TheSkySearchers

102 mm Refractor versus 140 mm Maksutov; Vixen ED102 vs OMC140
by John Baars

102mm refractor versus 140mm Maksutov Vixen ED102S vs. OMC140 Preface Some years ago I bought an older Japanese Vixen ED 102 f / 9 refractor from the Nineties. Reason: I wanted to get rid of the long cooling time of my OMC Maksutov, but at least retain the image quality of the Maksutov. Preferably with...
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Fine article and well illustrated. The conclusions are about what I would expect based on optical science. Also a nice job demonstrating (among other things) that Maksutovs are good on DSOs.

One point of clarification, although Rutten may have designed this scope, it is not a Rutten-Maksutov Mak if it has a silvered spot secondary on the back of the corrector plate. That is a Gregory-Maksutov. The Rutten-Maksutov has a separately curved secondary which gives an additional degree of freedom for the optical design. Your photo indicates one can see the secondary spot on the corrector, so if I'm interpreting the situation correctly it is a Rutten designed Gregory-Maksutov, likely.

A great article John, thank you for putting this together.

notFritzArgelander wrote: ↑Sun Jan 26, 2020 10:08 pm Fine article and well illustrated. The conclusions are about what I would expect based on optical science. Also a nice job demonstrating (among other things) that Maksutovs are good on DSOs.

One point of clarification, although Rutten may have designed this scope, it is not a Rutten-Maksutov Mak if it has a silvered spot secondary on the back of the corrector plate. That is a Gregory-Maksutov. The Rutten-Maksutov has a separately curved secondary which gives an additional degree of freedom for the optical design. Your photo indicates one can see the secondary spot on the corrector, so if I'm interpreting the situation correctly it is a Rutten designed Gregory-Maksutov, likely.

It belatedly occurs to me that if the silvered secondary were a meniscus cemented to the back of the corrector then it could be a Rutten designed Rutten Maksutov. Would it be possible to check and see if the reflective coating were on the corrector directly or with and intervening meniscus? Thanks.

PS There is a review on another site that says that while the layout is Gregory-Maksutov, one of the surfaces is aspheric. So I'm curious.

Thanks for a thorough and well executed review John! Your experience matches mine closely. For me it was 80mm ED vs 127mm Mak. The Mak felt darker than it should on DSOs. Jupiter view was sharper in 80mm, but Mak resolved more details at the moments of better seeing.

From Orion Optics UK page:
The design is not a standard all spherical one with a main mirror the same size as the corrector. That is the traditional Maksutov design but, it lacks off axis performance and suffers from coma. The OMC140 has an ellipsoidal primary which is over 12mm larger in diameter than the Maksutov corrector. This added aspherisation of the primary allows much wider flatter fields to be achieved but it virtually eliminates coma.

https://www.orionoptics.co.uk/OMC/omc140maksutovca.html

Lady Fraktor wrote: ↑Mon Jan 27, 2020 4:40 am From Orion Optics UK page:
The design is not a standard all spherical one with a main mirror the same size as the corrector. That is the traditional Maksutov design but, it lacks off axis performance and suffers from coma. The OMC140 has an ellipsoidal primary which is over 12mm larger in diameter than the Maksutov corrector. This added aspherisation of the primary allows much wider flatter fields to be achieved but it virtually eliminates coma.

https://www.orionoptics.co.uk/OMC/omc140maksutovca.html

Thanks. I dyslexically missed that. It is then neither Gregory-Maksutov nor Rutten-Maksutov both of which have all spherical surfaces but is rather a unique and proprietary design based on a Gregory-Maksutov layout. Thanks again!

H. Rutten designed the optics as far as I know, including the ellipsoidal primary.
But there is more, he also designed the baffle system, which has some 15 mini-baffles within the main central baffle.
The famous Wolfgang Rohr ( at least he is well known all over Europe) tested an OMC140:
http://r2.astro-foren.com/index.php/de/ ... tografisch
Here one can read the following:

The OMC140 has an ellipsoidal mirror which is over 12mm larger in diameter than the Maksutov corrector. This added aspherisation of the primary allows much wider flatter fields to be achieved, but it virtually eliminates coma.

Furthermore one can see an intersection of the baffle in the link.

John Baars wrote: ↑Mon Jan 27, 2020 8:12 am H. Rutten designed the optics as far as I know, including the ellipsoidal primary.
But there is more, he also designed the baffle system, which has some 15 mini-baffles within the main central baffle.
The famous Wolfgang Rohr ( at least he is well known all over Europe) tested an OMC140:
http://r2.astro-foren.com/index.php/de/ ... tografisch
Here one can read the following:

The OMC140 has an ellipsoidal mirror which is over 12mm larger in diameter than the Maksutov corrector. This added aspherisation of the primary allows much wider flatter fields to be achieved, but it virtually eliminates coma.

Furthermore one can see an intersection of the baffle in the link.

