Posts Made By: Roland Christen

Looks like an old Volvo or Saab.

Rolando

The major cost in refractor or any other telescope system is the labor going into the grinding and polishing of the optical elements. While ED glass is not cheap, it is not the most expensive part of the production process.

One can make a very cheap achromat lens using two common glass elements by CNC grinding and fast machine polishing of the 4 surfaces. This does not get you a precision result. If you want 1/10 wave accuracy of the central green wavelength you really need an accomplished optician to do this step, which results in high cost. Since achromats don't have very good color correction to begin with, one does not need to tweek the radii to an exacting level according to each melt batch, so an achro can be made more cheaply overall.

However, when you are trying to achieve the highest level of spherical and color correction, regardless of the use of ED or diffraction elements, the labor of making it to a high level of performance is the dominant cost driver, not the glass cost.

I can see one advantage in this scheme: you can make bigger lenses above 10 inches with available glass. ED glass is not readily available in those sizes.
However, there is a point of no return in lenses that large. Years ago I brought a 10" Mak-Cass with 23% central obstruction to the Winter Star Party, set up right next to a massive 10" Triplet Apo from Lzos, Russia. Believe me, the Mak-Cass was sharper, more contrasty and had less coloration than the Triplet. The acid test was separating Sirius B from the brilliant light of Sirius, and the Mak-Cass did that far better than its lensed cousin. At the time, Sirus B was a mere 4 arc seconds from the primary. Plus the Mak-Cass weighed a fraction of the refractor and fit easily into the trunk of my compact car.

Rolando

Ford out of the '50's

Darren Drake said:

WOAH!

http://www.astronomics.com/main/product.asp/catalog_name/Astronomics/category_name/SHVWMWFRC43G9LK595R250JH90/product_id/ES12009

Before you celebrate too much, here's a bit of sobering fact:

Congress sat idle in Washington as China lured U.S. manufacturers to their mainland, stole our discoveries and inventions, and trained their students in America's elite universities.

According to the U.S. International Trade Administration (ITA), in 1989 American total imports of Chinese manufactured goods was about $12 billion; by 2000 it rose to over $100 billion; and by 2010 it had skyrocketed to $365 billion.

Conversely, the U.S. exported to China a mere $5.8 billion in manufactured goods in 1989, for a net trade balance of $6.2 billion in China's favor. By 2000 China's trade lead over the U.S. expanded to $83.8 billion; and by 2010 it had exploded to $273.1 billion.

They use our local airport for training flights too. See them about once a month here.

Rolando

Woah! That is one huge picture! Impressive to say the least.

Rolando

P.S. for the noise in the faintest areas, you might look into Topaz, which is a Photoshop smoothing plugin. You can get it from this link: http://www.topazlabs.com/denoise/

There are lots of different kinds of coatings that can adhere to a glass surface, and we cannot assume that each can be easily removed.

For example, the coating of a mirror sits on the surface of the glass and is made of metal that can be etched off. Therefore such a coating can be removed easily without using mechanical means.

The coating of a lens is partially embedded in the glass surface, and is made up of oxides and fluorides, that are similar in composition to glass. They are highly resistant to chemicals and acids, and even if they could be removed this way, they would take part of the glass with them. Therefore the only way to remove them is by polishing. This of course changes the figure of the glass and the lens would have to be refigured, which is a time consuming costly operation.

On the other hand, a coating such as produced by a fingerprint (or roast beef vapor in your kitchen) does not have to be polished off or removed via acid etching, and can be removed easily with simple soap and or alcohol/acetone wiping. A roast beef coating is easy to apply and to remove, whereas an anti-reflection coating is not so easy.

Rolando

David Kernberger said:

Can anybody tell me what the letters A S P on my oldish B & L 30 mm focal length eyepiece might mean? It is 1 1/4" diameter and is not a Huygenian (sp?) type, as it will focus an image on an an external surface. The image quality , when used in a telescope, appears to be just so-so. It also has at least some form of anti-reflection coating.

Thanks,
Dave K.

Plossls are made with two achromats back to back. They can be two different achomat lenses with the eye lens smaller than the field lens, or they can be two achros of the same design and even of the same diameter. It makes almost no difference to the on-axis or off-axis performance. There are advantages in cost and manufacturing for each of the above styles.

A classical Orthoscopic normally consists of a triplet field lens and singlet eye lens. Orthoscopic means that the field has no displacement distortion and thus a scale can be placed at the field stop and the divisions of the scale will look idential everywhere in the field.

Both Plossls and Orthos are inherently othoscopic and have very similar off-axis performance - both have off-axis astigmatism when designed for a flat field. They can be designed to have anywhere from 30 degree to 50 degree apparent fields with good supression of astigmatism and field curvature depending on the scope's focal ratio.

Generally the design should be matched to the focal ratio of the telescope that they are being used with in order to get the most performance. The longer the focal ratio, the larger can be the apparent field. Generic Plossls and Orthos are designed with some middling f-ratio in mind and will work best with F8 or longer scopes.

Rolando

is the eye relief it provides dependent in any way on either the focal length of the objective or the focal ratio of the objective?

No.

Spectacular!
especially the higher res image.
Rolando