Siebert Star Splitter

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Brand and Model:Siebert Star Splitter
Price ($USD):$99
Type:Modified Orthoscopic
Focal Length:5.9mm mm
Barrel Size:1.25
Apparent FOV:65.0 degrees
Field Stop Dia.:0.0 mm
Eye Relief:10 mm
Weight (lbs):

Vote Highlights Vote
Siebert Star Splitter
I was surprised that only two votes had been made for this EP series, so I thought I should add my own impressions. I have compared the Star Splitters to various Plossls, Orthoscopics, Burgess TMB, Celestron Ultima, and modern Kellner type planetary EP's. The Star Splitter became my favored planetary EP for various reasons, the major ones being that they were more comfortable to view through without sacrificing sharpness and contrast while opening up the FOV. True, you can buy the UO Orthos for only $60, but the major advantages of the Siebert Star Splitters make them worth the extra $40. The EP that seems the most like the Star Splitter is the Celestron Ultima/Baader Eudiascopic (basically the same EP except for labeling) in quality of image, but those EP's are only comfortable down to around 10mm or 12.5mm. I needed an EP to extend downward from there and remain comfortable, so the Star Splitters have replaced almost all my other EP's below 10mm. The Star Splitter series allow FL changes in small steps, so you can get just the right ones you need. I own six of them, and am considering ordering a seventh one, the shortest one at 2.9mm.

These EP's are VERY light due to the aluminum barrels. They are therefore the type planetary EP's you need to load up your EP turret without overloading your focuser or causing a balance problem with your scope. Also, a set of 5 of these EP's will probably not exceed the cost of your EP turret. The EP barrels are smooth with no safety undercuts, so I am allowed to get them EXACTLY parfocal with each other. This is something else that turret owners should consider. It allows me to QUICKLY find the right mag for star splitting without having to refocus between each EP. The savings in cost over the other super premium planetary EP's will probably allow you to buy that nice Van Slyke, Tak or TEC EP turret you've been wanting. The soft aluminum barrel will allow the holder screw to bite in and not let the EP slip out as chromed brass EP barrels have a tendency to do. Thus I am freed from the cost and weight of parfocal rings. Just store the EP turret with the Star Splitters in their parfocal positions, and you only ever need clean the eye lens.

Overall Rating: 10
Optics:10 Value:10
Weight: 1 (Unreliable Vote)
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Siebert Star Splitter
I have a 4.4mm and 6.4mm Star Splitter binoviewer pair. They have 5 elements with a Barlow front element. The sharpness, contrast and color saturation are similar to Ultima EP's, but with better eye relief and larger eye lens and will work better in fast focal ratio scopes. I also have the 8.9mm Star Splitter in a binoviewer pair. It is a 3-element design that works best in slow focal ratio scopes. It has higher contrast and is sharp to the edge in my f/15 Mak-Cass with Siebert Black Night 22 binoviewer. It is my sharpest and highest contrast EP for long focal ratio scopes, and the light transmission is very high. It maxes out the resolving power on bright globular clusters and is unrivaled in lunar viewing, and weighs almost nothing and is much shorter than the 7.9mm and shorter FL Star Splitters. The 8.9mm and 9.9mm Star Splitters are for long focal ratio scopes as they are triplets. I believe that all the shorter FL Star Splitters are designed from these two triplets, which become 5-element designs when the telenegative doublet (Barlow) is added to the front. 7.9mm and shorter Star Splitters have a long EP barrel that takes a dew heater strap very well and they heat up and clear much faster than my heavier brass EP's. They have no safety undercut, so they work well in compression type self centering EP holders that are common on the best binoviewers. The Star Splitters are my first choice in a high power binoviewer EP. You need light weight and ability to handle heater straps well in that application. Eye relief is long enough to keep your eyelashes off the lens, but not so far as to make positioning of your eyes difficult. There is no blacking out and kidney beaning as you move your eye around. I tried the 9mm TMB as a binoviewer pair, but had heater strap problems and it was much harder to hold the proper viewing position with both eyes. The 9mm TMB worked fine as a mono EP in my fast f/6 refractor. The light weight of Siebert EP's make them ideal for binoviewing, and they are less expensive to buy than other EP's with similar optical performance. The Star Splitters should be excellent companions to the Siebert Ultra series, but I pair mine with the Axioms and Ultimas that I already had in 12.5mm and longer FL's. That's why I can say that The Star Splitters are equal in performance to some very highly regarded EP's.

