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Impressions of the 10mm Siebert MonoCentric ID

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#1 BillP

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Posted 02 May 2012 - 09:06 PM

Thanks to the generosity of a fellow CNer, I had the opportunity to try out one of the Siebert Monocentric ID eyepieces (http://www.siebertoptics.com/Mono.html). I performed casual testing over several nights on Mars and the Moon using both my XT10 f/4.7” Dob and by TSA-102 f/8 refractor. I compared it to the performance of the 10mm Astro-Physics Super Planetary (AP-SPL) and also gave a few tests against the Pentax 10mm XW.

Overall the construction of this eyepiece is typical of Siebert’s other wares which is built sturdily but very utilitarian in look and feel. The top housing is Derlin and the barrel is Aluminum. Overall the eyepiece is very light. The field stop is not a knife edge but rather a broad flat surface blackened with paint to stop any reflectivity. So a little crude in execution for this component which then provided not so precise of a uniform edge while viewing. I did not measure the eye relief or AFOV of the Siebert, however the ER seemed adequate and it was not difficult to see the entire AFOV, and the AFOV appears to be around 35 degrees, or slightly less than a standard ABBE.

Observing Mars with both the TSA and the XT10, it was necessary to do the testing using two different Barlows as a 10mm eyepiece does not produce sufficient magnification in either scope. A TeleVue 2x and a Siebert 2.5x Barlow was used. The AP-SPL showed the most detail, contrast, and least scatter of the three eyepieces. The Siebert was very close however when using the TeleVue 2x, with the Pentax XW, while putting up a very good showing, could not compete so closely to the others showing more scatter from its complex design which washed out some of the finer details visible in the other eyepieces. The primary differences between the AP-SPL and the Siebert Mono ID were a less pronounced showing of Martian details with slightly more scatter. As example, in both eyepieces the polar cap was revealed very prominently, along with the dark region surrounding it. However, the Mare Sirenum, Solis Lacus, and Mare Erythraeum surface features were less prominent. Solis Lacus in particular was only hinted at with the Siebert Mono ID while clearly evident in the AP-SPL. The Pentax XW would not reveal Solis Lacus.

Moving to the Moon, both the AP-SPL and Siebert appears to be much closer in performance than they were on Mars. However, after a lot of detailed observing of highland formations and crater walls and ejecta patterns and finally faintly lit structures just outside the terminator, it became clear that the AP-SPL was showing a slight edge over the Siebert Mono ID. Compared to the Pentax XW, the Siebert Mono ID showed the smallest details just ever so slightly better defined. The difference however was extremely small and required a lot of effort to tease this difference out. What was overwhelming though for the Moon was the expansive AFOV of the Pentax XW where the view was sharp to the edge, providing a jaw-dropping view compared to the other more narrow field eyepieces. This in itself, for the Moon, made the Pentax seem more impressive overall.

Considering the off-axis performance, the Siebert Mono ID was performing a less well than a TMB Supermonocentric. In the XT10, regardless if the Paracorr was in place or not, only about the central 1/3 of the FOV or even slightly less was un-aberrated and sharp. The AP-SPL by comparison showed about 60% or slightly more of its FOV sharp. In the TSA’s f/8 the Siebert Mono ID improved some with approximately 75% of its FOV being sharp and the AP-SPL showing probably more than 95% sharp. Overall, I found the usable AFOV in the AP-SPL sufficiently large for productive observations in the undriven XT10. The Siebert Mono ID’s usable FOV in the fast XT10 was just too small however and was quite a burden for enjoyable or productive observing at the high magnifications in play (300x). So like the TMB Monocentrics, the Siebert Monocentric ID really needs either a long focal ratio scope or a scope with a driven mount to be productive and easy to use. As a side, neither eyepiece with either Barlow showed their full FOV. In both the field stop became less distinct, fuzzy, and showed reduced illumination at the field stop. Most likely the field lens of each was not large enough to catch the entire light cone from the Barlow so their FOVs showed vignetting. The Pentax of course had no such problem and showed the full FOV distinctly to the edge with either Barlow.

