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Is RC not a Cat?

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#1 skyskan

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Posted 23 August 2019 - 10:57 PM

I might end up making myself looking completely stupid with this question, but I might just go for it since I cannot stop thinking about it.

I thought I know this without any doubts that Ritchey-Chretien telescope is a variant of catadioptric telescope. However, I just noticed there are far more RC listing under Reflector in classified, rather than Cats and Casses. Is my understanding completely wrong? If not, why are we not listing RCs under Cats and Casses?

#2 Boom

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Posted 23 August 2019 - 11:00 PM

An RC is not a Cat.  It is a Cass.  This forum is Cats AND Casses.  So it belongs here.  

 

Perhaps Cats OR Casses might make a more appropriate forum title scratchhead2.gif


Edited by Boom, 23 August 2019 - 11:04 PM.

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#3 skyskan

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Posted 23 August 2019 - 11:01 PM

Ism’t cat a abreviation for catadioptric?
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#4 Boom

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Posted 23 August 2019 - 11:08 PM

Ism’t cat a abreviation for catadioptric?

 

Yes, and that means an optical system made up of BOTH lenses and mirrors, such as a Mak or SCT.  The RC in basic form only has the primary and secondary mirrors, and no refractive lens elements, so it is not a Cat.  The RC light path is folded in a Cassegranian configuration however, which makes it a variation of a Cass.


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#5 skyskan

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Posted 23 August 2019 - 11:13 PM

Yes, and that means an optical system made up of BOTH lenses and mirrors, such as a Mak or SCT. The RC in basic form only has the primary and secondary mirrors, and no refractive lens elements, so it is not a Cat. The RC light path is folded in a Cassegranian configuration however, which makes it a variation of a Cass.

Thanks, I some how thought rc is a variant of sct.

So, it belongs to casses category. I guess many users consider it reflector and put the listing under Reflectors in clssified since it does not have any refractor component.

Edited by skyskan, 23 August 2019 - 11:19 PM.


#6 Boom

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Posted 23 August 2019 - 11:19 PM

Thanks, I some how thought rc is a variant of sct.

No problem.

 

The SCT is a Cat and a Cass at the same time.  However, the RC only qualifies as a Cass.


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#7 Boom

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Posted 23 August 2019 - 11:24 PM

Thanks, I some how thought rc is a variant of sct.

So, it belongs to casses category. I guess many users consider it reflector and put the listing under Reflectors in clssified since it does not have any refractor component.

 

Yea, that would be their bad lol.gif

 

You might have mixed up the RC with the Celestron Edge and Meade ACF scopes.  The latter two are variations of the SCT.  

 

 

Edit:  It doesn't help that when Meade first released the ACF design, they called it the "Advanced Ritchey Chretien".  A couple RC manufacturers took Meade to court over this, on the basis that Meade's RC branding was misleading.  After this, Meade changed the name to Advanced Coma Free.


Edited by Boom, 23 August 2019 - 11:29 PM.

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#8 Littlegreenman

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Posted 23 August 2019 - 11:47 PM

Both SCTs ad Cassegrains are "folded" optics. The light is bounced between 2 (or more ) mirrors. By doing this the tube can be much shorter than a basic reflector, "folding" the light path back more than once through the same length of the tube. Both mirrors can made to correct for optical aberrations can be made. So they share that, and both are short tubes, which can confuse things.

 

One think I don't understand, is there any problems with the photons going in direction in the tube colliding with photons going in the opposite direction? 

(sorry)


Edited by Littlegreenman, 24 August 2019 - 04:57 AM.

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#9 skyskan

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Posted 24 August 2019 - 12:20 AM

One think I don't understand, is there any problems with the photons going in direction in the tube colliding with photons going in the opposite direction?
(sorry)

Photons almost always get to see the back of their friends and family traveling in front of them. In very rare occasion, they go face to face when photons in front of them hit a mirror and change their travel direction more than 90 degrees. That is when they can say hello and see each others. They actually enjoy that moment. They believe in that moment will come, but not many photons actually experience that miraculous moment. We are doing favor when we use reflectors. With cats and casses, we are doing double favor.

Edited by skyskan, 24 August 2019 - 12:27 AM.

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#10 TOMDEY

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Posted 24 August 2019 - 12:29 AM

The textbook definitions for the three traditional, passive imaging lens categories are:

 

Catoptric = comprising only powered reflective surfaces

Dioptric = comprising only powered refractive elements

Catadioptric = comprising both powered reflective surfaces and powered refractive elements

 

The unpowered elements (folding flats, deviating prisms, windows, filters, etc.) don't enter into the categorizations, and refractive field groups are sometimes not included in the definition, especially if they are optional add-ons near the image surface (field group, coma-corrector, telecompressor, telextender, field-flattener. etc.). Diffractive, active (powered flat lens) and gravitational imaging are outside of these traditional three categories. Powered Gradient Index elements are considered Dioptric, even though they (may) have unpowered (flat) surfaces.

