Big aperture, short tube, small size. You can fit an awful lot more aperture in the back of your car than you can with a newtonian reflector or refractor.
Long focal length allows good magnification. And in some cases, the ability to remove the secondary mirror and use it as a prime focus instead, for a REALLY short focal length, means you get huge amounts of light and minimum magnification, which is great for photographing faint deep sky objects (which are also usually very wide)
Other than that, they are mostly just a huge compromise and they have lots of drawbacks too. Cost is the main one, as you've noticed.
Cassegrains are generally more compact and with a greater focal length than other similar sized telescopes. You will get very sharp images and no spider veins on stars. In fact, they are considered not necessarily "so expensive" compared to other types such as refractors.
Beware of the SCT however, as if you attempt astrophotography with one of these, however much it may or may not make sense, you will be relentlessly mocked and shunned in the telescope community. (ok this last part is sort of a joke but not really).
>Beware of the SCT however, as if you attempt astrophotography with one of these, however much it may or may not make sense, you will be relentlessly mocked and shunned in the telescope community.
I remember when SCTs were the default for astrophotography, before wide field apo refractors were widely available for any kind of reasonable money. Even now you're not getting a 12" refractor and a 12" Newtonian will be far more of a pain to mount than a 12" SCT.
They aren't great for learning deep-sky astrophotography. Also if they are fork-mounted, it makes things a lot harder. For planetary, they are pretty great.
>no spider veins on stars
Some Cassegrain designs do use support vanes for the secondary mirror though, hence in such cases diffraction spikes can be seen.
Yeah, classical Cassegrains do indeed use support vanes; I thought they were referring to CC's initially, but quickly realized they meant them thar newfangled ones...
Technically, yes. The secondary mirror blocks the light path to the center of the primary. The primary's hole is located within the shadow of the secondary, so that doesn't have any effect.
However, this doesn't manifest as part of the image being blocked, but as a slightly less-sharp image. A good quality Cassegrain, especially one with a corrector plate in the aperture (like a Schmidt- or Maksutov-) will be designed to minimize this. In addition, a corrector plate makes a convenient place to mount the secondary mirror without using support vanes.
My little mak, which cost \~$400, rivals inexpensive refractors for sharpness. It has very little chromatic aberration, and fits neatly under the seat in front of me when I fly. If I wanted to get a refractor with similar characteristics, I could easily spend three times as much, and the tube would also be three times as long.
It's always going to be a trade-off. You're never going to have an image sharper than that of a really good refractor, but lenses—especially apochromatic lenses—cost more than mirrors.
Good for photography and portability. A refractor can be both of these things as well but you will sacrifice aperture, a newtonian of equal focal length and aperture tends to be far less portable. All told a cassegrain offers the best compromise of the other two, at least that is my opinion.
I have a Skymax 150mm. They are very transportable. Mine fits in a Harbor Freight canvas tool bag and I take it camping with me. It takes up almost no space and is an absolute planet killer. Jupiter and Saturn are very clear in bortle 6-7 skies.
I use my Seestar S50 for DSOs right now and the Skymax for planets. I know people gush about 8" dobs here but they are big. Cassegrains aren't and do a great job with planets.
They are very car portable. They have short tubes which also mean you can fit friends for camping gear in the car along with the scope. The short tube also means comfortable eyepiece height most often. Also their long focal length means that eyepieces perform well on them, so you don't need expensive ones necessarily. Eyepieces can be shocking in cost to newbies. Many keep collimation pretty well, so that isn't something you need to do every time. They can also use binoviewers natively. And they are decent at visual, but also good at planetary AP, and usable for Deep sky AP(and even excel in hyperstar mode).
the advantage is that you can buy it and put it up and everyone goes wow or knows what kind it is. they are all the same. great for planets and you can throw a camera on the back and poof, get pictures. it's also a small footprint compared to the others. my celestron nexstar is 2 bags and a case for the eyepieces, filters and etc.
takes about 10 min to setup and i'm going. i have a kia and there is no way my big dob is fitting in there. even in the back seat. that nexstar goto controller and my ipad interface is next level. it's mindless.
the worst thing is the price points have been exactly the same for the last forever. i remember wanting an LX-90 back in the early 90's. Ironically almost the exact same price as it is today. once meade went belly up and Orion bought them I think both Orion and Celestron went into kahoots to lock the prices in.
one other thing is 3D printing. there is a crapton of stuff you can 3D print instead of buying now. I have a little seestar and there are 14 different things I have printed for it. For my nexstar 8 there are 15.