When moving from the TV 2x to the Siebert 2.5x however, things changed radically. Being called to produce the extra magnification using the 2.5x Barlow, making the eyepieces effectively 4mm eyepieces, the Siebert Mono ID was not able to produce near as crisply defined of an image as was the AP-SPL. I have noted this behavior before in eyepiece tests, where the stress of a Barlow on the eyepiece design (or the precision of its lenses figures) often separate the more capable from the less capable eyepieces. So in this instance, the Siebert Mono ID could not produce as sharp of an image. Moving the scopes back to Mars, this behavior was replicated with most all of the Martian detail being washed away, except for the polar cap, with the Siebert Mono ID with a 2.5x Barlow, while the AP-SPL still produced a nicely sharp and detailed image of all the Martian features.

As a specialty planetary eyepiece, the Siebert Monocentric ID appears to be a fair alternative to the much more expensive and harder to find TMB Monocentrics. However, its usable un-aberrated AFOV in fast scopes really makes it not recommendable unless one has a driven mount where the planet can be kept directly on-axis. In addition, while the build is adequately sturdy the field stop was somewhat crudely executed and did not provide the knife-edge performance typical of mass production eyepieces. While this may be nit-picking, given the $150 cost, some aspects of the build might not be considered worth the investment to some observers. From a purely performance perspective though, at its native focal length up to 2x Barlowing it was able to keep fairly close in on-axis performance with the top-shelf AP-SPL. In either case, definitely an eyepiece needing a driven scope to realize its potential.

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#2 thrawn

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Posted 02 May 2012 - 09:10 PM

Let me be the first to say that this is great great stuff, and thanks for the review.

So this is what we can make of an edmund triplet.

#3 Richard Low

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Posted 02 May 2012 - 09:28 PM

Nice review. Thanks for sharing your findings with us, Bill. I always wondered about the Siebert monos vs TMB monos, now i know! Some monos are prone to ghosting, are there any ghost with this one?

#4 george tatsis

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Posted 03 May 2012 - 02:44 AM

Bill,

I can't thank you enough for comparing these two eyepieces,as it had always been a mystery to me how well it would compare with a premium piece of glass.Thanks again!

George

#5 Sarkikos

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Posted 03 May 2012 - 07:32 AM

Bill,

Thanks for the review. I've been curious about the performance of these Siebert Monos for some time now.

Mike

#6 BillP

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Posted 03 May 2012 - 08:43 AM

Nice review. Thanks for sharing your findings with us, Bill. I always wondered about the Siebert monos vs TMB monos, now i know! Some monos are prone to ghosting, are there any ghost with this one?


I didn't do any ghosting or flare tests specifically. But will give that a try this weekend if the weather permits. I doubt any ghosting though as it would have revealed itself IMO on Mars. Pretty hard I think to get a monocentric to ghost given all elements cemented. I doubt eyeball glint would happen either as small eye lens and fairly close ER and top surface is convex. With all three parameters like that, usually not a recipe for glint.

#7 SpaceOtter

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Posted 03 May 2012 - 10:10 AM

The 10mm monocentric is best used in scopes f/7.5 and slower, according to the description on the website. The rest of the series, however, is best when used at f/4 minimum. I wonder if impressions of the 10mm might not apply to the rest of the monos, though my hunch is they are ultimately similar.

#8 eastwd

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Posted 03 May 2012 - 11:01 AM

Thanks, Bill! VERY useful information, particularly the comparison of how well each eyepiece handled specific features on Mars. Been looking at the Siebert monocentrics (and the "Planespheres") on Harry's website and wondering about them. This answers a lot of my questions.

#9 BillP

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Posted 03 May 2012 - 12:16 PM

Do not touch any sphere singlet unless you have a tracking mount. Usually only central 10 deg sharp in those. But it is a wonderful sharp! I have some home make ones using Edmunds glass.

#10 Scott99

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Posted 03 May 2012 - 12:55 PM

very cool, thanks for posting! Always good to welcome another member to the 3-element eyepiece club. (right now only three other lines, right? SPL, TMB supermono, RKE)

#11 Sarkikos

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Posted 03 May 2012 - 01:20 PM

Always good to welcome another member to the 3-element eyepiece club. (right now only three other lines, right? SPL, TMB supermono, RKE)


... Kellner. :grin:

Mike

#12 Scott99

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Posted 03 May 2012 - 02:30 PM

very cool, thanks for posting! Always good to welcome another member to the 3-element eyepiece club. (right now only three other lines, right? SPL, TMB supermono, RKE)


absolutely, all the Kellners are in there!

