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Vixen NEO140 'achromat' Question

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#1 Dave Lee

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Posted 12 October 2013 - 09:15 AM

I may someday add a refractor to my currently C11/G11 dominated arsenal. The NEO140 is on my (very long) short list. I have two questions about this scope.

1) From a visual CA perspective is this thing basically a 140mm f8.5 (rougly) achromat. Or does the Pertzval lens also do something helpful with CA? My CA concerns are less the infamous 'halo effect' and more about the 'visual information' that is lost on dimmer objects at high mag (like double stars).

2) Can the objective be collimated? In doing some research I ran into multiple instances of collimation issues (out of the box) but it was not clear about how (if at all) this could be fixed by the user.

Thanks.

dave

#2 Eddgie

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Posted 12 October 2013 - 11:05 AM

The instrument uses an achromatic lens with a focal ratio of around f/11 or f/12, so the color correction is only as good as a similarly large f/11 or f/12 achromat, and of course even an f/12 achomat at 140mm is far short of what you could achieve with a 140m ED glass.

Still, as compared to a 6" f/8 telescope, the improvement is quite obvious.

The rear elements are esentially a built in focal reducer which convert the light cone to f/5.7, but the color is not improved as a result of this lens. Some of it though could have been the result of being an achromat.

When you take energy out of the Airy Disk, it really doesn't matter where it goes (filtered or scattered over a very wide area to dilute it), the net is that you have less energey and in an achromat it is less powerfully concentrated.

I found that on stars, ED scopes seemed to be able to come very close to slightly larger achromats in presenting the faintest stars. While the total system tranmission may stil be better with only M2FG coatings, you are still simply not concentrating the energey nearly as intensly as with an ED or APO. For bigger differences in apeture, it des not matter, but when the difference is small, I think the delta in performance is a bit smaller than one would think.

Both leneses are mounting with no provision for collimation, but I have owned two and both were in excelletnt collimation. IF though it were to come in uncollimated, it would require shims to correct. There really isn't much way for them to loos collimation though. The rear doublet is mounted onto a tube that threads directly into the end of the focuser housing so even denting the tube will not throw it off.

The front is mounted in a very sturdy cell and only tube damage could change it (assuming that it was originally shipped in perfect collimation).

I did not think the light transmission was quite as good as the aperture would have indicated. Closer to a 5" apeture than a 6". I do not think that the entire system was multicoated at the time. More likely single MGf2 on the lens surfaces.

I love the wide field views that it gave because the field was very flat and offered pinpoint stars out to the edge with modern wide fields.

Unless you need something this fast though (people do image with them in B/W), these days, I personally might lean to a 120ED.

But I enjoyed mine for what it was while I had it...

Picture shows the four refractors I had at the time...

Left to right they are a Meade 152ED.. I liked this scope better than the Vixen for everything but wide field. The image was quite a bit brighter and the contrast was very high vs the Vixen.

6" f/8 achromat. Bought from Overseas and while posessing high quality otpcs, I did have some problem with the scope, and once again, I was much happier with the performacne of the Meade 152 ED. This was a western european made lens highly optimised for gree ligth so it was nto an issue of quality. The Meade simply being an ED I think gave it better performacne. Nothing to do with fringing, but everything to do with how much more easily it was to see planetery detail in the 152ED.

Vixen 140. As you can see, not much smaller than the 6" f/8 achromat, but not much bigger than the last scope, which is a Vixen 102 (Orion version).

Now keep in mind that a don't fine all that much value in small apeture refractors, but of these four, I found the 152ED easily the most satisfying to use for things that would fit into the field of view.

And based on my experience with a huge number of achromats and all kinds of filters, these days, I would recommend a smaller ED or APO scope over any kind of larger achromat.

But smaller means only slightly smaller. I would rather have the Vixen 140 over the Vixen 102 or a 102mm APO. I personally just find 4" scopes to be far to limited unless you are willing to travle to very dark skies.

Just my opinion... Nothing more.

But as you can see, I owned all four of these at the same time and spent many nights comparing the views.

I did not own a 120ED, but based on these four and the other half dozen refractors I have owned (most of which failed to amuse me for very long), I would lean to the 120ED for a general use instrument especially considering that the price is similar.

The Vixen though would be the best of these for low power, wide field viewing. It easily offered the widest true field, and it was coma free and very flat. For low power viewing only, I might still go to this scope.

For general use though, I would these days lean to the 120ED types.

