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Vixen NEO140 'achromat' Question

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#26 jrbarnett

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Posted 13 October 2013 - 10:19 PM

That's part of the plan.

The other piece of the plan is to pair it up with the C9.25 Edge HD and my CGE mount as my travel ensemble. Both are flat. One goes deep but is narrow. One less deep but wide. Neither is crazy expensive, either.

- Jim

#27 Dave Lee

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Posted 14 October 2013 - 09:23 AM

Well, folks. I just bit the bullet and bought on ebay a Vixen NA140SS described as four years old and never been used. Reputable seller but I guess you never know. At $1k it was too good to pass up.

This discussion (and others) has convinced me that I will probably end up with a couple of refractors before I end up with 'the one' (or maybe 'the none'). However this seemed like a scope (if it is as described) where I can recover my investment.

This is the a very good scope for one of my stated interests (better star images and background contrast vs. a C11) but somewhat less than optimum for my other stated interest (double stars). But hardly a terrible choice.

Plus this scope should have the minor advantage of being better balanced than the typical refractor (rear lens elements) as I have a permanent pier/G11 in my back yard and don't currently have an easy way to raise the head.

I'll report back when I have first light. I am a star hopper and am really looking forward to star hopping through a primary objective!! And maybe some day I will buy a dual saddle for my G11 and use both scopes at the same time.

Thanks again for everyone's input.

dave

#28 fred1871

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Posted 14 October 2013 - 06:04 PM

All the best with the new scope, Dave. I hope it's a good copy of the model. If it is, I suspect you'll find it better for double stars than you expect. I did, so I use it much more often for doubles than my C9.25.

#29 Dave Lee

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Posted 14 October 2013 - 07:11 PM

All the best with the new scope, Dave. I hope it's a good copy of the model. If it is, I suspect you'll find it better for double stars than you expect. I did, so I use it much more often for doubles than my C9.25.


Tonight someone will probably offer a Televue NP127is for $200 or something. Oh well :lol:

dave

#30 seeindoubles

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Posted 14 October 2013 - 11:01 PM


Tonight someone will probably offer a Televue NP127is for $200 or something. Oh well :lol:

dave [/quote]

Mine! All Mine! :jump:

#31 Doug Reilly

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Posted 16 October 2013 - 10:01 AM

The SSf models were assembled, or at least quality controlled, in Japan. The objective lenses were made in China. I just had to replace my front objective lens in my NA140 (don't ask, I don't want to talk about it) and I had the option of getting either a Chinese-made example mrstarguy had on hand from a demo unit, or a new Japanese made objective at significantly higher cost, including shipping the ota to Japan. I was told that the new NA140 model will be going back to these japanese-made lenses. I am assuming that the optical design will be the same since they were offering the new Japanese glass as a swap in, unless they intended to replace both lens sets in the OTA....could be. Anyway, there is a new all Japanese NA140 on the way.

I really enjoy my NA140, enough to replace the front objective! (At least i bought the original chipped at ridiculously low price so now i an up to what a good used one would cost, and I think it is still worth it. Not quite the deal of the century that it was. Interestingly the new cell is in better collimation than the one it replaced. There is variation.

I have though about how to add colliamation provision to the scope, something akin to Televue's crude but effective bolts for adjusting tilt. I now have an empty cell to play with, and a friend with a machine shop....

#32 Dave Lee

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Posted 19 October 2013 - 04:21 PM

Well, folks. I just bit the bullet and bought on ebay a Vixen NA140SS described as four years old and never been used. Reputable seller but I guess you never know. At $1k it was too good to pass up.

snip

dave


Had kind of a 'first light' today. Scope arrived so I set it up for some daylight viewing. Keep in mind here that, while I have a decent level of DSO viewing experience from back in the 80's/90's, my high mag experience is thin and refractor experience (other than a couple hours with a 6" APO 25 years ago) is nil.

The scope as represented was 4'ish years old and unused. I took that with a grain of salt (but with the expectation of very good condition). However, if the seller had told me that this was a brand new scope being drop shipped from Vixen, I would have believed that. It even had the original "plastic wrapper" around the OTA. This thing is cosmetically pristine showroom condition.