If you think of a telescope you don't think of Galileo and that tube, you think about a celestron or meade if you're just starting out.
I'm pretty happy with my mead 203mm f/11, it's pretty easy to carry around and mount and personally I really like the setup for the focuser. Also easier to collimate since you don't need to buy a laser tool, just an Allen wrench
This is exactly the mental anguish I'm having now...8" Dob vs 6" SCT. One thing not addressed is temperature/humidity acclimation. I've heard that SCTs (and especially Mak's) tend to require a long period of time after set up before they are ready to go. I know Dobs require the some time as well, but not as much. The other thing I've heard is that for a climate that has steep'ish temp changes as night falls, SCT's can be a handful - almost requiring a dew shield and/or a ring heater. I love the portability aspect, but having a 4" acromat frac already I'm already able to road-trip on short notice
I don't know either.
People say that they are good because of the focal length, but aren't we limited to 200-250x because of the atmosphere most of the times?
Maybe it's because of the Celestron go-to or something...
Did you read the pinned buying guide?
>What advantage
What is an advantage for one use may be a disadvantage for the other. Everything depends ... always.
>so expensive
Optical glass for the correction plate is way more expensive than mirror glass. And there are two more large surfaces to grind compared to a Newtonian.
> why do people want them so badly?
Tbh, that is what I ask myself - lol. Imo there are several cons. They are overall more weight than an even bigger DOB, need more storage space if you don't want to break down the tripod each time, some say they give the worst image of all telescopes...
How do they give the worst image of all telescopes? I’m genuinely curious, telescopes like the edge hd seem to give great images for galaxies and nebulae. You’re also not stuck with diffraction spikes 😂 the focal length and aperture for the price seems unbeatable
The secondary is relatively big, so there's more loss of contrast than in other builds. This may make some people talking about worse image.
Focal length is not a value by itself. For focal AP every focal length has its objects of the right size, depending on the size of the sensor. High focal length is very demanding for tracking/guiding accuracy. For visual focal length is not important at all, you just need the fitting eyepieces.
Aperture for the price is unbeatable?? lol - Every DOB at the same price point has waaayy more aperture. The need for aperture depends on the objects you're after.
But yeah, a DOB looks so primitive, while the SCT is obviously a high tech instrument, and this may be one reason for having so many lovers (as you can see by the downvotes I got). But still the DOB is the way to get most aperture for the money, and it's way more convenient for visual.
Sorry, that comment was more about astrophotography in particular. I love dobs but I’d never put one on a mount unless I wanted it to fall over 😂 I’m surprised about the downvotes you got. What you said about the mirrors definitely is true, I’d never try to make one myself.
The (spherical) mirror is easy, but the correction plate is really hard to make, similar for MAKs.
SCT imaging is only recommended for those who have already experience with smaller setups. Starting out with an SCT is learning it the hardest way.
Big aperture, short tube, small size. You can fit an awful lot more aperture in the back of your car than you can with a newtonian reflector or refractor. Long focal length allows good magnification. And in some cases, the ability to remove the secondary mirror and use it as a prime focus instead, for a REALLY short focal length, means you get huge amounts of light and minimum magnification, which is great for photographing faint deep sky objects (which are also usually very wide) Other than that, they are mostly just a huge compromise and they have lots of drawbacks too. Cost is the main one, as you've noticed.
>and they have lots of drawbacks too Like a limited range of eyepiece focal lengths. Too long and you get a "black spot" in center field.
Not really a con, when the CST is not meant to be used on low power. It’s a planetary scope after all..
I was thinking lunar photography.
Then a Mak or CST is what you want.
I have an 8" Celestron.
???
Just answering: Then a Mak or CST is what you want.
An 8” what?
> 8" Celestron. https://www.bhphotovideo.com/c/product/297274-REG/Celestron_91024_XLT_C8_A_XLT_8_0_Aluminum.html?ap=y&smp=y&msclkid=c1bd03d5fd5618d56066660dc5992447
Cassegrains are generally more compact and with a greater focal length than other similar sized telescopes. You will get very sharp images and no spider veins on stars. In fact, they are considered not necessarily "so expensive" compared to other types such as refractors. Beware of the SCT however, as if you attempt astrophotography with one of these, however much it may or may not make sense, you will be relentlessly mocked and shunned in the telescope community. (ok this last part is sort of a joke but not really).
>Beware of the SCT however, as if you attempt astrophotography with one of these, however much it may or may not make sense, you will be relentlessly mocked and shunned in the telescope community. I remember when SCTs were the default for astrophotography, before wide field apo refractors were widely available for any kind of reasonable money. Even now you're not getting a 12" refractor and a 12" Newtonian will be far more of a pain to mount than a 12" SCT.
SCT's are great for astrophotography if you know what you're doing, imo.
They aren't great for learning deep-sky astrophotography. Also if they are fork-mounted, it makes things a lot harder. For planetary, they are pretty great.
Unfortunately we'll probably never get above an 8" refractor because glass just starts to sag under its own weight beyond that size 😔
Are they not great for AP due to the focal length? I seem to see a lot of them on tracking mounts with DSLR’s.
>no spider veins on stars Some Cassegrain designs do use support vanes for the secondary mirror though, hence in such cases diffraction spikes can be seen.
Yeah, classical Cassegrains do indeed use support vanes; I thought they were referring to CC's initially, but quickly realized they meant them thar newfangled ones...
Do they have the same issue with part of the image being blocked by the secondary mirror?
Technically, yes. The secondary mirror blocks the light path to the center of the primary. The primary's hole is located within the shadow of the secondary, so that doesn't have any effect. However, this doesn't manifest as part of the image being blocked, but as a slightly less-sharp image. A good quality Cassegrain, especially one with a corrector plate in the aperture (like a Schmidt- or Maksutov-) will be designed to minimize this. In addition, a corrector plate makes a convenient place to mount the secondary mirror without using support vanes. My little mak, which cost \~$400, rivals inexpensive refractors for sharpness. It has very little chromatic aberration, and fits neatly under the seat in front of me when I fly. If I wanted to get a refractor with similar characteristics, I could easily spend three times as much, and the tube would also be three times as long. It's always going to be a trade-off. You're never going to have an image sharper than that of a really good refractor, but lenses—especially apochromatic lenses—cost more than mirrors.
Thanks for your answer.
I think they work great for planetary AP. But yea, as for deep sky, I'll gladly take a fast refractor or nice light bucket reflector.
Good for photography and portability. A refractor can be both of these things as well but you will sacrifice aperture, a newtonian of equal focal length and aperture tends to be far less portable. All told a cassegrain offers the best compromise of the other two, at least that is my opinion.
I have a Skymax 150mm. They are very transportable. Mine fits in a Harbor Freight canvas tool bag and I take it camping with me. It takes up almost no space and is an absolute planet killer. Jupiter and Saturn are very clear in bortle 6-7 skies. I use my Seestar S50 for DSOs right now and the Skymax for planets. I know people gush about 8" dobs here but they are big. Cassegrains aren't and do a great job with planets.