Overall Rating: 9
Optics:9 Value:10
Weight: 1 (Unreliable Vote)
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Siebert Star Splitter
[Note: Vote moved from description by webmaster]

First Impressions and First Light…

After several weeks (Harry had to construct it since on wasn’t available on the shelf), I received the Siebert 5.9mm Star Splitter Modified Orthoscopic. It is touted to have a 65 degree afov with 10mm eye relief. When it arrived is appeared just as the photo on their website – hand machined aluminium body with an inset on the top in a darker rubbery material which housed the lens. The machining was done well (i.e., uniform and accurate) and buffed leaving the small lathing lines from the machining (i.e., the external housing is not buffed to a high shine high smoothness like you see on the typical chromed brass barrels of standard production eps). The ep was large relative to the UO HD, fitting in the full width of my palm. Optical elements showed a nice purple/violet coating with the overall ep feeling light for it’s size (actually a welcome thing since overly heavy eps tend to be less favorable on a Dobsonian because there are no counterweights to offset significant weight additions). The bottom had a large field element which I presume is a built-in barlow for the ep, similar to what TeleVue does on some of theirs, as well what we see on the Orion Stratus and similar wide-field designs – an effective way to achieve better eye relief for a given focal length. Overall it looked and handled very good.

OK, we are finally getting to first light. So on a relatively dark evening in March I took my f4.7 Orion 10” XTi Dobsonian out to compare the new Siebert 5.9mm Star Splitter (SS) to the 6mm UO HD. I also brought out the 4.8mm TV Nagler for a general impression difference. I didn’t want to make too much of a comparison to the Nagler since they were different focal length eps. So I placed the scope and eps outside and left them there for an hour thermal adjustment period. It was 70 degrees in the house and probably 45 degrees outside, so I’d need at least an hour. I had also collimated the Dob the weekend before.

Once outside I set up the Orion’s Intelliquest (GOTO system), then checked out my diffraction rings on a bright star. I did this to ensure the allighment was still good, and I also do this to determine how well the mirror and other optics are thermally adjusted as you can easily see the thermal ripples in the diffraction pattern if the scope is not in thermal equilibrium with the environment. The star test confirmed the allighment and thermal balance were good.

So what should I test as a first object to compare the UO HD with the SS? Saturn was high overhead. Perfect. The Saturn test was excellent. The UO HD provided an outstanding image as usual, Cassini division clearly visible around the majority of the ring (sometimes difficult in front portion of the ring) and some good cloud belts visible. The planet’s shadow on the rings was also very clear, giving the nice three-dimension impression to the planet orb. I now popped in the SS. It only required a minor refocus over the UO HD. I didn’t know what to expect, hoping for the best but prepared for the worst. Actually I was just hoping it would be equal in terms of resolution to the UO HD. If it was equal, then for just $20 more than the HD I could move from and afov of 45 degrees to 65 degrees, and that would be great.

I made the initial focus of Saturn using the rack and pinion, then moved to the fine focus afforded by the Clear Skys Fine Helical Focuser Adaptor. This adaptor fits in 2” focusers and provides fine focus for 1.25” eps only. I have found this affordably priced accessory to be the best accessory I have for the scope. I was astonished how easy, fast, and precisely it allows you to find the exact focus for an ep. Invaluable for any high power work. Bottom line is lots more satisfying observing and almost zero focus time since I got this accessory. With Saturn quickly at fine focus in the field of view, the first impression was…it’s sharper! The Cassini Division was nice and clear fully throughout the visible ring system. Boundaries between illuminated planet and shadows cast on the rings were more distinct, and cloud banding more pronounced than in the UO HD.