FWIW, this is a very heavy duty focuser. VERY much so. The tension knob is really nice to have (and works well) and the fine movement is going to be very important, I think. Again, most of my experience is DSO work with an 8" and 11" SCT so I don't have a good comparison base here.

Unfortunately it is cloudy now with little chance of that changing tonight. So the best that I could do was to aim at a tree branch maybe 75 yards away. And note that this was a day of full, but not really heavy, cloud cover.

The purple haze becomes obvious at 80x. I didn't buy an apo so was hardly surprised here. Next I just banged it up to 312x (2.5x power mate and 6.4mm plossl). The purple haze was not exactly worse (maybe a little). And clearly the image was darker. But finding focus was simple (thanks to the fine focus feature) and the image seemed to hold up well. If the goal had been to describe the features of the brown branch to as great a level of detail as possible, I'd probably have chosen that magnification (even at a less than 0.5mm exit pupil). BTW, there was pretty much no cool down time here but the indoor and outdoor temps were within 7 degrees or so. Of course that purple haze is visual information that is being lost - no way around that.

Two other pieces of good news.

1) My existing "14 inch SCT Telegizmo 365 cover" works fine on this scope. If the forecast is good I'll leave the scope out a few days.

2) Using my 56mm plossl EP (max 2" FOV) is quite comfortable. My plan here is to do star hopping through the main tube (no finder) and that EP will give me a better than 3* FOV (and an exit pupil that is WAY too big). This will save me the trouble of mounting a finder (I hope) and will allow me to move a better 32mm EP well down the priority list.

Will post more when I know more.

dave

ps. Eddgie (and others) may well be right that the best operating point for me might be a 120-130mm ED level scope. But I think that I can recover close to my expense if I decide to move on, so I am giving this a try.

#33 russell23

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Posted 19 October 2013 - 04:49 PM

Dave,

If you don't like the performance above 100x for your observing objectives I would suggest again that you consider the Baader 495 longpass filter. I was testing a new Barlow two days ago in daylight. I was at 120x with the Baader 495 filter on my diagonal with my Vixen 140NA and there was not a trace of CA on trees, branches or anything else I used as a test target - exactly what I have seen on the Moon, Jupiter, Vega, Altair ... That filter is a true fringe killer!

Dave

#34 Dave Lee

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Posted 19 October 2013 - 07:29 PM

Dave,

If you don't like the performance above 100x for your observing objectives I would suggest again that you consider the Baader 495 longpass filter. I was testing a new Barlow two days ago in daylight. I was at 120x with the Baader 495 filter on my diagonal with my Vixen 140NA and there was not a trace of CA on trees, branches or anything else I used as a test target - exactly what I have seen on the Moon, Jupiter, Vega, Altair ... That filter is a true fringe killer!

Dave


Dave, I will definitely be trying out your suggestion of a Long Pass 495 filter (quite inexpensive) as well as the Badder Fringe Killer (or something similar).

When I think about this issue in the context of what I just observed (tree branch with a fringe), I see (and/or expect) the following 'errors'

1) The obvious fringing. If I were to imagine a goal of seeing the detail on the branch as well as is possible, this seems to me to be a (relatively) trivial issue for the most part.

2) There must be improperly focused light spread about the target itself (inside the fringe boundaries) which smears out the image a bit.

3) Light that should have been focused properly is now 'gone' which must (to some extent) reduce the quality of the image.

It would seem to me that a proper filter can 'go after' #1 and #2, but not #3. Of course if you could go after all three of these issues effectively, you'd be seeing a lot fewer APO's and a lot more achromats.

dave

#35 Dave Lee

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Posted 21 October 2013 - 06:58 PM

Had the new scope (Vixen NeoAchromat 140mm) out last night. I didn't have a ton of time here, but here are my first impressions (again keep in mind that my high mag experience is thin). The night had mostly clear skies (wispy cirrus clouds moving around randomly), 98% illuminated moon, rapidly dropping temps, and seeing that varied widely.

I spent a fair amount of my 2 hours getting accustomed to the scope and how I would use it for star hopping. I had hoped to avoid a finder scope (use a 56mm plossl in primary optical path for star hopping), just line up the tube instead of a Telrad/etc., etc. No finder is going to work just fine, I think (despite the 10mm exit pupil), but I may end up with a Telrad or equivalent.

