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Vixen VC200L for visual, tell me about it.

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#1 plyscope

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Posted 03 July 2011 - 06:09 AM

I know about the 40% obstruction. Ed Ting says it is like a nice SCT. Daniel Mounsey says it gives better (flat field sharp to the edge) visual images than your average SCT. I respect their opinions.

I like the fact that it does not have a corrector plate or a moving primary mirror. In Australia it is more expensive than a standard C8 but not as expensive as an Edge 8". It's about half the price of a Takahashi Mewlon 210. It is light weight and well made. I know it won't be as good as a Mewlon for lunar and planetary but would it be as good as a good C8? And for DSO's and using widefield 2" eyepieces I think it would be better suited. I am fortunate to have some nice refractors for lunar and planetary so this would be for compact portable aperture.

Anybody tried one?

Andy

#2 rmollise

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Posted 03 July 2011 - 07:25 AM

Yep. The same, all things considered, as a standard C8. But for more money. The focuser ain't so hot...and doesn't have much range. At least not as compared to the good, old SCT. For me: "why bother?"

#3 plyscope

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Posted 03 July 2011 - 08:16 AM

I respect your opinion too Rod. I don't mind paying a bit more for less cooling issues and less hassle with dew, better finder scope etc. So long as the performance is not worse than a C8 then I can justify the extra cost I think. :thinking:

Do you think the VC200L (VISAC) would be a little better than the less expensive VMC200 for visual?

Andy

#4 cloud_cover

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Posted 03 July 2011 - 10:15 AM

I have a VMC200L and I've brought it out for friends who have C8s. According to their comments:
-For visual, the field is flat so there is virtually no visible coma/field curvature especially with widefield eyepieces.
-It doesn't dew. Period. Its still going long after my SCT and refractor friends have packed up even without dew shield/heaters. That's a lot to say considering I live in the tropics with humidity often approaching saturation.
-Some of my friends complain their C8 has a sloppier focuser (not too sure, maybe its a sample variation thing)
- I really, really, really like the carrying handle since I also have to carry everything else:)

As an astrograph I'd say its well designed for that purpose and I really appreciate the sturdy focuser and flat field design. Even the thick spiders have become an advantage: If I forget my Bhatinov mask, all you need to do is focus the diffraction spikes until they merge from double spikes to a single slender spike (in each axis, of course)
The way I see it, if you can stomach the difference in price, the VC/VMC will be almost as good as the C8 (some reviews say the C8 is marginally brighter as it has less glass interfaces), doesn't dew up, is much better out of the box as an imager.

#5 tim53

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Posted 04 July 2011 - 01:20 PM

I have limited experience with these, but the ones I've looked through were very nice. In particular, I spent some time at a star party looking through a VMC260, and found that to be quite nice for DSOs. I don't think any planets were up to look at at the time.

I liked the views through it better than through my 9.25", and that's a good telescope.

-Tim.

#6 rmollise

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Posted 04 July 2011 - 01:37 PM

I respect your opinion too Rod. I don't mind paying a bit more for less cooling issues and less hassle with dew, better finder scope etc. So long as the performance is not worse than a C8 then I can justify the extra cost I think. :thinking:

Do you think the VC200L (VISAC) would be a little better than the less expensive VMC200 for visual?

Andy


I do, and if it just had a better focuser on it, I'd be more tempted. ;)

#7 stanislas-jean

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Posted 05 July 2011 - 04:43 AM

