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Anyone know the lamba of the Vixen VC200L? (lamba/4?)

NickK

By NickK
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NickK

NickK

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Just out of interest I've been attempting to track down the lamba value for the Vixen VC200L but can't find an answer anywhere! I'm assuming it'll be lamba/4. 1800mm fl, f9 or 6.4 with reducer.

I know the standard Orion Optics OMC200 is lamba/4, the deluxe is lamba/6 and I'd have thought with a customised cost that they'd do lamba/10. 4000mm fl means f20.. stunning detail but hideously long exposure times.

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ollypenrice

ollypenrice

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Just out of interest I've been attempting to track down the lamba value for the Vixen VC200L but can't find an answer anywhere! I'm assuming it'll be lamba/4. 1800mm fl, f9 or 6.4 with reducer.

I know the standard Orion Optics OMC200 is lamba/4, the deluxe is lamba/6 and I'd have thought with a customised cost that they'd do lamba/10. 4000mm fl means f20.. stunning detail but hideously long exposure times.

The big issue with the VC200L is the thick spider vanes so even if you get a nice tight star you get a big thick cross through it! However, some images have appeared recently which show a fabulous improvement when the vanes are machined down. I don't know if you have seen these results?

Olly

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NickK

NickK

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The big issue with the VC200L is the thick spider vanes so even if you get a nice tight star you get a big thick cross through it! However, some images have appeared recently which show a fabulous improvement when the vanes are machined down. I don't know if you have seen these results?

Yup, I've seen the results from thinning the vanes and they're quite impressive. It certainly shows the VC is no optical slouch for the money.

Ahh OO is an ex-importer of Vixen, now I can see the connection and rivalry with the VC an OMC being very similar (including the photos using a sphinx mount!).

I'll shoot OO an email and report back.

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NickK

NickK

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"Unfortunately we cannot guarantee to achieve 1/10PV on an OMC200 as there are too many variables involved, especially the thick piece of BK7 glass. 1/8 PV is achievable but 1/10 is not."

I'm assuming that the small size of the lenses (compared to 12+") makes the process too prone to error and thus makes it unviable for them commercially.

They've, understandably, refused to comment on the Vixen lambda value.

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narrowbandpaul

narrowbandpaul

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lambda means wavelength.

The value you are actually after is the PV (Peak-Valley) wavefront error expressed as a fraction of the wavelength used to conduct the test...usually a 632nm HeNe laser.

I would expect Lambda/4. That is usually the minimum quality you will see in amateur scopes.

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riklaunim

riklaunim

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There was some problems with those Vixen VMC/VC OTAs - You can see that after some fixes the strechl ratio went up. It's very easy for a catadioptric scope to go bad by misalignment or similar problems. The same was with GSO RC. Tests gave bad results... but it did work superb when imaging at night. After some changes - tests started looking more correct.

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pete_gamby

pete_gamby

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Out of curiosity, I asked Vixen Japan to comment on this thread and I thought I'd share the response:

"We do not open criteria of our factory inspection for lenses and mirrors used for Vixen telescopes, but we would like you to understand that excellence of optics must be verified by means of a telescope in which a complete optical train is incorporated.

We do not put ourselves on a standpoint where people only talk about advertised optical performance of primary mirrors. Also we don't know how right their measurements are. Vixen is proud to inspect finished telescopes severely, not just a component of them to deliver products of the first grade in optical performance to our consumers."

They also pointed me to the following link:

Accuracy - What Does it Mean?

Cheers, Pete

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TheTalescopeMan

TheTalescopeMan

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I don't have a VC200L, but I did very recently buy a VMC200L from Optique Unterlinden whilst they were having a stock clearance sale. (For £690 including delivery :)). So far I have been very impressed with the quality of the view that the 'scope gives and feel that the characteristics of the design probably have more influence on the views available than whether the main mirror is lambda/4 or lambda/5 or whatever.

Firstly, it seems to hold collimation very well. I have used it as it came out of the box from the factory and when I did a star test it looked just about ideal. With a 2" diagonal and 38mm 70degree eyepiece the field of view is very respectable at almost 1.4 degrees without any vignetting. Despite the substantial vanes, the diffraction spikes are, to my eye, not that intrusive and only really noticeable on the brighter stars. I wanted a compact scope with good aperture that was suitable for deep-sky observing and it certainly seems to deliver here.

Seeing conditions have not been ideal here in the last few days, with quite a bit of late mist around, but the scope really seems to take high magnifications well when observing the moon. I took it up to 486x and the image was still really sharp, allowing me to look in detail at the cliffs and so forth around individual craters.

Only weak spot seems to be planetary observation. Perhaps it will perform better in clearer conditions, but I haven't got significantly more detail out of Jupiter than I do with my Tal-1, with the image being rather 'soft'. This could be related to the relatively large central obstruction, but then again this allows relatively wide-field views with a 2" eyepiece, which is more important to me. (This could also be partly due to Jupiter being quite low when I was observing it, and from my viewing point it is now moving towards the lights from a big city).