I always have trouble when manually moving a scope on a GEM. My (non-Gemini) G11 'pushes' just fine, but I always seem to have trouble trying to find 'pure RA movement' vs. 'pure DEC movement'. My C11 has this neat little handle on the bottom/rear that is perpendicular to DEC motion. Took a while to orient myself here (this problem seems to be unique to me, BTW).

Once I got the movement (and scope balance) straightened out I decided to just turn my back to the moon and start on something familiar (the double-double, Epison Lyra). I had set the scope up a good 2 hours earlier, but had noticed that the OTA was REALLY cold to the touch (I assume that it was that OTA radiating to a dark sky). Images were literally boiling around. I'll swear that at 200x I saw the orientation of one of the double-double pairs flip 90 degrees!

So I just put the 56mm plossl on and did some experimental star-hopping to nowhere in particular. Things seemed to settle down fairly quickly, so back to the double-double.

The pair was 'suspiciously elongated' at 80x and well split at 120x. I have viewed this in my C11 a couple of times and things just looked a bit more crisp in the Vixen vs. the C11. And I don't recall an obvious split at less than 200x in the C11. I would not claim a night and day difference here, but it was real and not subtle. I did bump the magnification up to 312x, but the seeing really didn't support that magnification.

Since I was in the area I dialed in The Ring Nebula. It was detectable in the 56mm plossl (14X and 10 mm exit pupil, basically full moon). Structure (or at least a 'ringness' was detectable (with great effort) at 120x but things began to kind of wash out at higher magnifications.

I then moved to a couple of easy doubles (Beta/Zeta Lyra) and they were easy and very pleasant views.

Now for my general impressions.

1) I believe that I am really going to enjoy star-hopping at 140mm/f5.7. Despite having a better than typical finder on my C11 (Lumicon 80mm finder), I really somehow liked moving around through the main OTA (with around 3* FOV).

2) The scope fits fine on my existing permanent pier (designed to hold a C11). I was worried about the height, but it is fine.

3) Things do seem to be sharper in the Neo (vs. the C11). I would not claim a night and day difference, but it is real. Sky darkness is hard to judge under a full moon.

4) This thing has a nice focuser (said the guy who has only extensively used the focusers on SCT's).

5) Vega begins to show unwanted color at around 80x. Bigtime at 120x. I encountered no other color issues (not the moon comment in the ps).

6) The Televue Powermate (2.5x) seems to be a really good 'Barlow' from this limited experiment.

7) This one surprised me (a bunch). I found myself wondering if better eyepieces would be helpful. I have a kind of hodgepodge of a couple of ES 82* models, a couple old Meade plossl's, a couple of old UO's, and an ancient Orion Erfle. The answer to this question is far less interesting to me than the fact that it was a question in the first place. It had simply never occured to me before. Have no idea what to think of that.

That's it.

dave

ps. My plan was to look at the moon at the end of the session. At that point the moon had darted behind some high cirrus, so I called it an evening.

#36 seeindoubles

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Posted 21 October 2013 - 08:45 PM

Better eyepieces will help. When I first bought my 140 and later my AT152, I used what I had. The best of the lot at the time were some run of the mill generic Plossls and the best were some old Celestron Ortho's. Later on, Teleview had a "sale" and I splurged and bought three eyepieces, a 10mm Radian, a 5mm Radian and a 19mm Panoptic. Man, do I love that Panoptic! It quickly has become my favorite eyepiece in my still fairly limited selection. The Radians are great for splitting doubles and planetary but I love the Panoptic as a "relatively" affordable eyepiece for looking at nebula, sweeping star fields. Both the 140 and the AT152 yielded nice views though I never really got to fully test the 140. I have also used all three eyepieces with my current Celestron C150R refractor and have been very happy with the views through the Panoptic. It also works very well with my C11.

