Re: [tec-scopes] Best planetary telescope?


Dec 18, 2002

 


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#864 Dec 18, 2002

I would like the groups opinion on which telescope would be best for

high power work on planets, the Moon, and possibly the Sun. The 12"

TEC Mak, or a 16-20" f/4.5-5 Newtonian with tracking and a thin

quality mirror with cooling fans (Zambuto, Royce, Spooner,..)?



The larger aperture of the newtonian will of course give a higher

theoretical resolving power and more contrast and colors on the

planets. On the other hand, the fast focal ratio means collimation is

critical, and the diffraction limited field of view is small. Is

depth of focus an issue? With the newtonian heat from the observer

may cross the light path. And as Markus Ludes recently claimed, open

tubes may give a slightly less stable image than closed tubes.



I am the type who is willing to wait for the short moments of really

good seeing, and at the moment I live in a place with periodically

quite good seeing. Which of these telescopes would give me the best

image of the planets? Is the 12" TEC likely to perform better during

average seeing than a larger newtonian properly cooled and collimated?



Jon Kristoffersen

home.no.net/jonbent/astropages.html



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#866 Dec 18, 2002

--- In tec-scopes@yahoogroups.com, "jon_bent jon_bent@h...>"

jon_bent@h...> wrote: > The larger aperture of the newtonian will of course give a higher

> theoretical resolving power and more contrast and colors on the

> planets. On the other hand, the fast focal ratio means collimation

is > critical, and the diffraction limited field of view is small. Is

> depth of focus an issue? With the newtonian heat from the observer

> may cross the light path. And as Markus Ludes recently claimed, open

> tubes may give a slightly less stable image than closed tubes.

>

> I am the type who is willing to wait for the short moments of really

> good seeing, and at the moment I live in a place with periodically

> quite good seeing. Which of these telescopes would give me the best

> image of the planets? Is the 12" TEC likely to perform better during

> average seeing than a larger newtonian properly cooled and

collimated? >

> Jon Kristoffersen



Hi Jon,

I will poit just on a few issues:



1. Focusing

1.1. Defocusing:

MAK at f/15 has defocusing range about 200mk

Newton at f/4-f/4.5 has 16-18mk, - about 10 times shorter

1.2 Focusing range

MAK has appr. 8" that is fine for many accessories including

binoviewers, filter wheel, etc.,

Newton has much shorter focusing range



2. Diffraction limited field

In 12" f/15 it is about 30 mm dia. (no coma)

In Newton at given ratio it is only in the center



3. Resolution:

12" vs. 20" - you know the answer.

I saw easy the Enke division in 20" Zambuto at WSP 2000, but had no

chance to see it with our 12" MAK yet.



All other issues are your choice.

regards, Yuri



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#868 Dec 18, 2002

Jon,



As an owner of a 20" f/4.25 Zambuto mirror Dob and a 10" f/14.6 Mak-Cass, my

experiences with planetary observing for the last 3 years with these two

scopes is that my 10" Mak has been more useful with planetary observing more

times than the my 20" Dob has. This was due to the higher percentage of

seeing that supported my 10" Mak and probably wouldn't have added any better

viewing with the 20" Dob those very same nights. I don't take both scopes

out to test side-by-side. The only times I would bring out my 20" to a dark

site would be to spend more time with deep sky instead of any planetary

observing. Some nights with the 20" did support larger ap. planetary viewing

at high powers with a bino, but the 10" Mak probably would of been well

served also on those nights, also. One thing for sure--my larger ap. Dob did

show fuzzy planetary views on half the nights I observed with it due to the

fair or poor seeing. The deep sky observing saved the night on during those

nights of mediocre seeing. The only thing that's guaranteed with a larger

ap. Dob--the planetary image will be brighter no matter how crisp it looks.

During times of very good seeing, this has allowed me to see more planetary

shading, fainter moons, subtle detail over neighboring smaller ap. scopes.



Peter Natscher

Monterey, California


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