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#3 Eddgie

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Posted 12 October 2013 - 11:12 AM

Just a followup. If they are now fully multicoating the lenses, this could change my opinion a bit. Again, I felt that the image was a bit dimmer than the 140mm apeture woudl have suggested. I would ask Vixen if they have stepped up and started using super-high transmission coatings.

If not, then it is still questionable as to whether this scope will be as bright as a similar sized moderen doublet with highest transmissin coatings.

If on the other hand, they have improved the coatings considerably, maybe it would be more acceptable.

But you still have a lot of energy that is not going into the Airy Disk. Coatings don't fix that. Filters don't fix that, and nothing else fixes that except moving to ED glasses or triplet lenses. Don't expect the limiting magnitude to be quite the same as a 140mm APO. It is just the light robbing that happens with an achomat, and in a 140mm f/12 achrmoat, this is not an insignificent amount. Takeing the energy out of the Airy Disk and fattening the ramaining energy concentraion will just make it impossible for the achromat to match a triplet in limiting magnitude.

Again, just my opinion.

#4 Dave Lee

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Posted 12 October 2013 - 11:56 AM

Eddgie, thanks so much for the very rich and informative reply(s).

dave

#5 Eddgie

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Posted 12 October 2013 - 12:22 PM

My pleasure.

I would love to be able to say "Get the Vixen 140... I had one and I loved it," because I did have one and I did love it.

But larger apeture ED scopes today make the value proposisiton for less compelling.

I would rather have a Vixen 140 than a 6" f/8 achromat (I owned three of those... Two Celetron CR150s and the imported model pictured above, and I enjoyed the 140NA more than any of these bceause these were to me only really fun at lower powers.

But this is now, and when you can get medium apeture doublet ED scopes for what is essentially about the same price or a little more, it really changes my opinion now that we are in the second decade of the 21st Century.

I hope you get other opinions. Mine is only one opinion, and in a perfect world, you would get opinions from someone that has owned the 140 and compared it to several other instruments as well.

One opinion on CN is just a fly smushed on the windshield of life.

Of course, the consensus opinion on CN is like a lot of flies smushed on the windshield of life.

If you can get feedback from some other owners that have compared it to slightly larger and slightly smaller apetures though, I think you would get a more complete picture.

Good luck with your decision making. The truth is out there, and a credit card will get it for you.. LOL.

#6 jrcrilly

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Posted 12 October 2013 - 12:54 PM

One opinion on CN is just a fly smushed on the windshield of life.

Of course, the consensus opinion on CN is like a lot of flies smushed on the windshield of life.


That's a great expression of the contrast!

I liked my NA140. It was nicer in every way than the 6" F/8 doublet achromats I owned, both the Synta and the JOC versions. It wasn't nearly as good an imaging platform as the more expensive 6" F/9 Meade barely-ED doublet, though. A modern ED doublet with higher-Abbe number ED glass could be better yet - but probably more pricy.

I'd still give the NA a lot of points for widefield visual use. Great build quality and nice views.

#7 Jim Curry

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Posted 12 October 2013 - 05:46 PM

I have one and love it. Built like a tank, if this gets out of collimation you have other issues to deal with, like backing the truck off it first. How faint can you go with this? I've found a dozen or more galaxy's fainter than 13 with this. The flat field of the Petzval design means you don't need exotic eyepieces to enjoy it. In fact I sold my Ethoi because they were inducing a warped view. On a still night I had rock solid views of Jupiter to over 250x. A halo yes but detail galore in the belts. The Veil in a 31 Nagler is all there, Pickering too.

I have one about 5 years old with Japanese glass, I've read that the newer OTA's have Chinese sourced glass with a different quality of image.

Jim

#8 fred1871

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Posted 12 October 2013 - 07:34 PM

I've also got the NEO 140 - had it 5 years, bought new, "made in Japan" on the sticker. The optics appear to be multi-coated and the light transmission is very good for the aperture - mag 13 stars from the suburbs on moonless nights, no problem.

It's built solidly, and I can't see it having collimation issues.

Eddgie's review(s) of it were part of making up my mind to get the NEO 140. I'm glad I did. Great for wide-field due to the flat-field Petzval design, it proved extremely good for high-power observing as well. 400x is no problem for the closest double stars when the atmosphere allows high power.

Chromatic aberration? - sure, but as others have said, less than your typical 6" f/8 achromat. Only obvious on the brightest objects, such as Jupiter; but you can use filters (something us older-generation planetary observers did anyway) and the detail is very good.

Works well on deep-sky stuff too - better than I'd expected on globular clusters for showing stars in them, shows detail on some planetary nebulae (eg the Eskimo in Gemini), great on open clusters. I'd say it performs every bit as well as the very good 6" f/8 Newtonian I used to have, and does better on some things such as doubles. And it doesn't have collimation needs and is less affected by temperature issues.

