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Detailed test: Siebert 40mm VP Echelon

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Detailed test: Siebert 40mm VP Echelon  2” binoviewer

by Peter Vercauteren


After decades of observing with one eye only, I got fed up with having to close one eye all of the time. It’s tiring and therefore makes you lose those faint little details which you can only perceive when you’re completely relaxed behind the eyepiece. So I started browsing the market for a decent binoviewer without having to make any compromise. I’m a faint-fuzzies addict and the thought of having to lose quite some light was unacceptable to me. A “standard” 23mm binoviewer was therefore out of the question. The Denkmeier II or Baader Mark V were tempting, but still not good enough because it’s not just a question of light, but also of magnification. Being limited to 1,25” eyepieces would make low-mag widefield observation impossible. So in the end I turned to the only single one producer of 2” binoviewers: Mr. Harry Siebert.

Harry offers two types of 2” binoviewers: the big daddy 45mm Elite series and the 40mm VP Echelon with 2” eyepiece holders. As for the first the waiting list currently lies around 1,5 to even 2 years, I settled for the Echelon, which was ready and shipped within only 6 weeks!

General Impressions

I’ve been using this binoviewer for almost three years now, so I can truthfully say that I know it inside out, with all of its strengths and weaknesses. In any case, when the package arrived and I opened the grey box for the first time, I was seriously impressed. It’s big. Really big.



Whereas an ordinary 1,25” binoviewer would have a light travel distance of let’s say 12cm, this becomes about 23cm with the Echelon. Nevertheless its weight is very well contained and the binoviewer plus multimag OCA and a couple of Siebert Observatory eyepieces only weighs 1.365g! Not bad…


However, there were a couple of things I noticed at first sight which tempered my enthusiasm a lot. First of all, the VP Echelon doesn’t come with self-centering eyepiece holders and diopter adjusters. These features are available (as an option!) on the Elite but unfortunately not on the Echelon. Obviously this makes inserting an eyepiece a precarious business, not to mention the case where you want to use 1,25” eyepieces and also have to take the errors of the step-down adapters into account. The only solution is to revert to adjustment rings which you have to put around the barrels of your eyepieces. Fortunately this isn’t necessary with my 36mm Siebert Obervatories and 24mm Explore Scientifics because collimation and eyepiece distance is fairly equal between left and right. However, once you go below 20mm this does become an issue. Hmmm… Uncle Harry could’ve done better.

Then I saw that the binoviewer’s not really a custom thing but that its prisms are in fact… ordinary 1,25” star diagonals. There is the choice between mirrors and prisms. I ordered mirrors but received prisms and since I didn’t feel like going through all the customs hassle again I left it at that. The use of “ordinary” diagonals doesn’t necessarily have to be a bad thing, but as they’re 1,25” it does limit the binoviewers aperture somewhat. The front (beam-splitter) aperture may be the stated 40mm, the rear end I measured to be only 33mm. It’s quite a bit less, but still a lot more than the 27mm rear aperture of the Baader Mark V, the self-declared best deep-sky bino on the market. These 33mm are more than sufficient to fully illuminate, let’s say, a couple of 22mm Naglers. But the 36mm Siebert Observatories I got with the binos are vignetted somewhat and clearly don’t show the declared 70° FOV when used in bino-mode.

But the biggest disappointment was the multimag OCA unit. I expected that Harry’d deliver a 2” OCA for his 2” binoviewers, but this is not the case. The OCA’s nozzle is exactly the same as for his 1,25” units and therefore light loss is inevitable, especially with faster scopes such as my 18” f/4,45 Dob. After a phonecall, Harry immediately sent me an OCA with a 2” entry lens, but he warned me that it would not give such a sharp image as the 1,25” unit. The problem seems to be that it is very difficult to make a decent negative lens and whereas the same lens (manufactured by Edmund Scientific) will render superb images for the 1,25” Denk binoviewer, the much larger aperture of the 2” Siebert will reveal the errors of the OCA optics. And this is exactly what I saw at the eyepiece: a slightly brighter image but the stars were less pinpoint.

All in all the VP Echelon’s well made, sturdy and it looks quite impressive. But it didn’t give me the “I could jump over the moon” emotions which we astronomy lovers usually experience when we receive new toys.

Under the stars

So… out with the telescope and let’s see if my initial fears are exaggerated or not.

When you insert the mighty Echelon in the focuser, all people around you will stare in wonder. This is no ordinary binoviewer… this is stuff for professionals! Expect oohs and aahs all round! Be sure to have the balance of your scope well thought out though because this baby will cause more trouble than a 31mm Nagler with a Paracorr, especially with a couple of 24mm ES’s which will push the total weight to about 2,5kg. Therefore be sure that you have a decent-quality focuser because otherwise you’ll be in trouble. The Echelon however manages these heavier eyepieces wonderfully and I experienced no problems in that regard. What is a problem, on the other hand, is that the 24mm ES’s are so wide that not all people succeed at looking into both at the same time, even when the eyepieces are touching. With a couple of 22m Nagler’s however, no-one should have any problems.

