A telescope test page

Hi, I found a webpage that describe the difference in telescopes when
we looking at Jupiter, I wonder if anyone could tell me if those
images are close to what we wil see if we look trough the telescopes
that they have used in this "test".

http://www.dnsolutions.at/binoviewer...bberator7.html

It looks like the 114mm/900 reflector have a sharper image of Jupiter
comparing to the 120mm refractor.

The page are on German but the exampel are easy to understand.


Tim.

Hi, I found a webpage that describe the difference in telescopes when
we looking at Jupiter, I wonder if anyone could tell me if those
images are close to what we wil see if we look trough the telescopes
that they have used in this "test".

It depends on conditions as well as the quality of the optics. It looks to me
like they have chosen optimal conditions.

It looks like the 114mm/900 reflector have a sharper image of Jupiter
comparing to the 120mm refractor.


Most 114mm reflectors have spherical mirrors rather than parabolic mirrors as
they should... Wonder which the simulation used.

There is a program called Aberrator which is free and can be downloaded at:

http://aberrator.astronomy.net/

I imagine that was the program that was used for the simulation but you can do
it yourself...

jon

"Tim" wrote in message
om...
Hi, I found a webpage that describe the difference in telescopes when
we looking at Jupiter, I wonder if anyone could tell me if those
images are close to what we wil see if we look trough the telescopes
that they have used in this "test".

http://www.dnsolutions.at/binoviewer...bberator7.html

It looks like the 114mm/900 reflector have a sharper image of Jupiter
comparing to the 120mm refractor.

The page are on German but the exampel are easy to understand.
The problem is that there are a lot more 'variables', than simple focal
length, aperture, and reflector/refractor. Given good seeing conditions,
and reasonably 'cheap' instruments, what they are showing is probably
right. The refractor is showing a noticeable amount of chromatic
aberration (which is why there is the red/purple 'fringing' to the image,
which is what is degrading the fine detail). This gets worse with 'faster'
focal ratios (which is why the 120/600 refractor shows it even more). This
is curable, but at a cost. Designs referred to as "APO's", use a different
glass, showing much lower dispersion, in a combination to bring the
chromatic aberration down to levels that require even higher magnification
than shown, to be visible (technically reducing it to zero, at three
points in the visible spectrum, and correcting spherical aberration at two
points as well). For a given aperture these will beat the reflector, _but_
cost massively more. Remember also there are other 'compound' scopes than
the SCT that they show. The Maksutov-Cassegrain, is particularly suited to
planetary observation, giving high focal lengths (and therefore
magnification), in a small package.
If you are comparing a reflector and refractor at similar price points,
the difference is probably about right, though a filter could be used
(with care), to remove the ends of the visible spectrum, and massively
decrease the amount of CA seen, and improve the image from the refractor.
The images appear better than will be seen, except on that odd occasion of
superb viewing, or as a result of using large numbers of images, and
computer processing to bring out the best detail.

Best Wishes