meridian flip the telescope and not drop the filters. When you want to change you simply pull the filter out and replace it.
The diagonal uses a 46mm minor axis mirror with 1/10th wave finish and each unit comes with an individual Zygo report so you can be sure of its quality.
Using the 4 screws on the back the position of the mirror can be altered to help collimate your telescope. The unit comes in a sturdy mini cerberus case which is just a tough as its larger brother.
The 2″ nose of the Theia90 can be unscrewed so you can attached the body directly to any M48 x 0.75 male thread focuser or exit port.
Supplied with 3 filter holders. Additional holders can be purchased here:
https://www.npae.net/product/pack-of-three-2-inch-filter-holders/
The Theia 90 Photo Gallery
Astronomy Now Review:
The diagonals mirror is of excellent quality, and observational comparison with one or two of my own diagonals gave me no cause to doubt that the 46mm (minor axis) mirror is as stated, one-tenth wave with 99 per cent reflectance.
The beauty of this system is that filters can be placed in this primary optical position, doing their task unmoved for any eyepiece or camera changes ‘downwind’.
True to its makers’ name, this diagonal is a precisely made piece of astronomical engineering, and I have no hesitation in recommending it.
We also have the filter changing system available as a separate solution, check it out here:
juliancaroline –
The item is very well made and feels substantial. It weighs 545 grams so will not add too much additional load to your mount. The individual filter holders fit well and are held securely by small magnets into the main diagonal body. Each filter holder has a clean thread for screw mounting individual 2″ filters in place. There is also a screw thread to mount an additional 2″ filter direct to the main body of the diagonal.
The eyepiece/camera holder has two thumb screws tightening a compression ring to ensure secure mounting of any eyepiece or camera.
The unit comes in a tough, water and dust proof box similar to a Pelican case together with an individual wavefront Zygo analysis report specific to the diagonal.
Mark Jennings –
First I would like to say that this Diagonal is very beautiful and impressive looking.
I was not going to compare it to my Zeiss Prism Diagonal ( which I have been using ever since I aquired it),
However, the Theia 90 Diagonal is Collimatable, so I put a high power eyepiece in and checked my collimation.. (just a tiny bit off), I am a big believer in Good Collimation (it makes such a difference). So I Collimated with a Star Test, and the view improved significantly, the Stars were Textbook perfect and SNAP into focus nicely now… (Something that my Zeiss could not do).So I looked at the 1st Quarter Moon so I could see how the interchangeable filter inserts worked and this is a Fantastic feature.You can change color filters effortlessly. And also you don’t have to rethread your filters just to change eyepieces either.This Diagonal is very convenient, no more fussing around with filters in the dark.
I really like this Diagonal, and recommend it highly. Nice Job nPAE, now I am wanting to see what other great products that your company is producing!
Jack –
I’ll say right at the top, I didn’t give the Theia90 five stars because I couldn’t actually use in on my scopes. There are details below, but it didn’t allow for enough in-focus travel.
I saw the thread/ notice posted on Cloudy Nights by nPAE asking for people willing to try out their Theia90 diagonal and write a review of it. I contacted nPAE and began exchanging e-mails with them. Soon enough, a small package was on its way from England.
The Theia90 arrived in the proverbial “plain brown wrapper”. Inside the box is a small Cerberus case, similar to a Pelican case. To me, the Cerberus case is overkill, but it is a nice case and if I ever start travelling to star parties (perhaps in retirement?), I’ll appreciate such a durable case to protect my astronomy gear. After all, I did save the packing crate my last telescope was shipped in.
After I was finished the unboxing, I gave the Theia90 a closer look. Machining is quite nice. All surfaces are smooth and appear to even be bead blasted creating a satin finish. The nose piece fit in the focuser of my refractor and my friend’s C11 with minimal slop (zero slop would make installation pretty fussy). I used my caliper to measure the nose piece: 1.97” – 1.99” outside diameter, depending on where I measured. It is internally threaded, female M48, for filters (so the Theia90 can hold two filters simultaneously). It is not internally threaded (other than for holding filters), or machined with internal baffles, for stray light blocking.
The nose piece does have an undercut, so undercut-haters beware. It threads into the mirror housing, so it can be removed. Maybe nPAE will offer a smooth nose piece? One other variant for nPAE to consider: a nose piece compatible with the common 2” SCT thread.
The eye piece holder is anodized a contrasting color, my sample is red. It does not appear to be bead blasted; its finish is glossy. Two set screws, oriented orthogonally, push on a brass compression ring to hold your eye pieces. The set screws have big, knurled knobs which make grabbing them easy. I doubt I’ll ever know if the knobs are big enough for ski gloves (living on the Third Coast). With the popularity of collet-type holders, I wonder if nPAE will offer that in the future? The eye piece holder measured 1.99” inside diameter (consistently), but even with that tight tolerance for nominal 2” eye piece barrels, neither my son nor I had more than occasional hassle inserting or removing eye pieces.