I was really surprised. I had not expected it to best the UO HD, not in resolution anyway. But it did. How much? At the moment, with this initial impression I would say moderately significantly. Not what I might characterize as an order of magnitude, so perhaps by a half an order of magnitude. To explain better what I mean when I subjectively say it was half an order of magnitude better, what I mean is as follows. When I am observing I do notice a resolution difference between the TV Plossl and the RKE and the UO HD when they are compared to each other relative to Saturn. But after the observing session is over, the impression that is left with me is that I recall they were different, but I can’t recall the experience to say that it was a real “remembered” difference. The picture does not remain in my memory. So they were really objectively probably just close…a tad better resolution to the UO HD…enough to be obvious while observing and comparing. The difference between the UO HD and the Siebert SS however was more than that. Well after the observing session it is easy to recall the image of Saturn with its greater detail. So somewhere around a moderate increase in apparent resolution. Good!

Next I moved to splitting some doubles. First off I chose Polaris. Not because it is difficult, but because the companion is so dim relative to the primary. Polaris is magnitude 2 and its companion is magnitude 9. So a nice light throughput comparison. The UO HD showed the companion fine; dim, but there. The SS showed it as well. I could not discern any significant difference. Perhaps a little better in the SS, but can’t say. So I’ll leave that determination to an evening with the Trapezium and trying to catch component F, which is usually difficult in my light polluted observing area given how close it is to its brighter component. So this was good also, equal to the UO HD.

Next I moved to Mizar as well as several of the doubles in Bootes (using the Intelliquest to get there). In Bootes I checked Iota, Kappa, and Xi. Xi is the closest of the bunch with a 6.9 arc second separation. All split easily in both the UO HD and the Siebert SS. This, of course I expected after viewing Polaris. While I didn’t think there would be any problems splitting these doubles, I was surprised to notice that the Siebert SS provided a more pinpoint star image. I guess that should have been expected given it resolved more on Saturn. But I have noticed that this is not always the case. I have found that an ep will do a better job on Saturn even if it is not as sharp in resolution if it has better color correction. Recently I did a bench test with several eps using a photo resolution test target. The ep which resolved the most lines per millimeter on the test target performed miserably on Saturn. It was then that I noticed that this high resolution ep (high resolution for black and white) had noticeable color aberrations both on and off axis. From that point I learned the importance of color correction to resolution on extended objects such as planets.

Next I moved to M36 and M37 in Auriga. They were available between two large trees from my yard. Using the Intelliquest I dialed them in and pushed to scope to the coordinates with ease. Both the UO HD and the Siebert SS provided good views. I think perhaps the sky background between the stars seemed a tad darker in the UO than in the SS, but it was difficult to determine if that was really true. It appeared a slight bit darker, but I’m not sure if it was because of the optical phenomenon I described earlier relating to contrast appearances when switching from a narrower to a wider afov ep. Anyway, at this point in the evening the Orion Nebula was well behind an offending tree so I will save a field darkness or contrast assessment until an evening when I can target that. I like using the Orion Nebula for this purpose because of the many fine gradations in the whisps and molts of the nebula. Just makes it easier for me to make those types of determinations.

Getting back to M37 with its many fine dim stars throughout the cluster, what was a particular advantage to the Siebert SS over the UO HD was the larger field of view. It was quite pleasing to see so much of the cluster at this high power (200x). The finer pinpoints of the SS also made it a better observing experience. And when I barlowed the SS up with the Klee (561x), even at this extreme power it was still a pleasant view into the star cluster. It was quite a pleasant surprise to be able to work at such a high power on an open cluster. I attribute the 65 degree afov the SS has to this.

So in my barlowing of the SS (and the UO HD), it was apparent that both of the eps barlow extremely well. Light throughput was not diminished beyond what was expected from the higher power, and the images held up extremely well with stars remaining very point-like, especially in the SS. With the Barlow attached, I moved the scope back to Saturn to see how it fared under barlow at this extreme power setting. As expected, the image was very much larger and a bit softer. I expected a softer image since this put me at 56x per inch of aperture, so in excess for this night’s seeing, which was good but not excellent. Plus 56x per inch is pushing it for any scope, especially a fast production Newtonian. But it was pleasing that the image was still very good. The Cassini gap being extremely pronounces plus other markings now visible along the outside of the rings. Overall I would put the SS as moving from moderately significantly better in resolution over the UO HD, to being a “tad” or noticeably better under barlow.