And here I touch another precarious point: this binoviewer is not really suitable for public nights. The reason is that the eyepiece lenses are so enormous that it’s not evident to find the perfect observation position. It takes a bit of getting used to and in the beginning I noticed many times that the view wasn’t as bright as I had hoped simply because I was looking into only one eyepiece at a time. But once that perfect position found… open the heavens! I can assure you, I’ve looked into a lot of Ultra Wide and Extremely Wide eyepieces, but nothing in the world can beat the full immersion you get when looking into two 82° eyepieces in this binoviewer. You can’t see ANY field stop anymore. It’s like you’re standing in front of a vast plate of glass and wherever you look there are stars. In fact, it is impossible to see the field stop in such eyepieces because of the position of both eyes. Sometimes I closed one eye and pressed the other closer to the eyepiece and then I could see it. But once you return to viewing with both eyes you have to let go of that extreme edge of the FOV, but in turn you get the feeling that you’re commanding the Starship Enterprise. Stars are nicely sharp, perhaps slightly less so than without all of the glass of the binoviewer, but the view surely makes up for that.

So much for the good news. Now for the bad. Changing mags with the Siebert binoviewers is a pain if you’re doing it with the multimag OCA. You first have to pull out the whole binoviewer-eyepiece-OCA combination (making your Dob fly upwards if you’re pointing below 60° above the horizon because you’ll be out of balance all of a sudden), then you have to extract the front tube of the OCA from its holder, unscrew the entry lens, screw on another, insert the tube in the OCA again and then insert the whole caboodle into the focuser. Siebert does offer a Power Mag Wheel offering the same commodity as the Denk Power Switches. But this comes at a fairly high price and… isn’t available on the Echelon.

My fears were confirmed and the view was still dimmer than with single-eyepiece viewing. It is true that the binoviewer creates an additional magnification effect, but this doesn’t explain at all why I saw a lot less of the Veil with the binos than without. If you screw a filter on the nosepiece the vignetting becomes even worse. Sure, the difference with a “standard” binoviewer is simply immense, but to me it was far from satisfactory. I wanted to see just as much with both eyes and this didn’t happen. Therefore, if you decide to buy this baby and you’ve got a fast scope, you should seriously consider what I did: to cut a piece of my truss poles so I could observe without the use of a corrector. Suddenly things became a whole lot different. Now, I dare say that the difference with one-eyed viewing has become minimal, if not inexistent.

The downside, however, is that you’ll have problems reaching high mags. I already explained about the lack of self-centering eyepiece holders and the long distance the light has to travel through these binos. This means that if you intend to use high-mag eyepieces, the collimation and other errors of the binos are also magnified. Due to its long light travel distance the Echelon is a lot more sensitive to this than other binos and precision adjustments to the eyepiece’s position in the holders are absolutely necessary. Oh, did I already explain that the Siebert eyepiece holders only have one screw to lock the eyepieces? Yes… you see what I mean. Eventually it takes a lot of fiddling with adapter rings which may have to be fixed slightly slant, depending on the errors of the binos, and putting markings on them to indicate how exactly you have to place the eyepieces in the holders. But once all the rings are in place and the markings are correct, changing mags by changing eyepieces goes swiftly and without any problems. Phew! For the moment I tried up to a couple of 9,9mm Starsplitters and this was still ok. However I’m not sure if, let’s say, a couple of 5mm would still be usable without making you dizzy due to collimation errors.  

So do all of these problems make the VP Echelon a waste of money? To my opinion, certainly not! Apart from the Siebert Elite there doesn’t exist a single binoviewer in the world which leaves you with your mouth wide open and drooling the way the Echelon does. Even faint nebula filaments leap out at you as if you were observing in monocular mode, but with a spacewalk in 3D feeling that is yet unmatched. And also without being limited to higher mags such as the “standard” binos. There are OCAs on the market that offer no additional magnification, but the question is… do they come to focus in a Dob with limited focuser travel? And in the end, only the Echelon is capable of hosting for example a couple of 22mm Naglers and this without any vignetting.


The Siebert VP Echelon is definitely not a binoviewer for beginners, nor is it a good idea to use it on public nights. You must have a certain experience in order to find the right position in front of the (gigantic) eyepiece lenses and for being able to adjust the binoviewer to your own requirements. Diopter, eyepiece positioning and image merging all need a bit of work and the complete lack of aids such as self-centering eyepiece holders and diopter adjusters make this a precarious business. I would also recommend to use this binoviewer without OCA simply because there is no OCA on the market which would be a perfect match for the binoviewer’s 40mm of front aperture. So with an OCA be assured of some vignetting and significant light loss.

This binoviewer on the other hand is to my experience the only one which offers you uncompromised deep-sky viewing. So the question you have to ask yourself is, do I go for a Denk of Baader Mark V because of their ease of use and lack of diopter/collimation issues but accept a lower performance on the faint fuzzies? Or do I accept the hassle of the Siebert because I don’t want to give in a single foton on difficult deep-sky work? Without of course forgetting that the Siebert is the only one capable of handling large 2” eyepieces and it does this well. The only limit there is the distance between your eyes so before you buy a couple of large ultrawides, you’d better check whether you can look in both of them at the same time. In any case, the Siebert VP Echelon opens you a window on the heavens, much more so than any eyepiece or binoviewer can do. And this at the very reasonable price of $999 (OCA and eyepieces excluded), which is even a lot cheaper than the Baader.


- Unmatched aperture and light gathering power

- No more compromises on faint deep-sky work

- Suitable for 2” eyepieces with no vignetting at all up to a 33mm field stop

- Well built and excellent quality (apart from the ordinary diagonal prisms)


- No diopter adjustment, nor self-centering eyepiece holders

- Only one screw to lock the eyepieces

- High-mag eyepieces may be a problem due to the issues above

- Any OCA will cause either light loss or image degrading

- Not suitable for beginners or public nights because experience required to find correct eye placement.


Peter Vercauteren


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