Not a choice for imaging (get an apo); but for visual it's an excellent choice.

#9 seeindoubles

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Posted 13 October 2013 - 01:47 AM

I also bought my NA140 based in part by Edggies excellent review of the OTA. I had also ordered an Astrotelescopes 152 and received it at about the same time. I never got to use the Vixen under dark skies, only from light polluted skies in Beaverton, Oregon. I did get to use the 152 at my backyard observatory in Lapine, OR and was so impressed with both the light gathering ability and quality of images that I made the hasty decision to sell the Vixen. I now regret that decision since I wish I had taken more time to test it under dark skies. When I did get to use the 140, I found the images to be first rate. It split all my favorite doubles well, with crisp well defined airy disks in good seeing. I did note that it took a pretty short focal length eyepiece to get the magnification required. That meant less eye relief which took away from the experience. As was stated by others, the 140 is probably better suited to lower power, wide field views of deep sky objects, clusters, etc. I probably woud buy another one someday, provided I could get a deal. New, ,they are too much money compared to some of the new high end larger achromats or 100 to 120mm ED scopes out there for similar expense.

All this said, if you are lucky enough to own one of the Vixen Neo-Achro 140's do go out of your way to enjoy it under dark skies and avoid the mistake I made in letting mine go.

#10 russell23

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Posted 13 October 2013 - 06:58 AM

I love mine but to get the best out of it you really need to use a CA reducing filter. The scope has nice flat field views and eyepieces play nicely with it. The CA reduces contrast and makes it difficult to get pinpoint sharp stars - especially at higher magnifications.. I've tested this many times. Pick a group of stars and a magnification of 100x or greater. Try to focus on the stars and you will find that it is hard to find sharpest focus and when you do the stars seem slightly blurred. Then pop on a Fringe Killer or #8 light yellow filter, refocus, and those stars will be pinpoints and the field will be cleaner.

I've recently discovered the Baader 495 longpass filter which seemingly turns my Vixen 140 into an APO. There is zero purple fringe. I''ve noticed certain stars are actually double, triple, and quadruple stars that I never noticed before. I'm using my Vixen 140 at full aperture on the Moon and getting sharper views than when I was using a 107mm aperture mask with the Fringe Killer.

So yes, I love my Vixen 140, but only because of the use of CA reducing filters. If you are into double stars a filter will be a necessity.

Dave

#11 t.r.

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Posted 13 October 2013 - 07:43 AM

Dave, I've been following your filter thread...how does Jupiter look in this scope with the 495 longpass filter? Do you get used to the strong yellow? I can just tolerate the #8. But if this long pass actually does something extra or different than the other filters, it may be worth the investment.

#12 Dave Lee

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Posted 13 October 2013 - 07:50 AM

I love mine but to get the best out of it you really need to use a CA reducing filter. The scope has nice flat field views and eyepieces play nicely with it. The CA reduces contrast and makes it difficult to get pinpoint sharp stars - especially at higher magnifications.. I've tested this many times. Pick a group of stars and a magnification of 100x or greater. Try to focus on the stars and you will find that it is hard to find sharpest focus and when you do the stars seem slightly blurred. Then pop on a Fringe Killer or #8 light yellow filter, refocus, and those stars will be pinpoints and the field will be cleaner.

I've recently discovered the Baader 495 longpass filter which seemingly turns my Vixen 140 into an APO. There is zero purple fringe. I''ve noticed certain stars are actually double, triple, and quadruple stars that I never noticed before. I'm using my Vixen 140 at full aperture on the Moon and getting sharper views than when I was using a 107mm aperture mask with the Fringe Killer.

So yes, I love my Vixen 140, but only because of the use of CA reducing filters. If you are into double stars a filter will be a necessity.

Dave


Dave, a VERY insightful and useful post - thanks.

I wonder (regarding double stars) what the difference would be between a whatever filter and just stopping down the NEO to (for example) 4 inches which would yield (from a CA perspective) an achromat at f17.

Just a thought. Thanks again for the perspective.

dave

#13 russell23

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Posted 13 October 2013 - 08:12 AM

Dave, I've been following your filter thread...how does Jupiter look in this scope with the 495 longpass filter? Do you get used to the strong yellow? I can just tolerate the #8. But if this long pass actually does something extra or different than the other filters, it may be worth the investment.