The final test I wanted to do was an edge-of-field star test. The UO HD performs extremely well here. It does get some bloating of the star image towards the very edge, but not much, maybe 10% bloating at the extreme edge. With the larger afov of the Siebert SS, I expected nothing so good, especially since this was on a fast scope at f 4/7. I picked a random medium bright star in the field near Saturn (off towards the Beehive), and tracked it through the field of the SS. To my extreme surprise there was only minor bloating as well, maybe 10% towards the last 5-10% or less of the field. I was actually in shock it was so minor. And that minor bloat was not all the way around. So at some parts of the field the star exhibited no bloat right to the edge. So quite impressive! Going back to M37, I re-verified this. So with the bloating so minor, as it is in the UO HD, it was not even apparent looking over the stationary cluster throughout the field of view that any star was anything but a point. So an extremely satisfying view in this very fast scope all the way to the edge.

Overall, the Siebert Star Splitter excels over the UO HD, and it does so significantly when we factor in the larger afov and all for only $20 more in cost. Again, let me caution that these are “first light” impressions over a weekend of use for the 5.9mm specimine only. As I said before, each optical design has its own unique strengths. So perhaps over the next few weeks these strengths will play out between the UO HD and the Siebert SS. But for now, in a first impression, I would say that the Siebert Star Splitter series has the potential to “replace” my University Optic HD Orthoscopics! What it definitely means at the moment though, before doing any actual replacing of ep lines, is that I can confidently move on to purchasing a few other focal lengths of the Star Splitters. And if each of these similarly outperforms their UO HD counterparts, there may be something very special here in the Siebert Star Splitter Modified Orthoscopic design for fast Newtonian users.

By-the-way, I did do a very cursory comparison of the SS to the 4.8mm Nagler. As expected, since I know the differences well between the Nagler and the UO HD, overall the Nagler produced a less resolute and less contrasty image exhibiting less light throughput than the other designs I have. The Nagler is slightly less resolute than the UO HD, which means a lot less (but still good) when compared to the SS. The edge of field performance on the Nagler is also not as tight at the UO HD or the SS. But the Nagler still has some intrinsic unique characteristic strengths in the image it produces, like the Plossls and RKEs and Erfles each also do, which means for me that this Modified Orthoscopic design should not replace the Nagler. But overall and in general, the Siebert 5.9mm Star Splitter ranks much higher in observational qualities to the 4.8mm Nagler Type-1.

Next month I will post an update to this First Light review as I get more experience with the Star Splitter under my belt. In that update I’ll pay more attention to color correction (which seemed perfect), actual afov size (which seemed a little less than 65 degrees), and other performance characteristics. To end the viewing this evening however, I wanted some observational “desert” be the last taste for my night of observing. So I turned the scope back to Saturn, took the Star Splitter and placed a Burgess Optics #82A light blue filter on the bottom, and took in some last views of that exquisite planet for the evening’s memories. And it was…spectacular! Being in a moderately light polluted area, I find the light blue color filter does wonders as it darkens the background sky without losing me many (or any) stars from the minimally reduced light throughput. I find it very much more pleasing than a pollution filter since it gives me a much brighter image. Plus the light blue doesn’t detract from most images. So there she was, absolutely stunning with her atmospheric bands and ring system in all their splendor and much accentuated with the filter in place. A most wonderful last image for the evening with this pleasantly surprising new eyepiece.

Happy Observations!

ps – FYI, I have no interest or relation to Siebert Optics or any other private or commercial photographic, optical, or astronomical entity. I am simply a visual astronomy hobbyist enjoying the hobby from his back yard.

Overall Rating: No Vote
Weight: 1 (Unreliable Vote)
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