Your Ideal Scope Collection?

Post by **weixing** » Fri Mar 24, 2006 12:11 pm

Hi,

CN-212 is considered 6th best planetary telescope ever

Compare with which telescope??? Or you mean in the Takahashi telescope history??

Have a nice day.

ariefm71 · Post by **ariefm71** » Fri Mar 24, 2006 12:43 pm

Sorry, can't find the link to a review done a few years back. I remembered TEC 10" f/20 Mak (22% obstruction) came on top.

Anat, if you want planetary scope, you might want to consider an optimized 10" f/6 Zambuto newt which you can get for the price of CN-212.

Canopus Lim · Post by **Canopus Lim** » Fri Mar 24, 2006 1:13 pm

Hi Anat,

Spot diagram shows the size and shape of the spot when the telescope focus light to a point. As you know a point is not actually a point. The point is in microns and through spot diagrams people can tell what kind of aberrations (layman means error) optically the telescope has. Coma is a 3rd order aberration known as Seidal. Coma (in a spot diagram shows like a comet shape), is due to off axis (rays that are at an angle, or simply means for stars not at the centre of FOV) usually occurs for reflectors, cassegrains but it is not a real problems for achromats as they were designed to have astigmatism instead of coma. Ideally there should not be any coma in the centre of field unless the optical sytem is not collimated properly. Also the bigger the spot size with respect to the Airy disc diameter, the poorer the telescope performance. The smaller the spot size with respect to the Airy disc means more energy is transferred to the Airy disc (the centre disc you see on a focus star when at high magnification). Resolution is the ability to differentiate 2 close stars apart so hence the brighter the Airy disc (less other rings surround it), the easier to resolve (differentiate) the 2 stars. Therefore spot size diameter is a good indication of telescope performance too.

Post by **rcj** » Fri Mar 24, 2006 1:37 pm

it's Seidel....good post!

anat · Post by **anat** » Sat Mar 25, 2006 8:57 am

Canopus Lim, Thank you

Areif, do you mean Todd Gross' review?
http://www.newxspotters.net/todd/weathe ... tm#Summary

Anat

ariefm71 · Post by **ariefm71** » Sat Mar 25, 2006 10:56 am

I don't think that's the one, but looking at the top 10 planetary scope reviewed by todd gross:
- the top four are zambuto's
- the number one planetary scope is an f/4.3, very surprising for such a fast scope.

arief

elton · Post by **elton** » Sat Mar 25, 2006 12:10 pm

Actually Todd Gross' reviews are a little old ... almost 4 yrs old. I wonder if the other big dobs (starsplitter, tscopes, obsession etc) with their premium mirrors can do as well. I also wonder if SCTs have improved since. It is quite amazing that a 8" Portaball can outperform a good sample and properly cooled C-14 given the vast difference in angular resolution (granted with better contrast).

Post by **rcj** » Sat Mar 25, 2006 4:01 pm

yeah it is dated...anyway nowadays Zambutos are not at the throne of top mirror quality....don't forget RF Royce's mirrors as well....evident from high power planetary imaging with outfitted Newtonians especially those used by HK planetary imagers. A lot have changed since...however changes in SCTs might be limited though there is this XLT coating offering from Celestron and the likes...how does it really fare from Starbright coatings? Anyone did a comparison? And how about the refractors with new dispersion glasses and better coating technology.....times have changed..

ariefm71 · Post by **ariefm71** » Sat Mar 25, 2006 5:42 pm

Zambuto still top in term of consistency and resale value of his mirrors.

ariefm71 · Post by **ariefm71** » Sat Mar 25, 2006 5:45 pm

Not many people owned and tested 70+ (mostly high end) scopes as Todd Gross or Ed Ting, but here's the latest shootout I can find:
http://www.cloudynights.com/ubbthreads/ ... art/1/vc/1