 

That pretty much covers it. When in doubt, common sense almost always guides which of the three to assign.

 

Anyway... the whole topic is only 1% optics and 99% semantics. What the community chooses to call it --- doesn't affect its performance at all! Your telescope doesn't give a hoot what you call it; Pluto can care less what you call it... but Clyde might!   Tom


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#11 Boom

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Posted 24 August 2019 - 12:37 AM

Anyway... the whole topic is only 1% optics and 99% semantics. What the community chooses to call it --- doesn't affect its performance at all! 

 

Thanks for the textbook definitions.

 

Let's just say I'm glad the Bird Jones Newtonians aren't filed under this forum.


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#12 Astrojensen

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Posted 24 August 2019 - 01:31 AM

Let's just say I'm glad the Bird Jones Newtonians aren't filed under this forum.

It actually should be, since it's a catadioptric. 

 

 

Clear skies!

Thomas, Denmark


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#13 Boom

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Posted 24 August 2019 - 01:32 AM

But I'm glad it's not.
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#14 sg6

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Posted 24 August 2019 - 01:43 AM

Think the naming depends on the detail of the mirrors used.

You have spherical, parabolic and hyperbolic and the different ones used make up the type of scope.

 

I think they were all termed "Compound" as they used assorted mixtures, an SCT has a corrector plate at the front - it is not quite flat glass, not sure of the Maks. Think they use 2 spherical mirrors accurately positioned, unsure of the lump of glass at the front of them.

 

How about a diferent thought?

Is an RC different to a Newtonian?

2 mirrors and a hole for the optical path to exit from the scope.

Mirrors are a different shape - detail, and the hole is in a mirror not in the tube assembly, but still a hole doing the same job.


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#15 Boom

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Posted 24 August 2019 - 01:49 AM

Not going to over think this.

The RC light path is Cassegrain. It is not diverted to the side like a Newtonian.
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#16 Littlegreenman

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Posted 24 August 2019 - 05:08 AM

The textbook definitions for the three traditional, passive imaging lens categories are:

 

Catoptric = comprising only powered reflective surfaces

Dioptric = comprising only powered refractive elements

Catadioptric = comprising both powered reflective surfaces and powered refractive elements

 

The unpowered elements (folding flats, deviating prisms, windows, filters, etc.) don't enter into the categorizations, and refractive field groups are sometimes not included in the definition, especially if they are optional add-ons near the image surface (field group, coma-corrector, telecompressor, telextender, field-flattener. etc.). Diffractive, active (powered flat lens) and gravitational imaging are outside of these traditional three categories. Powered Gradient Index elements are considered Dioptric, even though they (may) have unpowered (flat) surfaces.

 

That pretty much covers it. When in doubt, common sense almost always guides which of the three to assign.

 

Anyway... the whole topic is only 1% optics and 99% semantics. What the community chooses to call it --- doesn't affect its performance at all! Your telescope doesn't give a hoot what you call it; Pluto can care less what you call it... but Clyde might!   Tom

When I fist go into this hobby 25 years ago, I was enthralled by strange telescope designs, some which may fit into the three classes above, but may fit better into simply weird or unusual telescope.

Some links:

A site for weird telescopes

http://www.eyes-on-t...g/shs/weird.htm

 

A book...:

https://www.amazon.c...y/dp/052148393X


Edited by Littlegreenman, 24 August 2019 - 05:10 AM.

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#17 TOMDEY

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Posted 24 August 2019 - 07:35 AM

When I fist go into this hobby 25 years ago, I was enthralled by strange telescope designs, some which may fit into the three classes above, but may fit better into simply weird or unusual telescope.

Some links:

A site for weird telescopes

http://www.eyes-on-t...g/shs/weird.htm

 

A book...:

https://www.amazon.c...y/dp/052148393X

Yes, I have that book... read it several times! He categorizes according to how many mirrors, etc., and also categorizes mount types by how many axes, location of the image, and other countable classification metrics.

 

Although it still remains semantics, it's a good way to survey the subject. And, one should not forget the zero and infinity limits. For example, the zero-element telescope is the no telescope at all option --- plain naked eye observing, like when we just go out and look up! In that case, the magnification is one, the system is binoscopic rich-field (full object-space luminance) and the Field of View is two pi (the entire hemisphere above the horizon). The infinity dioptric element telescope is the gradient index lens... which can be thought of as an infinite number of differentially-weak powered surfaces, splayed in-line, serially (which is indeed how lens design programs model them). An infinite-axis mount would be the earth-bound ball scope or the zero-G floating satellite. And those are just scratching the surface in opening up, as Martin Harwit put it... "Observational Phase-Space."    Tom 


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#18 luxo II

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Posted 24 August 2019 - 08:36 AM

I thought I know this without any doubts that Ritchey-Chretien telescope is a variant of catadioptric telescope


RC are “catoptric” have only reflecting elements.
“Dioptric” refers to designs that have only refracting elements (ie refractors).
“Catadioptric” refers to scopes that involve refracting and reflecting elements - SCT and Maksutovs.