#37 Dave Lee

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Posted 22 October 2013 - 10:40 AM

Unfortunately, now that I have experienced a 3+* FOV through 140mm of aperture (albeit with a 10mm exit pupil), a really good 30'ish mm widefield EP is also now on my list. Oh well.

dave

#38 russell23

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Posted 22 October 2013 - 11:36 AM

Unfortunately, now that I have experienced a 3+* FOV through 140mm of aperture (albeit with a 10mm exit pupil), a really good 30'ish mm widefield EP is also now on my list. Oh well.

dave


The 28mm ES68 works very well with the Vixen140 NA.

Dave

#39 t.r.

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Posted 22 October 2013 - 11:40 AM

Unfortunately, now that I have experienced a 3+* FOV through 140mm of aperture (albeit with a 10mm exit pupil), a really good 30'ish mm widefield EP is also now on my list. Oh well.

dave


"Ignorance is Bliss"...But now you know. :grin:

#40 ohioalfa64

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Posted 02 November 2013 - 03:30 PM

When considering purchasing filters for the Vixen 140ssf, I am looking at the semi-APO or the mentioned here 495 long pass filter. Any suggestions on which is better for viewing Jupiter at a high magnification?

#41 russell23

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Posted 02 November 2013 - 08:13 PM

When considering purchasing filters for the Vixen 140ssf, I am looking at the semi-APO or the mentioned here 495 long pass filter. Any suggestions on which is better for viewing Jupiter at a high magnification?


The 495 Longpass completely cuts CA. The semi APO does not because it is just the Fringe Killer with the M&SG. I have had far better results with the 495 Longpass on Jupiter than with the Fringe Killer.

Dave

#42 ohioalfa64

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Posted 14 November 2013 - 07:44 PM

In this section in the blog regarding CA filters, it is stated that you need a 140mm APO to outperform this Vixen Neo for visual use. Without restarting this issue, is that the accepted opinion here, using the 495 Longpass filter on bright objects?

#43 russell23

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Posted 14 November 2013 - 08:50 PM

In this section in the blog regarding CA filters, it is stated that you need a 140mm APO to outperform this Vixen Neo for visual use. Without restarting this issue, is that the accepted opinion here, using the 495 Longpass filter on bright objects?


No, it is probably not the accepted view. Let me clarify to hopefully stem a tide of overreacting uproar. What I said is that if the Vixen 140NA with a Baader 495 Longpass provides 15-20% less light than a 140mm APO - then in order to have an APO that provides noticeably more light than the filtered Vixen 140, you probably will need at least a 140mm APO.

The cautions are:

1. If you can afford an APO in the 127mm to 140mm range there is a good chance that you will find the overall view of the APO superior because APO's are typically manufactured to a better figure than achro's.

2. APO's retain the full range of visible wavelengths whereas the filtered achro is restricted to 500-700nm wavelengths.

What the Baader 495 Longpass does do is significantly sharpen an Achro to the point where in my comparison with my 80mm ED APO it appears as sharp as the APO for deep sky and lunar observations.

Since the 120mm ED APO's are actually cheaper right now than a Vixen 140 NA the 120mm ED would probably be a better choice between those two if you are looking for something larger than the 100mm scopes.

But the larger 6" f/6 achromats are still lower cost than the 120mm ED and a lot lower cost than a 140-150mm ED so if deep sky is the primary objective and you want a refractor you might be better off with the filtered 6" achro at that point.

But maybe not.

My main point in all this is that the Baader 495 Longpass significantly sharpens and cleans up the views with an achromat.

Dave

#44 Saied Mabrouk

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Posted 15 November 2013 - 01:29 AM

Two years ago, I did ask Vixen USA what is the focal ratio of the front achro doublet of their Neo 140. They contacted Vixen Japan and the answer came that the focal ratio is 8.42 (F/8.42)and the second achro doublet is F/17.3 (and contributes little CA). That is why it has less CA than 6" F/8 achro, but more CA than 5" F/8 achro.
If the front achro doublet is F/12, the second doublet would be of larger diameter and faster (lower focal ratio) to keep the length of the scope manageable, and the large diameter second achro doublet would introduce additional CA.
Regards.

#45 Rich

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Posted 15 November 2013 - 01:49 AM

Interesting info Saied. The typical Petzval design is roughly 2:1 as has been mentioned, but I'm not too surprised the design could be different. Roland C. has described the Petzval as having more CA than the long primary, but less than the overall focal ratio would suggest, which sounds like it matches with what Vixen told you. Less CA than an F5.7, but still a moderate amount.

