Posts Made By: Roland Christen

hey, nice pic. I don't look too hung over.

Rolando

Couple of images from the Chile trip.
NGC1365 taken with Daniel's 175EDF refractor

Rolando

Las Campanas is one of about 5 observatory complexes located in a line of mountain ridges approximately 7000 ft elevation that stretches north and south in the foothills of the Andes. From the mountaintops you can see La Silla and Cerro Tololo observatories in the distance. Others are located further north in the drier Atacama desert.

Las Campanas has many telescopes, from the original 40 inch Cassegrain to the twin 6.2 meter Magellan telescope. We were fortunate to be able to visit several of the large telescopes and talk to the astronomers about their observing programs. Climbing around the catwalk of the Magellan domes and also climbing up the actual 6.2 meter telescope and examining some of the instrumentation and the huge mirror was a highlight of my trip.

Las Campanas and the other observatories located on these mountain ridges are known for their excellent seeing, at times around 0.25 arc seconds. Of course it is also extremely dark and transparent up there due to the low humidity, typically less than 10%. The attached image shows the typical seeing that we got with the 305mm Mak-Cass astrograph. It was not an especially good night according to the professional astronomers who came to see our scope's first light (being "only" 0.6 arc sec), but I would take that kind of seeing any time here in Illinois.

First light focus test of the Trapezium

Rolando

here is a center crop of the Carina nebula showing eta-Carina embedded in the tiny Humunculus nebula, which resembles a sliced tomato in H-alpha. This star is unstable and will eventually become a supernova, which will be visible in the daytime.

Rolando

Lovely result and well balanced color.

Rolando

Scope in the remote roll-off roof observatory

Rolando

Scope in the rolloff-roof observatory

Rolando

As usual you have posted some incredible images.

Rolando

The Konig is a variation of a 4 element ocular, one of many that is possible with 4 pieces of glass. Other similar performing oculars are the Orthoscopic, Plossl, Symmetrical. They all have almost totally similar performance in terms of Sidel aberrations (spherical, coma, astigmatism, field curvature, distortion), as well as color correction.

Each of them can have variations where one aberration such as off-axis astigmatism is traded for less field curvature. With 4 elements the designer has such a number of freedoms as to make almost an infinite number of different designs and give them all a different name. Those names are simply pure marketing attempts, and none of these miriad 4 element oculars has any real advantage over any other.

An example is the Plossl or Symmetrical ocular, which is easiest to make, but has the least marketing wow factor these days and has fallen out of favor. Yet it is totally undestiguishable (is that a word?) from an Orthoscopic when designed for similar performance.

Any one of these variations can be orthoscopic - the term means without distortion. This type of ocular was originally developed for microscopy where a scale was fitted at the focal plane and used to measure across a portion of the magnified images. Being without distortion meant that the scale was accurate in the center as well as the edge of the field. It does not mean that the image was free of astigmatism at the edges, so a star image is not necessarily perfectly round at that point.

Nowadays almost all oculars have compensating optics placed before the focal plane which flatten the field, remove the astigmatism of the main optics, and sometimes also increase the magnification by various amounts so as to achieve very short focal lengths using longer focal length main optics (built-in barlow magnification for short). The downside is an increase in the number of elements, along with more internal reflections and some loss of contrast - typically only seen when viewing planets.

Rolando

Those images are smooth as a baby's bottom. Great stuff!

Rolando