Fine, well, and very good. Not arguing that Rutten didn't design the OMC140. I'm simply clarifying that the OMC140 is not a Rutten-Maksutov. One can see from the linked diagrams that the OMC140 is laid out as a Gregory-Maksutov. It doesn't have a secondary separate from the corrector as the diagram in your link shows. The separate secondary design as in Lourdes linked diagram (originally from Rutten's book) is what makes a Rutten-Maksutov what it is.

Rutten's idea of an aspheric ellipse ideal oversize primary is quite ingenious and it is very nicely baffled indeed. Rohr's test data are quite impressive. I compared them with the theoretical data in Rutten's book and it looks excellent.

I'm simply hoping that folks don't confuse this apparently Rutten designed aspheric Gregory-Maksutov system with a Rumak-Maksutov.

To notFritzArgelander:
I have changed the text in:

The OMC was designed by H. Rutten as an aspherical Gregory- Maksutov and is internally equipped with a sophisticated baffle system.

Just to be sure.

John Baars wrote: ↑Mon Jan 27, 2020 6:38 pm To notFritzArgelander:
I have changed the text in:

The OMC was designed by H. Rutten as an aspherical Gregory- Maksutov and is internally equipped with a sophisticated baffle system.

Just to be sure.

Well, that's certainly as precise as one can get!

I know that some folks have been confused by the advertising and have claimed it as something else.

A nice review

Hello John,

thank you for the report you have supported with your excellent sketches!

Best,
JG

Thanks John, I enjoyed this.

Thank you for the fine review and comparison. The Celestron/Orion refractors made by Vixen years ago were outstanding instruments. My first scope was the base model Orion by Vixen 102. I believe the Orion/Celestron by Vixen 102mm series had three OTAs, my base model achromat that acted like an APO, the ED102 you reviewed, and the legendary 102 Flourite APO. All were doublets. I did compare my scope against the ES 152 and the 102 produced sharper stars. I couldn't get over how good this reasonably priced scope really was and I was not alone as I connected with other 102 owners at the time. I actually wanted to step up and buy the fluoride 102, but I just couldn't see paying what they were asking for them when there were many quality and affordable triplets coming on the market at that time. Your review was a nostalgic reminder of a great line up of refractors by Vixen.

Hello John,
Nice to hear from you. Do you still have your Vixen?

I have been surprised too by the excellent performance of this refractor. And so did the optician (a very well known one in the Dutch astronomy society) who re-coated the frontlens for me. He told me never ever to get rid of it and if I did, I should call him...
I am the third owner, I am glad to hear from a first owner of that Vixen line. When these Vixens came out I was still busy scouring the Universe with ATM Newtons.

When Vixen (and other companies) started making the Fluorite doublet line, Fluorite was still a very scarce and expensive crystal. It became that popular that soon a shortage developed on the economic market. Vixen responded with the f/9 ED doublet refractor, made of less expensive glass. The f/9 was necessary to achieve almost the same CA as the Fluorite one. (CA in this f/9 is only seen at the edges of a defocussed star) Soon after newly made, less expensive extra low dispersion glasses like FPL-53 made it possible to construct f/7.5 ( doublet ) refractors again, without the use of the difficult to handle Fluorite. The triumphant decade of the f/9 ED doublets therefore soon came to an end.

Stil, even today it performs like heaven and it is nice to have a (neo)classical among my telescopes.

Sorry, I didn't back to you sooner John, unfortunately, I no longer have the 102. It was another example of me selling something I regretted later, just like a couple of motorcycles I sold in the past. Just one of those life cycles, making room for something else, something bigger. As I mentioned, I managed to network with four or five base model Vixen/Orion OTAs and all of us were on the same page as far as how good this telescope was relative to its price and specs. It was in the pre-China era and most of us know Vixen makes fine doublets anyway. I recall one memorable night looking through the 102 at Mars. What blew me away was the fact the planetary surface contrast was good enough that I could make out the darker shapes of the "continents", the northern polar region was easy to spot, maybe it was the south, I forget. I was using a 6mm eyepiece.

Soon after I sold the Vixen I fell into the rabbit hole of trying to learn astrophotography. A combination of rewards and many frustrations. I'm still plugging away tho. Thanks for the bits of historical information regarding the series. I pay attention when anyone talks about any of the Orion or Celestron Vixen telescopes. I've bought and sold maybe five telescopes since then and none of them raise any interest like the 102 still does.

Hi guys, I am super late on this one; but just a comment on the Vixen 102 f9. I had a Vixen 114ED which was stolen (long story), and I picked up a used 102 f9 as a partial replacement. It blew the 114 and my later Megrez 110 out of the water as a high power/planetary scope. Sadly I sold it along with the Megrez (not sad about that though) to help fund my TSA 102: and it even gave the Tak a run for its money. A lovely, and I think underrated scope!

- Dean

Thanks Dean for your comment!
I always wondered where the owners of the Vixen 102 f/9 were. Too busy enjoying their telescope I presume.
Luckily you and John 999R responded. I know it is a good scope, but it is always nice to hear the experience of other owners who are able to compare it to former or current scopes.

DeanD wrote: ↑Sat Aug 08, 2020 11:49 am it even gave the Tak a run for its money.

Haha, great to hear!

Very helpful article John. Thanks (though I am a bit late to the party here).