On Thursday, January 12, 2017 at 6:40:21 AM UTC-5, Martin Brown wrote:
On 06/01/2017 11:42, wrote:
On Friday, January 6, 2017 at 5:21:56 AM UTC-5, Martin Brown wrote:
On 05/01/2017 21:03, wrote:
On Thursday, January 5, 2017 at 3:23:48 PM UTC-5, Martin Brown wrote:
On 05/01/2017 11:13, wrote:
On Wednesday, January 4, 2017 at 12:34:25 PM UTC-5, Martin Brown wrote:

It is a more polite term for a light bucket. A bit more effort having
gone into optimising it for wide field views usually at the expense of
on axis sharpness in all but the premium models.

For planets, I would go for the 12-inch f/5 Newt over the 5-inch f/12 refractor. YMMV.

Depends a lot on whether the 12" f5 Newt mirror has a turned down edge.
Many cheap light buckets have less than stellar performance at higher
magnifications when they were only designed for use as RFTs deep sky.
Stopping it down a bit will improve the image quality no end but won't
fix the lamentable collimation errors that they also tend to have.

You are making a strawman argument, at best.

ROFL You know that what I say is true but won't admit it.

No, what you say is a gross mis-characterization of short focus reflectors, ie a strawman.

Yeah! Right! Lets just do the math.

300mm @ f5 fl = 1.5m

Light cone at furthest possible secondary position 30mm + 48mm = 78mm to
fully illuminate a typical 2" wide field deep sky eyepiece.

Even without the ubiquitous turned down edge so typical of a never mind
the quality feel the width light bucket mirror intended mainly for deep
sky observation to match the wide field requirement of a 2" focuser the
secondary obstruction is over 25% on a 12". That is way more than is
acceptable for seeing low contrast fine planetary belt detail.

But don't take my word for it:

http://www.brayebrookobservatory.org...m/c-o%27s.html

and certainly not
when the seeing and systematic errors in the optical surfaces prevent
the effective use of high magnification anyway.

Again, a strawman.

Using a webcam and registax the seeing at least can be eliminated but
there is nothing much can be done about intrinsic systematic errors.

And another strawman.

Anything you disagree with you simply dismiss as a strawman.

Last one I looked through which ISTR was a 14" f5 mirror that appeared
to have been silicone or maybe PU glued onto a crude 18mm plywood base.
Collimation was a joke. The Galilean satellites looked like seagulls
flying round a blob with only the north and south equatorial belts
actually visible. It was easily outclassed by a 4" refractor or an 8"
SCT both present. The refractor sometimes showing an Airy disk on stars.

It did a lot better on faint fuzzies but the very poor collimation still
meant that stars were not exactly round even at low magnification.


You seem to forget that -I- never mentioned "mirrors glued to plywood" and that -I- get to decide details about the telescope, the mirror and the manner in which those are assembled, managed, used and adjusted.

Quit making strawman arguments, brown.