I find myself rapidly getting used to the yellow. On the Moon last night I noticed it was yellow but the "wow - that sure is yellow" reaction from the first night was gone. Jupiter looked yellow yesterday morning but I was so engagaged by how sharp the views were. It was the first time ever where I felt like the Vixen 140 was being limited for planetary views by the seeing rather than the scope itself.

Normally I use aperture masks and the FK with the Vixen 140. I've found that a 78mm aperture mask I made with the FK seems to give essentially CA free views on Jupiter. But using that aperture mask limits resolution and floaters start appearing sooner.

With the 495 Longpass filter I had the Vixen 140 at 200x on Jupiter and it was sharper than it usually looks with my 107mm Aperture mask at ~120x. I might actually do some sustained planetary observations now that I have this filter. Normally I slap on the aperture mask and FK filter, take a quick look and say to myself "Yep - this scope still stinks for planetary observations if I push it above 100x" and go back to star clusters, galaxies, and nebula. So I was very pleased to be able to be at 200x and have both the seeing and the scope accomodate the magnification yesterday morning.

Now I know planetary observers are very discriminating and I won't go so far as to say that I project this filter makes the Vixen 140 as good as an APO for that purpose, but the 495 Longpass is actually making me think about doing some planetary observing when the planets are up.

As for the yellow color on Jupiter - I didn't mind, but I imagine it is not as pleasing to the eye as an unfiltered true APO.

Dave

#14 russell23

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Posted 13 October 2013 - 08:18 AM

I love mine but to get the best out of it you really need to use a CA reducing filter. The scope has nice flat field views and eyepieces play nicely with it. The CA reduces contrast and makes it difficult to get pinpoint sharp stars - especially at higher magnifications.. I've tested this many times. Pick a group of stars and a magnification of 100x or greater. Try to focus on the stars and you will find that it is hard to find sharpest focus and when you do the stars seem slightly blurred. Then pop on a Fringe Killer or #8 light yellow filter, refocus, and those stars will be pinpoints and the field will be cleaner.

I've recently discovered the Baader 495 longpass filter which seemingly turns my Vixen 140 into an APO. There is zero purple fringe. I''ve noticed certain stars are actually double, triple, and quadruple stars that I never noticed before. I'm using my Vixen 140 at full aperture on the Moon and getting sharper views than when I was using a 107mm aperture mask with the Fringe Killer.

So yes, I love my Vixen 140, but only because of the use of CA reducing filters. If you are into double stars a filter will be a necessity.

Dave


Dave, a VERY insightful and useful post - thanks.

I wonder (regarding double stars) what the difference would be between a whatever filter and just stopping down the NEO to (for example) 4 inches which would yield (from a CA perspective) an achromat at f17.

Just a thought. Thanks again for the perspective.

dave


Dave,

I've done this. The main aperture mask I use is 107mm which makes the scope an f/7.5 but for color correction it is much better than that. I thought I read that the objective of the Vixen 140 is an f/8.4 but Ed was saying it is an F/12 so now I'm not sure. But there is no doubt if you use an aperture mask you improve the color correction and if you combine that with the Fringe Killer you can get views that are almost CA free and are very sharp. Before getting the 495 Longpass filters the best views I had of Jupiter were with the 78mm aperture mask and the FK filter at ~120x. It was very sharp and free from CA.

The nice thing is that when you have the 140mm aperture it is easy to play around with aperture masks, but you can still go big if you want to.

Dave

#15 t.r.

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Posted 13 October 2013 - 08:23 AM

Dave, FYI...when I had my TEC140 on the best nights I could run 245x on Jupiter. At 200x, you're there for our average NY skies!!! That's doing pretty well. ;)

#16 Jim Curry

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Posted 13 October 2013 - 09:51 AM

F ratio wise the Petzval design is nominally a 1:2 scope. The scope is rated at f/5.7 so the native fl of the objective is around f/11 and will have color correction of an f/11 140 achromat. Stopping the aperture down to X influences the f/ll ratio.

Jim

#17 Eddgie

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Posted 13 October 2013 - 01:16 PM

If you have not done so, you may want to look at the currently running thread where someone compared a 6" achromat to a 5" ED scope.

It will I think re-enforce my suggestion that you may do as well with a modern 120mm ED scope.

#18 russell23

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Posted 13 October 2013 - 02:15 PM

F ratio wise the Petzval design is nominally a 1:2 scope. The scope is rated at f/5.7 so the native fl of the objective is around f/11 and will have color correction of an f/11 140 achromat. Stopping the aperture down to X influences the f/ll ratio.

Jim


Ok, so the Vixen 140 then would be an F/11.4 objective? So I've been remembering that incorrectly and thinking it was an F/8.4.