Hi,
I own a VC200L as second scope now.
The CO is not 40% but 42.5% actually this means a contrast level say D-d of 115mm.
Ii is used essentially for visual works on venus, uranus and mars.
Don't be afraid of the CO value, the contrast level is well compensated by the quality optics (say better than /6 P/V global).
However you have to get a perfect collimation to support these concerns, means at 360 and 450x the star pattern shall be perfect. This is easy to do with the main mirror srews.
I acquired the scope as a second hand and dismounted the tube for cleaning the optics.
The tube is open so that dusting is operant but the thermal equilibrium is quick to acquire.
The main mirror is too thin sothat when observing the star pattern of a star at the zenith with high magnifications the first diffraction ring is broken equally on 3 zones (the flexion of the mirror). But at the altitude of planets on the ecliptic the height is only 45° so that this phenomena disappears. This scope should be equipped with a 9 points cell.
The focuser seems simply but when well adjusted, shifting will be absent and focusing with an electric motor can be smooth enough.
This is a 200mm F9 that can be set to F6.4 with a corrector reductor of focus length.
Visually the FOV of 1° and little more can be reached with a 40mm 2" eyepiece.
Compared to a 203mm SCT the contrast levels are similar, the VC200l gives a full FOV without coma with pinpoints stars all FOV. The VC is less brigth than the SCT (obstruction and relectivity coefficients), heavier (6.5kgs), keeps his collimation, cools quickly.
This is a looklike RC but with a plan FOV with no significant scale deformation (for astrometry).
For DSO imaging, focusing may be a concern, but I donot have experience of imaging with.
Hope this is an help for you.
Not very used among the world but not a bad scope at final with some advantages anyway. Optics are very good (one mine).
Stanislas-Jean

#8 allan

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Posted 05 July 2011 - 06:52 AM

I have just purchased a second hand VC200L purely for astrophotography. It has a full flat field for a qhy8 camera - it was designed for 35mm film and the reducer (f6.4) also gives a full flat field. No SCT can guarantee a flat field with and without a reducer IMO, so that's why I went the vc200L. Been very happy with it and visually it seems as good if not better than the average SCT. The focuser actually is not too bad if well maintained and adjusted, so I've left mine alone - it just has an electric focuser which is quite good.

#9 Eddgie

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Posted 05 July 2011 - 08:43 AM

This scope is advertised and promoted as an astrograph.

If your primary use for it is to image, I would say by all means, get one.

For general use though, the contrast penalty is quite high. Not only is the central obstruction quite large, but there are also four rather thick spider vanes.

And it isn't particularly fast for imageing unless you use a focal reducer.

I have looked through several 40% obstructed astrographs visually and all had very poor contrast. The standard SCT is already pushing the limit of contrast loss that is tolerable, but the 40% to me is over the limit.

Also, I used to think of Vixen as having better quality than most main stream mass market vendors, but my own experience with Vixen scopes in the last 10 years has changed that opinion. I think their scopes vary in optical quality about the same as Celestron does. Some excellent, some marginal, with most being quite decent.

Here is a Vixen test on Astro-Foren.

This particular scope being tested is to me below the AVERAGE qualiity of the C8s I have owned and tested. And I have owned some EXCELLENT C8s as well. My current EdgeHD is of excellent quality.

Vixen Telescope Bench Test

So, my own advice is that if your mind is not made up or whatever objections you have to the SCT are so strong as to have you simply reject it, that you consider an SCT.

#10 Jared

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Posted 05 July 2011 - 03:01 PM

I know about the 40% obstruction. Ed Ting says it is like a nice SCT. Daniel Mounsey says it gives better (flat field sharp to the edge) visual images than your average SCT. I respect their opinions.

I like the fact that it does not have a corrector plate or a moving primary mirror. In Australia it is more expensive than a standard C8 but not as expensive as an Edge 8". It's about half the price of a Takahashi Mewlon 210. It is light weight and well made. I know it won't be as good as a Mewlon for lunar and planetary but would it be as good as a good C8? And for DSO's and using widefield 2" eyepieces I think it would be better suited. I am fortunate to have some nice refractors for lunar and planetary so this would be for compact portable aperture.

Anybody tried one?

Andy


I had one for about 18 months that I used primarily for astrophotography. Here are the pro's and con's based on my experience.