My experience with the Vixen NA 120 (F 6.7) shows low false color but still easily appearant. At 120 F 6.7 it should be substantially less than the 140. Cool scopes I've always thought. Sharp, wide field, and flat.

#46 Dave Lee

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Posted 15 November 2013 - 07:27 AM

Two years ago, I did ask Vixen USA what is the focal ratio of the front achro doublet of their Neo 140. They contacted Vixen Japan and the answer came that the focal ratio is 8.42 (F/8.42)and the second achro doublet is F/17.3 (and contributes little CA). That is why it has less CA than 6" F/8 achro, but more CA than 5" F/8 achro.
If the front achro doublet is F/12, the second doublet would be of larger diameter and faster (lower focal ratio) to keep the length of the scope manageable, and the large diameter second achro doublet would introduce additional CA.
Regards.


Thanks so much for the definitive answer to this question.

I was looking at Jupiter (through a NEO140) the other evening (briefly - it was quite low in the sky) and at 180x there was no EASILY detectable color fringing. OTOH, but the Baader 495 LP and Baader Fringe Killer seemed to SLIGHTLY increase contrast (really only detectable if you held the filter and moved it in/out of the exit pupil). For those situations I would have chosen the Fringe Killer as the 495 gave things a definite yellow tinge that the FK mostly did not.

But clearly there was some CA of significance going on or the two filters wouldn't have been helpful. The view was mostly limited (in this case) to the excess atmosphere (very low viewing angle).

dave

#47 Eddgie

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Posted 15 November 2013 - 09:26 AM

Anyone that has ever read about polychromatic strehl in an acromat can tell you that no filter will allow an acromat like this to rival an APO.

There are two different issues with CA. The first is that you see color. That is actually the smaller of the issues with an Achromat. I call it a cosmetic error.

Far more serious is the energy that is removed from the Airy Disk of a star, and likewise from inside the border of all details on an extended target and spread into the neighboring details.

On a star, this will have the effect of lowering the encircled energy. The Airy Disk of the star will be reduced in intensity in much the same way that a secondary obstruction removed intensity from the Airy disk, though where the energy goes is completly different.

The end result is the same though.. The star will have reduced intensity against the background and the instrument will have less limiting magnitude performance than the APO.

For details on extended targets, all but black details will have energy moved from within the border of the detail and laid over the neighboring detail. This is the same thing that Spherical Aberration or a central obstruction do. They both take energy either from the Airy Disk or the inside the broders of a small detail and overlay that energy on to neighboring detais, lowering contrast for all details present.

Once again, this energy is being taken from where it would be in the APO and put elsewhere.

And no amount of filtering can restore this energy to where it would go in the APO. The energy that is spread against the background may be filtered out, but the lower intensity of the Airy Disk and the lower energy of a brighter detail on a darker background is not restored.

You can read about Polychromatic Strehl here.

Figure 73 has many graphs that will explain how the dilution of the energy intensity affect the performacne of the instrument.

Affects of energy intensity loss (polychormatic strehl) on point and extended...

So, not sying that you may not improve the appearance of the view. If you find the color annoying, you can filter it away.

But a filter cannot restore the enegy into the borders of the detail on an extended object from which the enefgy has been removed, lowering the contrast the same was a central obstruction does, and it cannot restore the energy into the Airy Disk of a star.

Read about CA on the link above and you will quickly relize that the damage is done, and a filter can't really make a 140mm achromate compete with a 140mm APO. You simply suppress color, but don't move energy back to where it would be in the perfect instrument.

Or easier yet, find someone with a TEC 140 and filter up.

Filters remove energy. They do not have the ablilty to re-focus it. Look at the PSF intensity plots for an achromat in the figure on the link above and you will quickly see the problem.

Oh, by all means, get the filter if the CA annoys you. I am sure you will find the view more satisfying.

And for extended objects, the filter can actaully improve the contrast ratio against the background, but it lowers the brighness along the way, so that is kind of a wash, but maybe for some very faint targets it might make the difference between seeing and not seeing the target.






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