#13 kepheus

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Posted 04 May 2012 - 04:16 AM

Great review!
I have been waiting for a report on the MonoCentric ID eyepieces for a long time.
Thank you very much, Bill.

- Brend

#14 PJ Anway

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Posted 04 May 2012 - 06:53 AM

Very nice report Bill, thanks for posting it! I had a set of TMB monos and they performed very well in my 4" f/10. However, because I already had a set of CZJ orthos, they seemed redundant and were eventually sold in favor of the "wide" FOV. :grin:

#15 BillP

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Posted 11 May 2012 - 09:53 PM

I've had a bunch more observing time now with the Siebert, and all of it "quality" time (i.e., all with the TSA-102 on excellent evenings). With this new batch of observing I have some new impressions...plus I spent most of this time with Saturn. I'm actually seeing a bit more contrast through the Barlowed Siebert than through the Barlowed AP-SPL. The Cassini division was more starkly portrayed and appeared blacker through the Siebert. In addition, the colors and gradations in the polar regions of Saturn were more detailed and more colorful in the Siebert. So overall, spending lots of time on Saturn through the TSA, I would say the Siebert has a slight edge. Now as we go off-axis it is not as well controlled as the AP-SPL. However, almost all the off-axis degradation was due to field curvature using the TSA-102 at f/8. Once I moved Saturn about 35-40 degrees off-axis, the field curvature became enough to need a slight turn to re-sharpen the image.

Anyway...very impressive on-axis performance considering it just out did an eyepiece costing over 3x as much. As I said, only point needing some more attention is a little better construction with the field stop, but other than that a whole lot of bang for the buck for the planetary purist who has a longer focal ratio scope and tracking to handle the rather limited FOVs monocentrics deliver. :waytogo:

#16 george tatsis

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Posted 11 May 2012 - 10:46 PM

I've had a bunch more observing time now with the Siebert, and all of it "quality" time (i.e., all with the TSA-102 on excellent evenings). With this new batch of observing I have some new impressions...plus I spent most of this time with Saturn. I'm actually seeing a bit more contrast through the Barlowed Siebert than through the Barlowed AP-SPL. The Cassini division was more starkly portrayed and appeared blacker through the Siebert. In addition, the colors and gradations in the polar regions of Saturn were more detailed and more colorful in the Siebert. So overall, spending lots of time on Saturn through the TSA, I would say the Siebert has a slight edge. Now as we go off-axis it is not as well controlled as the AP-SPL. However, almost all the off-axis degradation was due to field curvature using the TSA-102 at f/8. Once I moved Saturn about 35-40 degrees off-axis, the field curvature became enough to need a slight turn to re-sharpen the image.

Anyway...very impressive on-axis performance considering it just out did an eyepiece costing over 3x as much. As I said, only point needing some more attention is a little better construction with the field stop, but other than that a whole lot of bang for the buck for the planetary purist who has a longer focal ratio scope and tracking to handle the rather limited FOVs monocentrics deliver. :waytogo:


Very impressed with the outcome Bill! I never expected the Siebert to put up that big of a fight and outdo the SPL. :shocked:

Wish Jupiter were visible ,because that would be the ultimate planetary test. :question:

Thanks Bill!

#17 Jim Rosenstock

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Posted 12 May 2012 - 06:17 AM

Wish Jupiter were visible ,because that would be the ultimate planetary test. :question:


Hmmmm...I'd say each planet is its own test! :cool: What works best for Mars might not for Saturn or Jupiter.

I'm finding that the case with my Ball eyepieces...exquisite aesthetics on Jupiter; Mars and Saturn (so far), not so much...

Good for Harry that he seems to have a (specialized) winner here! :bow: I only wish he had shorter focal lengths that didn't need barlowing. (I think he's using "stock" Edmund triplets and hand-machining the bodies...)

Jim

#18 jrbarnett

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Posted 12 May 2012 - 08:55 AM

Jim:

I think you're right about origin of the optical group.

I'm wondering if these "monocentrics" are really "moncentric" in the strict sense as a result.

http://www.edmundopt...tic-lenses/1928

http://www.edmundopt...tic-lenses/1725

Not every cemented triplet is monocentric.