Pro's:
  • Light weight
  • Quick to reach thermal equilibrium, presumably due to the open tube
  • Fully adjustable in terms of collimation--primary, secondary, and focuser can all be independently adjusted
  • No obvious coma even at the edge of the field
  • Flat field of view (probably much more important for astrophotography than for visual use)
  • Fixed primary means no mirror flop and reduced problems with differential flexure (again, only critical for imaging and only in certain scenarios)

Cons:
  • Focuser needs to be adjusted "just right" in order to give a good experience. Note that I believe there is now an option for a two speed focuser, but it is quite pricey. The focuser does not tend to stay in perfect adjustment, either.
  • Spherical aberration was quite pronounced in my sample
  • Large central obstruction and thick spider vanes reduce contrast and produce fairly dramatic diffraction spikes. For astrophotography, these thick spider vanes tend to create diamond shaped stars rather than spherical stars.
  • Pain in the neck to collimate and requires extremely accurate collimation of all three elements in order to give best performance. On the plus side, it held collimation fairly well even when transported--perhaps a little better than your standard SCT in this regard
  • If you ever need the mirrors re-coated, you're going to have to send it back to Vixen due to the unique process of aspherizing the primary through the application of coatings--will Vixen still be around and performing this service when you need it?
  • Again, something that is critical for astrophotography only... I had huge problems with strange reflections off the corrective optics in the draw tube, and was never able to get rid of them completely. Most exposures under dark skies showed these reflections fairly prominently in all four corners of the image--almost like four separate semicircles covering the outer 30% of the corners. I don't know whether this issue was typical or not, or whether it could be addressed with some additional baffling or flocking.
  • Can't figure out why Vixen still isn't using compression rings in their focusers. They should drop the flip mirror diagonal and use the money they save to put in compression rings. Not a big deal, obviously, but they just aren't meeting "table stakes" in this one area--as far as I know on any of their scopes.

Overall, I found the scope to be a decent astrograph. It covered my (then current) 35mm CCD chip and was flat to the corners or very nearly so. That is really good, and fairly rare even on scopes marketed as astrographs. The reflections were a real pain, though.

I simply wouldn't recommend the scope for visual use. The contrast loss from the large secondary and thick vanes was obvious, and the mediocre spherical correction on my sample further degraded performance.

If you were looking for a mid-priced 8" astrograph of moderate focal length it's probably a pretty good deal. If you just want 8" of portable aperture for visual use, I would look at a different design. An SCT would probably be a better choice unless you are really excited by the idea of an open tube design with no mirror flop.

#11 plyscope

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Posted 05 July 2011 - 06:42 PM

Thank you everyone for the detailed responses. It does give me a clearer idea of what to expect and though it seems like a good scope I don't think I would be satisfied in the long run. I have never tried imaging and have no intentions to. I enjoy my refractors up to 6" for visual observations and am looking at going up in aperture in the future. It looks like a Mewlon 210 or other cassegrain more suited to visual is going to be my best option. Otherwise I will have to accept the compromises of an newtonian or 8" achromat.

Andy

#12 stanislas-jean

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Posted 06 July 2011 - 01:13 AM

I think about the quality images they are quite depending of the alignment and collimation level of the OTA.
These points are crucial to be performed perfectly.
As said above the scope was dismounted for cleaning and I re-assess the alignment for re-assembly. This is sharp to be aimed and crucial for quality level. A slight misalignment involves a great effect in degradation.
I think most of the bad reports could come from this point.
Returning on the contrast levels having observed long times on long period the comparison for me is done. The VC200L exhibits the sligth contrasted features on venus and uranus that a sct cannot do. In spite of the great CO present on the VC200L. There are reasons for these results, mainly 2 the alignment and the quality of the optics.
Visually this an excellent scope if very well aligned only.
See for exemples the following links
http://alpo-j.asahik...10/v100715z.htm
http://alpo-j.asahik...10/u100920z.htm
You may find some others with various scopes from me.
These results come from the fact that at the ultimate resolution area for the scope, the contrast level is higher with high CO, especially for the no CO scope (as a refractor).
The degradation in contrast due to the CO effect occurs mainly at medium resolution rates (see the FTM curves for reference).
Stanislas-Jean


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