Celestron Onynx 80 EDF

[timthelder]

Has anyone read any reviews or tried this little scope?...

http://www.celestron.com/c2/product.php?CatID=60&ProdID=396

Just curious, the specs make it sound like it might make a good little piece of equipment.

[omaroo]

Sounds like a lot of money for an 80mm achromat. The WO 80ED is around US$530 - a whole lot cheaper. Are they comparable?

What is "Fluorite based, low dispersion glass"? I though fluorite was a crystal formation - i.e. it had to be grown.

[Radar]

G'day Tim,

Haven't looked through one, but for that price, and with Celestron's name on it, it will more than likely be a good little scope. Though the points Chris has raised are worth investigating more.

How long has this been on the market for, does anyone know? I couldn't find a decent a review anywhere. :confused:

Cheers

Ray

[timthelder]

I found this short review on it which sheds a little more light...

http://www.cloudynights.com/ubbthreads/showthreaded.php/Cat/0/Number/1359489/page/0/view/collapsed/sb/5/o/all/vc/1

And in the January issue of Astronomy Magazine there is a write up on it, but I don't have that issue.

Astronomics gives a pretty good description as well. Base price is $699.

From what I gather, this is another spin-off of the Orion express 80, same lens configuration,(one FLP-53 lens, with a crown glass lens) only without the XLT coatings. Antares also has one of this type, and WO has the Zenithstar.

Seems to be the "in" thing to combine the two lens's, one for color correction, and the other to achieve the short focal length...

Anyway, thanks for the input. Much obliged.

[Radar]

So Tim does this scope come as an APO?

[timthelder]

So Tim does this scope come as an APO?


No, not fully,
The way I seem to be understanding these descriptions, is this...For a scope to be considered 'apochramatic', any or all lenses must be color corrective ED glass, FPL-53, 51, etc.

Otherwise, manufacturer's cannot advertise their product as being an APO...Hence the new term Semi-APO. A mid-level scope that has the best of both worlds, color correction, and an affordable price.

I did find these'uns here that are pretty interesting...

http://01f35a7.netsolstores.com/refractors.aspx

Amazing how many scopes are out there that 'look' like other scopes.

[omaroo]

And then there's calcium fluorite crystal....

Here's an interesting page (sorry about the reference to Takahashi):


Takahashi fluorite lens

Apochromatic means “free from spurious color” – a refractor system without the faint violet halos of out-of-focus light you see around the planets, the limb of the Moon, and all the bright stars in an ordinary achromatic (crown and flint glass) refractor. All Takahashi fluorite doublet optical tubes are true apochromatic optical systems, with virtually perfect color correction.

Takahashi has been the acknowledged leader in ultra-premium apochromatic fluorite optics ever since they produced the first commercial fluorite refractor in 1979. That system moved Takahashi to a position of industry leadership in terms of optical quality, and Takahashi has never looked back since moving to the head of the class.

The Takahashi two-element air-spaced objective lenses use a full aperture laboratory-grown calcium fluorite crystal lens element, combined with a high refractive index flint-type glass element. This yields very high color fidelity and vanishingly low levels of spurious color. Laboratory-grown fluorite crystals are used, rather than naturally-occurring crystals, due to the lab-grown variety’s optical uniformity, clarity, freedom from striae and internal stresses, freedom from being adversely affected by dew and moisture (as early natural-crystal fluorite lenses could be), and their ability to be hard multicoated in a vacuum chamber for high light transmission.

The Takahashi color correction equals, or exceeds, that of most triplet lens systems regardless of cost or brand name. Contrast is generally superior to triplet systems or doublet systems that use a low-dispersion crown glass element instead of fluorite crystal.

Since the Takahashi two-element air-spaced designs have fewer light-absorbing lenses than triplet systems, they have less glass to absorb light, therefore yielding brighter images than triplets. All optics are fully ion-deposited hard multicoated (including the fluorite element) for maximum light transmission and contrast. In addition, light loss is about 0.5% at each multicoated lens surface in an air-spaced system, versus about 2% at each oil-spaced surface. Maintenance is less than oil-spaced designs, since there is no oil to potentially leak or become cloudy with age. In addition, Takahashi lens cells are fully collimatable for peak optical performance by using a simple optional Cheshire-type collimating eyepiece and the locking collimating screws on the lens cell.

The diagram below shows the differences in color correction between a conventional BK7 optical glass lens (shown in red), an ED glass lens (in blue), and a lens of calcium fluorite crystal (in green). The smaller the departure from the ideal focus, shown by the vertical line labeled “0”, the lower the amount of chromatic aberration and the better the correction for the specific color shown at the left of the diagram. You’ll note that the green line of the fluorite lens shows much less chromatic aberration across the entire visible spectrum than either of the other two glass types.

http://www.astronomics.com/main/fsdiagramf1.jpg

Source: http://www.astronomics.com/main/description_expand.asp/expand/d2SNAV9A2R3ST9PDNRV/pproduct_id/FS60/pcategory_name/CUJ52QSW9PGJ9MTQ2QU8593HR1/pcatalog_name/Astronomics

[CanisMajorTom]

so a doublet is better than a triplet. interesting.

[Tenacious Del]

so a doublet is better than a triplet. interesting.

i'm still trying to get my head around this. :crazy: