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Why Call SCTs Master of None?

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#1 kel123

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Posted 05 May 2021 - 07:51 PM

At native focal lengths, SCTs are planet and galaxy killers.

Add a focal reducer, it becomes as fast or even faster than most doublet refractors.

Talk about the hyperstar, then it is most EAA practitioners', and a lot of astrophotographers' dream as it becomes the fastest scope in the game.

Yet, recently, I have read more and more threads whereby , if one person says something about the versatility of the design, some other person calls it master of none.

Even if it doesn't really excel at widefield like refractors, what about the insane speed with hyperstar?

What about the planet and galaxy killing reputation? How is it not a master here?

If it is not a master of something, which design is?

Why the bad rap?
 

#2 BlueMoon

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Posted 05 May 2021 - 08:02 PM

 

Add a focal reducer, it becomes as fast or even faster than most doublet refractors.

Talk about the hyperstar, then it is most EAA practitioners', and a lot of astrophotographers' dream as it becomes the fastest scope in the game.

There's your answer. Modifications.  Spend more $$$ to do what refractors can already do without the mods. Then SCT's lack the light gathering ability of a reflector in their same size class. There are always exceptions but I'm speaking in generality.

 

My 0.02. Clear skies.


 

#3 descott12

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Posted 05 May 2021 - 08:12 PM

I love my SCT. I go from f2 to f20 on a regular basis. Nothing anywhere close as versatile.

I do some visual stuff, EAA, planetary imaging, white light solar and spectroscopy all with the same scope and just a few add-on accessories.


 

#4 kel123

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Posted 05 May 2021 - 08:35 PM

There's your answer. Modifications. Spend more $$$ to do what refractors can already do without the mods. Then SCT's lack the light gathering ability of a reflector in their same size class. There are always exceptions but I'm speaking in generality.

My 0.02. Clear skies.


It is a planet and galaxy killer without adding anything.
 

#5 dcaponeii

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Posted 05 May 2021 - 08:41 PM

It is a planet and galaxy killer without adding anything.

Let's not forget planetary nebulae and globular clusters.  About the only thing I shoot with my refractor are emission nebulae.


Edited by dcaponeii, 05 May 2021 - 08:41 PM.

 

#6 dnrmilspec

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Posted 05 May 2021 - 08:43 PM

All true.  Hyperstar is a game changer.   The most "fun" scope I ever had was an 11" Celestron on a CI-700 mount.  It did everything very well.  My 8" Ultima 2000 with hyperstar is a real winner too.  Great optics and F2.  Really the hot ticket though older.

 

I think SCTs are highly underrated. 


 

#7 kel123

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Posted 05 May 2021 - 08:47 PM

Let's not forget planetary nebulae and globular clusters. About the only thing I shoot with my refractor are emission nebulae.


Exactly.
 

#8 BlueMoon

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Posted 05 May 2021 - 08:48 PM

It is a planet and galaxy killer without adding anything.

Let's not forget planetary nebulae and globular clusters.  About the only thing I shoot with my refractor are emission nebulae.

Zero sum answers.

 

Nothing that can't be done by a decent refractor or reflector as well. 

Frankly, I don't think there is an definitive answer to your "Master of none" question. All scopes are a compromise in some way.

 

Clear skies.
 


Edited by BlueMoon, 05 May 2021 - 08:53 PM.

 

#9 kel123

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Posted 05 May 2021 - 08:53 PM

Nothing that can't be done by a decent refractor or reflector as well. Zero sum answer.

Clear skies.


Not at that resolution.
 

#10 GGK

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Posted 05 May 2021 - 09:06 PM

I prefer to think of the SCT as the Near Master of All.
 

#11 Jon Isaacs

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Posted 05 May 2021 - 09:19 PM

At native focal lengths, SCTs are planet and galaxy killers.

Add a focal reducer, it becomes as fast or even faster than most doublet refractors.

Talk about the hyperstar, then it is most EAA practitioners', and a lot of astrophotographers' dream as it becomes the fastest scope in the game.

Yet, recently, I have read more and more threads whereby , if one person says something about the versatility of the design, some other person calls it master of none.

Even if it doesn't really excel at widefield like refractors, what about the insane speed with hyperstar?

What about the planet and galaxy killing reputation? How is it not a master here?

If it is not a master of something, which design is?

Why the bad rap?

 

The SCT design is inherently compromised.  Consider visually:

 

My 4 inch TeleVue is capable of a 4.9° TFoV with a flat field free of aberrations.  I don't know any SCT that can do that. It's a master of that realm.

 

For the planets, the large CO reduces contrast, optical quality is good but a Newtonian with a premium mirror and a small CO, a premium Mak, a large refractor, these can be the masters of the planets and double stars, depending on the situation.

 

For globulars and galaxies, aperture is king.  This the realm of Newtonians/Dobs for visual.

 

Master of none simply means for any given application, there's something else that would the first choice.  

 

SCTs are versatile, compact in the smaller and medium sizes, affordable.

 

Jon


 

#12 Tangent

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Posted 05 May 2021 - 09:50 PM

Every telescope is a compromise.

 

Compared to a reflector, an SCT is more compact, and affords a more comfortable viewing position.

 

Compared to a refractor, an SCT provides a more affordable aperture.

 

Of course they do come with some downsides, including a limited FoV and cooling issues. 


 

#13 bobzeq25

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Posted 05 May 2021 - 09:51 PM

Here's why "master of none".

 

SCTs use spherical mirrors to save money.  That involves some compromise.  Hyperstar is an add on 3rd party device.  More optical compromise.

 

They were invented by a person who figured out how to make a corrector lens cheaply.  Spherical mirror, (inexpensive) corrector lens (inexpensive), and you have a great low cost scope, justifiably popular.  But the design has fundamental optical issues.  So no one uses it for really high end scopes.

 

I have what I believe is the least compromised spherical mirror design, a C8 RASA.  It only does one thing, but it does it well.  Doing just one thing makes that possible.  No compromise, except for the spherical mirror.  Still, not the best fast reflector.

 

Perhaps the best fast reflector is the Officina Stellare.  The mirror is spherical, kind of.  It's coated on the back, the light is corrected by passing through the mirror twice, and the front has a different radius.  A "Riccardi-Honders".  An 8 inch is $10,000.

 

For long focal length, a Corrected Dall Kirkham, also designed to do just one thing, with an ellipsoidal primary mirror, and corrective lenses, works better than an SCT.   $$$  A 12.5 inch (smallest they sell) Planewave is $8500.

 

SCTs are marvelous high quality inexpensive scopes.  But the optical design is fundamentally not as good as more expensive optical designs, and no amount of quality in manufacture can overcome that.  Hence, "master of none".


Edited by bobzeq25, 05 May 2021 - 09:56 PM.

 

#14 TOMDEY

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Posted 05 May 2021 - 09:58 PM

Well... in the Cats & Casses & SCTs forum, detraction would be in poor taste. So I'll just list all of the advantages of SCTs >>>

 

> the eyepiece is at a convenient location and doesn't move around a lot

> the corrector plate prevents the primary mirror from getting dirty

> friends and relatives are impressed just looking at it

> cheap eyepieces work fine with it

> the giant central obstruction means finger prints on the middle don't matter

> you can warm up your hands on the dew-not running at max

> it's fun to (try to) collimate it... which exercise builds patience, character, and arbitrarily-delayed gratification

> the drive noises keep you alert

> at intended eff-ten exposures are nice and long... plenty of time to whistle and relax

> the field is nice and small so as to not overwhelm

> unlike an equivalent Dobsonian, the 14-incher is nice and portable

> made in ... where are they made now?

> they're blue or orange, which are attractive colors

> the half-yoke makes a fine tuning-fork

 

That pretty well exhausts the superlatives.    Tom

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#15 PJBilotta

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Posted 05 May 2021 - 09:58 PM

Very good for most observing, but not exceptional in any. This isn't necessarily a bad thing, as few designs are more versatile.

 

Come to think of it, SCTs are the best at somethimg. There is simply no other design that packs 8 inches of aperture into such a compact, lightweight tube, that performs very well for most types of observing. Refractors don't have the aperture. Newts don't have the portability. Maks don't have the shorter focal length for wider field views. None can be both a slow f/10 scope, a faster f/6.3, and a hyper-fast f/2.

 

So, I guess the SCT is the master of something most observers need: versatility.


Edited by PJBilotta, 06 May 2021 - 11:04 AM.

 

#16 kel123

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Posted 05 May 2021 - 10:00 PM

Maybe we should compare it with scopes at its price level. It should be a master at something when it comes to that price level.
 

#17 Jaimo!

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Posted 05 May 2021 - 10:19 PM

popcorn.gif


 

#18 RalphMeisterTigerMan

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Posted 06 May 2021 - 12:53 AM

What I love about my C5+? Small and portable. I keep it in my modest sized room with all the accessories, hidden in plain sight and no one can tell! 

 

Clear skies and keep looking up!

RalphMeisterTigerMan


 

#19 TOMDEY

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Posted 06 May 2021 - 03:14 AM

Actually --- as much as I criticize SCTs (I've owned then divested two 14-inchers) --- I still think I'd like to buy a plain vanilla Meade SCT 16-incher Alt-Az; install in a little dome strictly for fun visual use friends and family kinda stuff. My current 36-inch Dob in a dome and 16-inch True Binoscope just aren't casual star-party safe (to the hardware or casual visitors) or comfortable. So all we use with family are the small fun scopes from the deck attached to the house.

 

Ehhh... Let's see how much a 16-inch Meade costs. Well, there it is $15K without a tripod or wedge. It would fit comfortably right in the middle of a smallish dome. And an 8-foot basic Explora Dome on 10-ft round building is another $7K and site prep, electricity, etc. around $3K. Plus tax NYS 8%. Pushes it up to $27K. Which is consistent with the 2x the instrument by time all is said and done. And I shouldn't be tossing another $30K around with all the other projects I have going on. That would stress my wallet and my bandwidth. Well --- that was fun to at least consider and postpone... most likely forever.

 

This is 4am pipe-dream grist. Can anyone there familiar with SCTs give me an opinoin on what I've outlined above? Would that be comfortable for strictly visual use? Have I missed anything? Strictly visual lazy GoTo relaxation under darkish SQM 21.4 rural sky 100 feet from the house.    Tom


 

#20 Nippon

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Posted 06 May 2021 - 03:15 AM

It seems that the SCT solved a lot of problems for observers in the 60s and 70s who were more and more needing to pack their scopes into a car and drive to a dark site. And the EQ mounted 8 to 10" Newtonians of the day were not really travel friendly. But as far as the design itself being compromised I wonder why their are almost no SCTs built by premium telescope makers. The only one I can think of is the short lived Takahashi 225. So why is that the case. In almost every design of telescope there are lower cost brands and premium high end brands but not the SCT for some reason.


 

#21 luxo II

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Posted 06 May 2021 - 05:31 AM

Kel, you’d best stick to your SCT, for your own peace of mind.

gve.gif


Edited by luxo II, 06 May 2021 - 04:47 PM.

 

#22 bobhen

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Posted 06 May 2021 - 06:05 AM

The SCT design is inherently compromised.  Consider visually:

 

My 4 inch TeleVue is capable of a 4.9° TFoV with a flat field free of aberrations.  I don't know any SCT that can do that. It's a master of that realm.

 

For the planets, the large CO reduces contrast, optical quality is good but a Newtonian with a premium mirror and a small CO, a premium Mak, a large refractor, these can be the masters of the planets and double stars, depending on the situation.

 

For globulars and galaxies, aperture is king.  This the realm of Newtonians/Dobs for visual.

 

Master of none simply means for any given application, there's something else that would the first choice.  

 

SCTs are versatile, compact in the smaller and medium sizes, affordable.

 

Jon

What Jon said. 

 

SCTs are popular because they are compact, and for many amateurs that is a more desirable benefit than is the absolute best optical quality.

 

Bob


 

#23 jgraham

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Posted 06 May 2021 - 06:46 AM

Jack of all trades and master of none?

Sounds about half right. :)

The 8" SCT has been popular for a very long time for some very good reasons, it is a master at being a general purpose telescope.

Some say silly things. :)
 

#24 Angeles

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Posted 06 May 2021 - 06:53 AM

The sct haters will always be sct haters

 

I mean to compare a high end 4" apo that cost $4000 to a $800 8"sct , well the 8 sct can collect 16x the light

 

you cant really get a 8" f/8 or f/10 anymore you would have to get this custom made now and then with high end mirrors as  said put this scope in to the 1000's

 

the normal is 8"f/5 and or the 8"f4 quatrro type is the norm,

 

compare the 8sct to a huge dob? have you ever put a 24 to 30" in a regular car (sedan) with a family of 4 or 5? i dont think it will happen. the 8" sct even with 4 or 5 people theres still lots room for this scope and ther regular camping stuff for the family. Also how is a 8 to 12 ft ladder even portable or safe or easy.

 

I still rather use my 12" sct lx 90 compared to a huge 24" dob thats 12 ft tall needs a tall ladder move it by hand, collimate it etc

 

The 8" sct is 15 inches long and 12 lbs whats smae size and lighter then this?

 

here is a youtuber that shows 3 types of scopes and why the sct does have its place.

 

 

https://youtu.be/HFgjI9XTXWk


Edited by Angeles, 06 May 2021 - 06:58 AM.

 

#25 erin

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Posted 06 May 2021 - 07:06 AM

Very good for most observing, but not exceptional in any. This isn't necessarily a bad thing, as few designs are more versatile. Come to think of it, SCTs are the best at somethimg. There is simply no other design that packs 8 inches of aperture into such a compact, lightweight tube, that performs very well for most types of observing. Refractors don't have the aperture. Newts don't have the portability. Maks don't have the shorter focal length for wider field views. None can be both a slow f/10 scope, a faster f/6.3, and a hyper-fast f/2. So, I guess the SCT is the master of something most observers need: versatility.

Well said Peter! This is exactly why I ended up with an SCT for my “big” scope instead of a big mak. The versatility made the difference.


 


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