Dave

#19 Dave Lee

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Posted 13 October 2013 - 02:30 PM

Eddgie, I have been following that thread with some interest.

The more that I read/study/learn here the more that I am convinced that the 'right answer' is not an answer but a journey. The idea is that I am going to have to experience a variety of scopes in this class to figure out which is best for me. So the most efficient implementation of such a journey is to find reasonable deals on used 'reasonable choices' so that I can recover most of my investment if/when I decide to try something else.

The optimum plan would be to set aside the capital to always own two scopes of this class, 'trading in' the least desirable for 'something else' until you feel that you are unlikely to do better.

Or something like that :-)

dave

#20 fred1871

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Posted 13 October 2013 - 05:49 PM

Given the moderate level of CA in the Vixen 140, I'd think f/11.4 a likely figure.

The comments above from Dave (russell23) suggest to me that these scopes might vary a bit as well as different observers seeing differently. Mine has been very good on double stars with no filter; the Fringe-Killer does improve star images, but in my case it doesn't need as much improvement as Dave has found. Unfiltered, I've used it regularly at 285x and 400x on close doubles with sharp images. Neat figure-8 "kissing" doubles at Dawes Limit (0.83"); elongation visible on closer near-equal pairs down to my current record of ~0.5" (several examples).

Likewise, for planets - Jupiter is fine in mine at 133x and 160x, unfiltered; better with the FK, or the Baader Contrast Booster, or the Semi-Apo; or coloured filters to show narrower waveband images. But at that aperture (140mm) the best effect will be at middling magnification, same as with a Newtonian; so no benefit on Jupiter above 200x-230x.

Mars takes magnification better, and less filtration needed. 230x and 285x were useful some nights.

I've never felt the desire to stop the scope down, tried it; less light, less resolution, and merely a reduction in CA on the bright objects. Filters with full aperture worked better.

The short focal length does mean short eyepieces - but if you're not restricted to Plossls, that needn't be an eye relief problem. Nagler T6 (12mm er) go down to 2.5mm; Pentax XW and various others, with 20mm er, are available to 3.5mm. When I want high powers I often use a TV Powermate 2.5x - 2000mm effective focal length, no discernable loss of image quality, and 400x with a 5mm eyepiece that can have 20mm er.

Eddgie suggests a 120mm ED instead - I'd agree that for some people that would be the better choice. But I went with the Vixen 140 and don't regret it; I've had time observing with a good 120mm ED, very nice, but I'll stay with the 140 - a bit more light and resolution. And the CA can be easily worked around.

In the past I've had some telescopes I regretted buying, but this isn't one of them. It's not as wonderful as a couple of AstroPhysics refractors I've used long-term, but it was hugely more affordable, and in my country the Skywatcher 120 ED costs more than the Vixen 140.

The nice thing these days is having a lot of options available.

#21 Dave Lee

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Posted 13 October 2013 - 06:16 PM

A related question. Am I correct that when I encounter a used NEO140 model that the 'SS' model was built in Japan and the SSf model was built in China (for better or worse).

Thanks.

dave

#22 Eddgie

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Posted 13 October 2013 - 06:29 PM

From my first post to you on this topic:

The truth is out there, and a credit card will get it for you.. LOL.


It may take several transactions.. That was implied.

LOL.

#23 fred1871

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Posted 13 October 2013 - 07:20 PM

A related question. Am I correct that when I encounter a used NEO140 model that the 'SS' model was built in Japan and the SSf model was built in China (for better or worse).

Thanks.

dave


Mine has 'SSf' on the same label that says 'made in Japan'.

#24 jrbarnett

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Posted 13 October 2013 - 09:38 PM

I've been enjoying the Astrotelescopes 152mm f/5.9 achromat for quite some time now. I think I'll sell it and try one of the latest crop of Vixen NA140s as an alternative.

- Jim

#25 russell23

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Posted 13 October 2013 - 10:06 PM

I've been enjoying the Astrotelescopes 152mm f/5.9 achromat for quite some time now. I think I'll sell it and try one of the latest crop of Vixen NA140s as an alternative.

- Jim


Jim,

If you do or even if you don't get the Vixen 140, you should pick up the Baader 495 Longpass filter and see how it improves the sharpness of views provided by the achromat. I know you have or had a TEC 140. It certainly would be interesting to do a comparison between the TEC 140 and the Vixen 140 with the 495 longpass since some people seem to think the value (or lack of value) of a large achro comes from its inability to match an equal aperture APO.

Dave






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