Telescope Names

Dazzler · #1 11-05-2007, 12:14 PM

If anyone has the time could someone please give me a basic run down on the difference between the most popular telescope designs, i.e SCT, Newtonian, Dobsonian, Mak etc.

I have an LX200R which is a Ritchey Cretien. I understand that there is a difference in the optical system between this and that of the old LX200 SCT but I don't know much about other types of reflectors.

When describing my scope to friends I struggle to be able to explain the difference between my RC and an SCT as they look ostensibly the same.

I also note that there are a number of conbinations out there i.e. Newtonian-Cassegrain etc. How does this all work in a description for a layman like myself?

Also are refractors just refractors and then there is a variety of reflectors or is there also a variety of refractors out there?

Thanks

jase (Jason) · #2 11-05-2007, 12:48 PM

Quote:

Originally Posted by Dazzler

I have an LX200R which is a Ritchey Cretien. I understand that there is a difference in the optical system between this and that of the old LX200 SCT but I don't know much about other types of reflectors.

Actually what you have is a modified SCT. The Ritchey Cretien design does not use corrector plates or lenses. Meade and other resellers of their products got into some trouble over this - http://www.star-instruments.com/lawsuit.html

Sorry, if you believed the marketing blurb that you bought an RC.

ballaratdragons (Ken) · #3 11-05-2007, 01:25 PM

Darren,

The list of variations is almost endless! There are even designs that not many people have heard of like the 'Kletsov' (which Bert uses), Dall-Kirkham, Gregorian, Shmidt-Vaisala, Argunov, etc etc.

But there are basic ones that are more common: Schmidt-Cassegrain, Schmidt-Newtonian, Maksutov, which all use a very similiar optical system with variations in mirror shape, and corrector plates.

Refractors have mainly 3 configurations: Achromat, ED/Semi Apochromat, and Apochromat. Each having better quality lenses progressively.

and the list goes on.

Kal (Andrew) · #4 11-05-2007, 01:43 PM

Quote:

Originally Posted by jase

Actually what you have is a modified SCT. The Ritchey Cretien design does not use corrector plates or lenses. Meade and other resellers of their products got into some trouble over this - http://www.star-instruments.com/lawsuit.html

Sorry, if you believed the marketing blurb that you bought an RC.

Actually, meade and the resellers didn't get into trouble yet. The judge has already thrown out most of the plaintiffs claims: source.

As was previously reported in the Company's Annual and Quarter Reports filed with the SEC, the Company stated that a lawsuit was filed in September 2006 (which was later amended on October 31, 2006) by Star Instruments and RC Optical Systems, two competitors of Meade, that alleged that the Company and several dealers falsely advertised that Meade's award winning RCX400 and LX200R telescopes employ Ritchey-Chretien technology. In their lawsuit, Star Instruments and RC Optical Systems accused Meade and its dealers of, among other causes of action, engaging in racketeering, conspiracy and RICO violations, as well as deceptive business practices, dilution of an established trademark and product disparagement. All of these claims were dismissed and the judge rejected plaintiffs' request to file an amended complaint. In addition, the judge rejected RC Optical's claim for treble damages, thereby eliminating most of the money damages sought by RC Optical and its co-plaintiffs.

Having said all that, I too own a Meade LX200R and I would not consider it an 'Advanced Ritchey-Chretien' either.

jase (Jason) · #5 11-05-2007, 02:21 PM

Thanks for the latest lawsuit update Andrew.

"What's in a name?", you ask...
You can clearly see that Meade's LX200R and RCX optics (a.k.a aplanatic schmidt cassegrain) do not compare to the performance of an RC (see below attachments of spot diagrams).

For a complete/comprehensive guide to optical designs and performance, I've found the following link to be excellent.
http://www.telescope-optics.net/inde...LE_OF_CONTENTS

Warning to those mathematically challenged - the contents of some web pages may hurt your brain.

Dazzler · #6 11-05-2007, 05:08 PM

and to think I believed I had a baby Hubble!

Not trying to be parochial but I have no complaints at all with my scope. It gets me (a near novice) to objects with very little effort and seems to produce great viewing, although I have little to compare with at this stage.

My purpose for this thread though was to gain a basic understanding of what makes a Dob a Dob, a Newt a Newt etc etc.

ballaratdragons (Ken) · #7 11-05-2007, 05:53 PM

A Dob is a Newt!

It is the mount that makes the difference. A dob is a Reflecting Newtonian Telescope in a Dobsonian Base

The same Reflector in an EQ mount just gets called a Reflector.

sheeny (Al) · #8 11-05-2007, 06:26 PM

G'Day Darren,

I'll jump in and I'm sure others will correct me when I'm not so correct!

Most refractors are a "straight through" type of arrangement - light goes in the front and comes out the back, basically. As mentioned before there are achromats, semi-apochromats and apochromats, which are successively more complex (and usually better quality) lenses to reduce chromatic aberration.

There are heaps of different reflector designs, but the main ones are:

Cassegrain - light comes in the front, reflects off a parabolic mirror at the back (the primary) then of a much smaller secondary mirror at the front and finally comes out through a hole in the centre of the primary mirror.

The Scmidt-Cassegrain (SCT) is a variation on this which includes a corrector plate (a lens) at the front to correct some optical defects in the mirror shapes. SCTs are usually either fork mounted or equatorially mounted.

Newtonian - light comes in the front, reflects off the primary at the back, then off the much smaler secondary mirror at the front which is at 45 degrees to the axis if the tube, so the light exits out the side near the top. Newts are most often mounted equatorially or in dobsonian bases.

A Schmidt-Newt once again has a corrector plate at the front.

Hope this helps,

Al.