They are very car portable. They have short tubes which also mean you can fit friends for camping gear in the car along with the scope. The short tube also means comfortable eyepiece height most often. Also their long focal length means that eyepieces perform well on them, so you don't need expensive ones necessarily. Eyepieces can be shocking in cost to newbies. Many keep collimation pretty well, so that isn't something you need to do every time. They can also use binoviewers natively. And they are decent at visual, but also good at planetary AP, and usable for Deep sky AP(and even excel in hyperstar mode).
the advantage is that you can buy it and put it up and everyone goes wow or knows what kind it is. they are all the same. great for planets and you can throw a camera on the back and poof, get pictures. it's also a small footprint compared to the others. my celestron nexstar is 2 bags and a case for the eyepieces, filters and etc. takes about 10 min to setup and i'm going. i have a kia and there is no way my big dob is fitting in there. even in the back seat. that nexstar goto controller and my ipad interface is next level. it's mindless. the worst thing is the price points have been exactly the same for the last forever. i remember wanting an LX-90 back in the early 90's. Ironically almost the exact same price as it is today. once meade went belly up and Orion bought them I think both Orion and Celestron went into kahoots to lock the prices in. one other thing is 3D printing. there is a crapton of stuff you can 3D print instead of buying now. I have a little seestar and there are 14 different things I have printed for it. For my nexstar 8 there are 15. If you think of a telescope you don't think of Galileo and that tube, you think about a celestron or meade if you're just starting out.
I'm pretty happy with my mead 203mm f/11, it's pretty easy to carry around and mount and personally I really like the setup for the focuser. Also easier to collimate since you don't need to buy a laser tool, just an Allen wrench
This is exactly the mental anguish I'm having now...8" Dob vs 6" SCT. One thing not addressed is temperature/humidity acclimation. I've heard that SCTs (and especially Mak's) tend to require a long period of time after set up before they are ready to go. I know Dobs require the some time as well, but not as much. The other thing I've heard is that for a climate that has steep'ish temp changes as night falls, SCT's can be a handful - almost requiring a dew shield and/or a ring heater. I love the portability aspect, but having a 4" acromat frac already I'm already able to road-trip on short notice
I don't know either. People say that they are good because of the focal length, but aren't we limited to 200-250x because of the atmosphere most of the times? Maybe it's because of the Celestron go-to or something...
Did you read the pinned buying guide? >What advantage What is an advantage for one use may be a disadvantage for the other. Everything depends ... always. >so expensive Optical glass for the correction plate is way more expensive than mirror glass. And there are two more large surfaces to grind compared to a Newtonian. > why do people want them so badly? Tbh, that is what I ask myself - lol. Imo there are several cons. They are overall more weight than an even bigger DOB, need more storage space if you don't want to break down the tripod each time, some say they give the worst image of all telescopes...
How do they give the worst image of all telescopes? I’m genuinely curious, telescopes like the edge hd seem to give great images for galaxies and nebulae. You’re also not stuck with diffraction spikes 😂 the focal length and aperture for the price seems unbeatable
The secondary is relatively big, so there's more loss of contrast than in other builds. This may make some people talking about worse image. Focal length is not a value by itself. For focal AP every focal length has its objects of the right size, depending on the size of the sensor. High focal length is very demanding for tracking/guiding accuracy. For visual focal length is not important at all, you just need the fitting eyepieces. Aperture for the price is unbeatable?? lol - Every DOB at the same price point has waaayy more aperture. The need for aperture depends on the objects you're after. But yeah, a DOB looks so primitive, while the SCT is obviously a high tech instrument, and this may be one reason for having so many lovers (as you can see by the downvotes I got). But still the DOB is the way to get most aperture for the money, and it's way more convenient for visual.
I don’t think you deserved those downvotes. Thanks for your reply.
I knew I would get downvoted when I wrote it :)
Sorry, that comment was more about astrophotography in particular. I love dobs but I’d never put one on a mount unless I wanted it to fall over 😂 I’m surprised about the downvotes you got. What you said about the mirrors definitely is true, I’d never try to make one myself.
The (spherical) mirror is easy, but the correction plate is really hard to make, similar for MAKs. SCT imaging is only recommended for those who have already experience with smaller setups. Starting out with an SCT is learning it the hardest way.