Integral with the mirror housing is a single filter holder. The holders are threaded for holding the filters, and a pair of small magnets hold-the-holder in the diagonal’s body.
The back plate of the mirror housing is secured with screws, which are also used for collimation. I didn’t adjust the collimation of my sample. Keeping my scopes collimated is enough, so I trusted nPAE to send me a properly adjusted unit. The screws are hex drive and appear to be 1.5mm.
The Theia90 is a large diagonal, and it’s heavy. When I installed it in the focuser of a friend’s C11, you can see how far forward I had to position the scope in my mount’s saddle. Of course, this isn’t completely due to the Theia90, the focuser is also heavy, but you understand my point. The Theia90 is also longer than a typical 2” diagonal due to the integral filter holder. If you use a CPC or LX-200 type mount, there might be a clearance problem when pointing near zenith.
Under the stars, the Theia90 performed well. It was secure in the focuser and held my eye pieces solidly.
The bad news: I had trouble with the first two scopes I tried the Theia90 with. The first was my 6” refractor, which has a 2.7” Astro Physics rack and pinion focuser. That focuser has approximately 5” of travel (I am guessing, I’ve never measured it). Unfortunately, with the Theia90 only my 40mm eye pieces would come to focus. There wasn’t enough in-focus for other eye pieces I had on hand. I expected the same trouble with my classical Cassegrain, which is fitted with a Feather Touch rack and pinion focuser and a 1.5” draw tube. Frustration again. For my next attempt I borrowed a Meade 10” SCT (moving primary mirror, you know). With the stock visual back, I needed an SCT adapter to install the Theia90. Thwarted again. Finally, I borrowed that friend’s C11 with a Crayford focuser installed. Success. So the impressions you’ll read about below are from my observing with that C11.
On a nearly full moon weekend in July, my son and I made a trip to our club’s dark sky site (green zone). Since the moon would be rising between eleven and midnight, and astronomical twilight wouldn’t be over until half-past nine or so, we planned to spend time looking at Jupiter and Saturn. After sunset, but before it was dark, Jupiter looked amazing. There was plenty of detail to be seen in the belts and zones. The Great Red Spot, a favorite of my son’s, was hiding on the other side of the planet, but there was a transit in progress. So we watched the moon’s shadow (we think it was Io, but didn’t verify it with any astronomical websites). Shadow transits are one of my favorite solar system events. I love the razor sharp edges of the shadow and watching, in real time, the movement of celestial objects 400 million miles away.
Saturn, a bit later in the evening, unfortunately proved disappointing. Some clouds were moving in, and I’m sure the high elevation winds they were riding were playing havoc with the seeing. It was something that even a nice piece of kit like the Theia90 couldn’t overcome. I think I have an e-mail from Dave stating that nPAE is working with a European optical shop to introduce a seeing filter that will finally reduce the blurring effects of unsteady air. Even with the poor seeing we were at least able to see the Cassini Division and, during those fleeting seconds of good seeing, the variations in brightness between the A, B and C rings.
Views with the Theia90 were never less than bright. The diagonal I have on hand for comparison is a classic Lumicon. The two gave identical views.
Using the filter holder: this is what I was most curious about. From a convenience stand point it was really nice to add my UHC filter, or remove it, in ten seconds. Simply take one filter holder out and slide another in. The filter holders fit inside the diagonal body snugly, but slip in and out with little effort. I was able to test the holder with two filters: my Lumicon UHC and a Tele Vue Nebustar. My UHC fit perfectly. The Nebustar didn’t like the female threads of the Theia90 holder, but I was able to get one or one-and-a-bit thread engaged to be able to use the filter. Since the threads were a bit locked, removing the Nebustar filter was a bit tricky.
I don’t own binoviewers, but I wouldn’t expect any trouble using the Theia90 with binoviewers and any scope with a moveable primary or secondary mirror. You may find you have to shorten your refractor OTA even more to accommodate the Theia90 and your binoviewer, though.
I enjoyed my time with the Theia90 and am grateful to nPAE for a chance to use it, but it is on to the next person in line. I hope he enjoys it as well.
JM (verified owner) –
Todos los aficionados sabemos lo engorroso que resulta la inserción de un filtro en el ocular, y no siempre es posible montar una rueda de filtros, especialmente en las monturas de horquilla.
Basta una sóla sesión astronómica para apreciar la facilidad y comodidad que representa la inserción o el cambio de filtros con este magnífico cenital de diseño impecable. Theia90 rápidamente se convierte en un accesorio imprescindible.
Every hobbyist knows how cumbersome it is to insert a filter into the eyepiece, and it is not always possible to mount a filter wheel, especially on fork mounts.
A single astronomical session is enough to appreciate the ease and comfort represented by the insertion or the change of filters with this magnificent zenith of impeccable design. Theia90 quickly becomes a must-have accessory.