The VC200L probably shares some of the above characteristics, but it of course has a parabolic primary mirror, rather than the spherical one of the VMC200L. I have read in the Vixen literature that the parabola on the mirror of the VC200L is created by a special aluminum vacuum evaporation technique, which is supposed to give a more accurate mirror than traditional polishing. If this means that the mirror is better than the one on my VMC200L, then it will be good! Only downside is that the main mirror will have to be returned to the factory if it ever needs re-coating, as the glass itself is figured to a spherical surface.

I hope some of the above is useful!

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ollypenrice

ollypenrice

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I always feel on these threads that you can drown in the technicalities. However, if you look at the images taken you have some idea of what you might really produce. For me the VC200L is pretty good once that spider is hacked about, but otherwise it doesn't appeal because, in the dense starfields in which I often image, the small stars are disfigured by the thick vanes. Galaxy hunting outside the Milky Way you might feel differently. Oh for the perfect telescope!

Olly

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NickK

NickK

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Oh for the perfect telescope!

I was reading an interesting article on PVs too that draw doubt over the metric. How you measure, what you measure and the change in the measurements over wavelengths can't be summed up in a non-formally defined standardised value of 1/4.

I agree Olly. It's the reason I have my temperamental manual spring-loaded lever coffee machine - the resulting espresso.

I'm still yet to settle on a specific form and I'll switch between lunar to deep space (as much as I can see with my current setup!). Given the gravity of feeling about the spider on the web (:)), it very likely that Vixen know about this. I'm not going to postulate on Vixen's motives for not addressing the issue, other than suggest that the larger scopes in the range probably don't suffer the same issue.

The jury is still out about my mount+scope purchase - but that's a different thread!

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narrowbandpaul

narrowbandpaul

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these wishy washy statements like 'it looks good' and 'it gives nice views' are just a load of subjective ****.

the only way to tell whether the optics are good is to measure the surface accuracy of the mirror. In practice the seeing will smear out details and you become seeing limited rather than diffraction limited.

your definition of good and someone else's will differ. Therefore no fair comparison can be made unless you test the mirrors.

there are far too many subjective opinion based reviews out there, which really needs to end. The same applies for reviews of cameras. I recall a review by martin pugh of the STX. His review was one of the worst I have seen, and when you try to challenge him on it he makes wild accusations for which he offers no apologies. Reviews need to be based on hard numbers that dont lie!!!

paul

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ollypenrice

ollypenrice

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these wishy washy statements like 'it looks good' and 'it gives nice views' are just a load of subjective ****.

paul

Paul, I'm not sure I can accept this in all circumstances. Most people here are amateur astronomers wanting to take attractive pictures of the night sky.

It is, I would suggest, perfectly 'scientific' in this context to look at pictures taken with a certain telescope and say, 'is that what I call attractive?' If it isn't, it isn't and that is, in this context, a hard fact.

I don't like images taken with standard VC200Ls. I think that they often look awful. You can measure the resolution till you are blue in the face, and the spot size, and the even-ness of illumination, but what I see is an image with mis-shapen little diamonds for stars and ugly thick diffraction spikes and it does not meet my house standard. I'm not a scientist at the camera, I am a (not very good!) artist.

So I agree that telescope reviews waffling on about diamonds on black velvet or M42 looking very nice at 42x are neither use nor ornament but a subjective view of a resulting image (one's own subjective view) is very valid for one's self.

If this was not the thrust of your point then my apologies. As you know, I am a great admirer of your posts.

Olly

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John

John

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...there are far too many subjective opinion based reviews out there, which really needs to end.... l

If this did end Paul, there would be virtually no reviews of equipment ever posted here or on any any other amateur forums. Do you really want that result ?

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NickK

NickK

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I'd like to think of myself as a scientist - probably due to having two physics teachers as parents - but I find myself following feeling rather than logic.

To be honest, the spikes wouldn't cause me as much of a problem if the resulting reward allowed me to look deeper into the subject (both imaging and visual) and explore. I can see that the scientifically better optics will allow me to delve deeper and notice the nuances - the scientist in me - whereas I can look at a large image and think 'yes' which is governed purely by feeling and emotion.. the artistic side doesn't mind. I tend to be infuriating because I flip between them at will and anger both scientists and artists!

Although I opted for a Pentax 105SDP, the longer focal length still intrigues me for the ability to get into the subject and explore. Only thing is a long focal length, low f is a large aperture and we're into Peter Shah's OO 12" or 14" rather than the VC200L. The OO 12" has minor spikes but look at that detail!

All said.. that little vixen newt is quite nice :glasses1:

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ollypenrice

ollypenrice

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We all want at least a dozen different focal lengths and we all want them at f1.8!

What's wrong with that? Pass me the cheque book, my sweet...

Yes, compromise, compromise, but let's not complain. Would you have believed, in 1998, that the images posted here were by amateurs with small telescopes? One thing I am sure of though; when you get that Pentax aimed at the sky you are not going to wish for anything else for a while...

Olly

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