RC are also Cassegrains and in this respect do belong in this forum.

Tom beat me to it :(

Edited by luxo II, 24 August 2019 - 08:39 AM.

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#19 skyskan

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Posted 24 August 2019 - 03:11 PM

You might have mixed up the RC with the Celestron Edge and Meade ACF scopes.  The latter two are variations of the SCT.  

 

 

Edit:  It doesn't help that when Meade first released the ACF design, they called it the "Advanced Ritchey Chretien".  A couple RC manufacturers took Meade to court over this, on the basis that Meade's RC branding was misleading.  After this, Meade changed the name to Advanced Coma Free.

Yes, I do have 8" Meade ACF.  Maybe that is where the misunderstanding started, but it cannot be an excuse for not understanding the system correctly.

 

However, is RC far more desirable comparing to other cat and casses to the extent to insist false claim or raise a lawsuit over the term?  It is not like Ritchey and Chretien got mad and suing Meade for falsely using the their trade mark.  Do others have right to the term or optical design?

 

Is it really that desirable to endure a lawsuit? 


Edited by skyskan, 24 August 2019 - 03:14 PM.


#20 TOMDEY

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Posted 24 August 2019 - 03:36 PM

Yes, I do have 8" Meade ACF.  Maybe that is where the misunderstanding started, but it cannot be an excuse for not understanding the system correctly.

However, is RC far more desirable comparing to other cat and casses to the extent to insist false claim or raise a lawsuit over the term?  It is not like Ritchey and Chretien got mad and suing Meade for falsely using the their trade mark.  Do others have right to the term or optical design?

Is it really that desirable to endure a lawsuit?

Interesting point! Indeed, tradename is, literally, exclusive right to a coined word, in perpetuity!

 

I was working at Kodak, when Polaroid sued and won damages for instant film infringement. Kodak had to pay up and destroy the entire inventory of a huge warehouse. Kodak slid into oblivion after that... and Polaroid shortly thereafter. Neither company enjoyed the fat days again. Ironically... about all that was left of marginally-significant value was --- their Names!    Tom


Edited by TOMDEY, 24 August 2019 - 03:36 PM.

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#21 skyskan

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Posted 24 August 2019 - 03:57 PM

Interesting point! Indeed, tradename is, literally, exclusive right to a coined word, in perpetuity!

 

I was working at Kodak, when Polaroid sued and won damages for instant film infringement. Kodak had to pay up and destroy the entire inventory of a huge warehouse. Kodak slid into oblivion after that... and Polaroid shortly thereafter. Neither company enjoyed the fat days again. Ironically... about all that was left of marginally-significant value was --- their Names!    Tom

Does any entity have the trademark on Ritchey-Chretien?  Also, is RC far better than other Cats and Casses?

 

 

I miss Elmgrove campus and Kodak.  I miss Rochester when they were going strong.  It was a very nice city back then.  How is the city these days?



#22 TOMDEY

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Posted 24 August 2019 - 05:09 PM

Hi, skyskan! I highly doubt that Ritchey-Chretien would be in any way exclusive... other than that it ~should~ only refer to optical imaging systems that comprise a two-mirror front end PM and SM that correct both spherical and coma. And yes indeed, the RC, properly executed, is a magnificent configuration. And that includes proper alignment, which is rare among most of our amateur stuff.

 

Rochester, sigh... has gone the way of most all of the other east and west coast cities... seen far far better days.    Tom


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#23 skyskan

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Posted 24 August 2019 - 05:18 PM

Rochester, sigh... has gone the way of most all of the other east and west coast cities... seen far far better days.    Tom

Too bad...

 

I really miss busy sunny summer days in Midtown Plaza..... and the hotdog stand in front of it.  Rochester International Airport even had immigrations and duty-free shops.

I strongly hope things get better for that city.



#24 bbqediguana

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Posted 24 August 2019 - 05:19 PM

According to this article on Sky & Telescope:

 

https://www.skyandte...s-bury-hatchet/

 

It was Star Instruments and RC Optical Systems who sued Meade over "false advertising" for Meade referring to its RCX series and its LX200R series as "advanced Ritchey-Chrétien" designs. Both of those companies sold Ritchey-Chrétien based optical systems so I'm sure both were quite upset when mass-producer Meade tried to use the moniker.

 

Thanks!

 

Rick


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