Regards,

Jim

#19 leonard

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Posted 12 May 2012 - 01:02 PM

Hello ,

>>>>>>>> I'm finding that the case with my Ball eyepieces...exquisite aesthetics on Jupiter; Mars and Saturn (so far), not so much... <<<<<<<<<<<


Hi Jim , any idea why this is ???????


Leonard

#20 Sean Cunneen

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Posted 12 May 2012 - 05:15 PM

Charles Hastings wrote an article on his eyepiece design in ATM 1. IMHR , Hastings was an astronomer and felt his design was an improvement over the Steinheil (at least he thought so). At the time lots of folks didn't like the Steinhiel for it's ghosting and narrow field.

#21 Jim Rosenstock

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Posted 12 May 2012 - 07:48 PM

Hello ,

>>>>>>>> I'm finding that the case with my Ball eyepieces...exquisite aesthetics on Jupiter; Mars and Saturn (so far), not so much... <<<<<<<<<<<


Hi Jim , any idea why this is ???????


Leonard


Dunno, Leonard. Maybe a couple of good nights with Saturn will change my mind... :cool:

I just haven't had the Ball eyepieces make me say "Wow!" compared to my other eyepiece views on Saturn....and this was a regular occurence with Jupiter a few months back....

One thing I really like about Ball eyepieces on Jupiter, is that Jupiter's moons often are helpful in centering the ten-degree "sweet spot" where a Ball image is sharp, and the "fisheye effect" on off-axis moons is often quite interesting....even adds dimensionality, sometimes.

Messing around with Ball eyepieces certainly isn't for everyone. Perhaps I should take up a hobby.....wait!--this is my hobby! :cool:

Jim

#22 MRNUTTY

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Posted 29 June 2012 - 06:44 AM

Bill, in your first assessment, it seemed the Siebert did better with the TV 2x (I'm thinking it was a powermate) than with the Siebert 2.5x. Is this merely an issue of magnification, or is the Siebert Barlow somehow lacking? I have a couple Siebert EP's and a 2x barlow on order and I'm wondering if I should just stick to my TV powermate of the same power instead. Awesome review Bill!

Also, really appreciate any insights into F ratio vs performance. With 8 scopes (? How did that happen???) of various F ratios, the SCT's with over F/7 seem best suited for these EP's.

#23 BillP

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Posted 29 June 2012 - 09:28 AM

The TV 2x was a Barlow. I usually do not prefer Telecentrics or Powermates for planetary observing as I can see the extra scatter they produce from twice the glass they have compared to Barlows.

The Siebert 2.5x I have is excellent optically and I do not consider the TV 2x to be any better optically. Only difference between them is tonal qualities, the 2x being warmer. Both extremely sharp.

I can only conjecture as to why the Siebert Mono did not handle the 2.5x Barlow as well as the AP-SPL. I have seen this behavior before with eyepieces and some lines just can't take high magnifications as well as other eyepieces. The Sterling Plossls are like that for me also...they perfom increadibly at their native focal lengths and normal Barlowing, but push then with a 4x or 5x Barlow for planetary and they don't do as good as others. I attribute it to probably being something with either the polish or figure of the lenses, probably the latter. Nothing is perfect in every way unfortunately.

#24 Sarkikos

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Posted 29 June 2012 - 09:36 AM

BillP,

The TV 2x was a Barlow. I usually do not prefer Telecentrics or Powermates for planetary observing as I can see the extra scatter they produce from twice the glass they have compared to Barlows.


This is good to know. From time to time I consider acquiring a Powermate, but have always resisted because of the price. Now I have another reason to resist. :grin: I hardly use Barlows anymore except as an OCA in my binoviewer or filter wheel. Otherwise, once in a great while I might Barlow single eyepieces to observe bright planets.

Now I have absolutely zero reason to buy any Powermates.

:waytogo:
Mike

#25 MRNUTTY

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Posted 29 June 2012 - 02:26 PM

I've only used my powermate a couple of times. I prefer discrete EP FL's to using a Barlow. But in the case of the Siebert's I figured if I was going to buy a Barlow, I would buy one for the set of EP's that was made by the same person the EP's were made by. Contrasted to vendors, and unclear manufactures where the source of individual components is unknowable.

I bought the powermate early on when I thought I would be Barlowing as a regular process.


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