[ATM] A nearly perfect image from a set of 127mm diameter F/5 ratioL-H telescope lens

["Ukyo Chen" <ukyochen888@hotmail.com>]

Dear all,

I am in a project now.

------------If you already know well about Lurie-Houghton you can jump to 
next page-----------------
You can hardly find another middle or short focus telescope which will 
perform wonderful image, easy to assemble and get low price other than L-H 
type.

We only talk about middle or short focus telescopes here. Because even long 
focus L-H or Newtonian will get better quality, their tube will be too long 
to carry compare with Cassegrain type.

What’s the shortage of traditional refractor?
1.	Achromatic refractor still has much chromatic as bad as spherical 
aberration and coma etc. Very terrible image.
2.	Achromatic refractor using ED material will get better, but still 
visible, still big spherical aberration, coma and so on. Also it is not 
cheap.
3.	APO refractor will reduce chromatic to very low level, unfortunately 
purple light still spread out the focus. Also spherical aberration, coma and 
other aberrations not fully recovered. And it cost too much!

Then how about the reflector and catadioptric?
4.	A parabolic Newtonian reflector doesn’t have chromatic, perfect in the 
image center, but the coma becomes huge,  stars away from the center turn 
into comet now. Parabolic surface is not easy to make, if you make a 
spherical mirror, the image quality will get even worse.
5.	A Schmidt Newtonian reflector just put an aspherical correct lens before 
light reach the spherical mirror. If it is a single aspherical surface, only 
1 time better than normal Newtonian. Even double aspherical surface can 
perform nearly perfect image (diffract limit). The aspherical gap limited 
companies to enter this field, that’s why it got high price.
6.	A Maksutov Newtonian use a thick meniscus lens instead. It only has 
similar performance as a single aspherical surface Schmidt Newtonian but 
larger chromatic. Deadly curved thick spherical surface is not very easy to 
be made, need thick blank plate and grind plenty of glass.
7.	Cassegrain? They do not as good as you think, especially in coma. 
Aspherical surfaces are hard to build, the obstruction in diameter reach 
terrified 35-50% if it is a middle or short focus one. This makes the image 
low contrast and large spot size.

Coming out in 1940s, Lurie-Houghton type catadioptric telescope using a 
negative lens and a positive lens to correct the spherical mirror.
It only gets a bit distortion at the edge while performing nearly perfect 
image in whole field.
All 5 surfaces are all spherical and easy to be made.
It is not sensitive for the axis, distance or the surface radius change. 
Although you may get low accuracy lenses or assemble to not the exact place, 
you still can have excellent image.
You can choose the cheapest optical glass - BK7, very low cost.

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Now, after finding and inquiring in many ways, I had already made comment 
with one Chinese optical company whose quote is the lowest. I will order 10 
sets of lenses, which will be used for 127mm diameter (effective 
diameter=125mm), F/5 L-H catadioptric telescope. Please find attached 
layout, 4 lenses in each set:
(For copyright issue, all curve radius and thickness data not disclosed)
a.	Circle BK7 positive lens, radius=63.5, ?wave length accuracy, coat MgF2 
on both surfaces, a radius=10 hole in the center
b.	Circle BK7 negative lens, radius=63.5, ?wave length accuracy, coat MgF2 
on both surfaces, a radius=10 hole in the center
c.	Circle plate glass mirror, radius=63.5, 1/8 wave length accuracy in one 
surface, coat Argentums plus oxidized Silicon, only rough grind in the other 
surface.
d.	Elliptical plate glass mirror, radius in long axis=17.7, radius in short 
axis=12.5, 1/8 wave length accuracy in one surface, coat Argentums plus 
oxidized Silicon, only rough grind in the other surface.

Price for each set is US$150 (post fee included), for those who want to 
purchase please send the money to me, than I will pay for 10 set (or more, I 
wish) to the optical company, we will get goods after around 1 month.

Welcome any question: ukyochen888@hotmail.com

What are you still waiting for? Take action! Be ready to build up your best 
telescope, let everybody who had watched through it cheers!

Best Regards,
Ukyo Chen

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