6" Cassegrain Telescopes: What are the main differences between...

... a Schmidt, a Maksutov and a Ritchey-Chretien?

I would like to buy one of these and cannot decide. I will use it for observations, especially of the planets, and to take photos with my Olympus E-M5-III camera.

Please advise, thanks a lot.

An R-C design is mainly used for imaging. Yes, you can observe with it but most RC owners are imagers. Budget R-C designed scopes are best avoided because they do require a lot of tuning and that is usually where they save money in the build.

Maks are usually much slower and longer focal lengths so imaging faint dso's will require much longer exposures. The advantage of Maks is that longer focal length makes them great for planetary imaging. Also, as far as I know, there's no collimation to worry about with a Mak design as the secondary is fixed to the back of the front meniscus lens.

Regular SCT's are the most common and best all-around scopes for visual and imaging for beginners. Collimation is required but don't let that scare you. Plenty of YouTube videos to show you how. After a few tries it becomes second nature.

Personally, I'm a refractor snob now after growing up using Newtonians and SCT's and a couple of Maks. I just sold my Mak127mm.

Nothing beats a really nice APO.... let the comments begin. ;-)

RC is basically a SCT modified for improved Coma at the edges of the field of view. The is the same optical design in the Hubble space telescope. A Maksutov Cass.. Is a different design with a thicker convex front corrector lens. It is optically slower, usually around F15 compared to the F10 optics of the SCT scopes. The Mak would typically give a higher magnification, higher contrast, and sharper image for planets and separating double stars. However, their more narrow field of view and slower optics are not well suited for those faint, fuzzy dark sky objects. A SCT or it’s RC variant would be better suited for general purpose astrophotography, whereas a Mak. Cass. Is more specialized for planetary imaging. Another option are Mak. Newtonians. They are typically faster than SCT and Mak Cass., have a similar near APO image quality of the Mak Cass., and are well flat field corrected and no field flattener are required compared to imaging with a standard Newtonian or refractor. The main disadvantage of the Mak. Newt. Is the large tube size that acts like a sail that has a lot of shake in wind if put on a lighter German equatorial (GEQ) mount. SCT and MC scopes are often on fork mounts which would be more rigid than a large scope on a GEQ mount. Some smaller SCTs are on a single arm instead of a fork mount. If you won the Lottery, a 6” APO refractor would be my choice as it would blow the others away in IQ.

An RC has nothing in common with a SCT or Mak. It has no optical corrector plate and relies on 2 hyperbolic mirrors instead. Because of the mirror design, collimation is extremely difficult and can be likened to trying to balance one bowling ball on top of another. Their native focal ratio is also generally much faster than a SCT or Mak.

Just a quick point on an SCT scope regarding collimation. Is IS possible that things can get out of alignment, but it is NOT an every day thing.

I bought the original Celestron C-8 in '78, still in collimation. I treat it well and it has always held up. If it did go out, there are 3 screws to tweak to get it back.

Cheers

Edit: Regarding fork mounts. My Celestron is fork mounted and it is ok for visual, but still pretty wobbly for imaging. If buying a new scope now I would want to a GEQ, mount.

I plan to make a gizmo to stiffen up the Celestron, now that I am getting more into imaging. There some HUGE scopes on fork mounts but they are in a whole 'nother league.

RC definitely not recommended for newcomers, from what I have read.

82Virago said:

Just a quick point on an SCT scope regarding collimation. Is IS possible that things can get out of alignment, but it is NOT an every day thing.

I bought the original Celestron C-8 in '78, still in collimation. I treat it well and it has always held up. If it did go out, there are 3 screws to tweak to get it back.

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Two aspherical mirror (Ritchey Chretiens and variants) cassegrains can be almost impossible to collimate. Not for beginners.

Maksutovs do not temperate well unless in a climate where night time temperatures fall pretty fast. In my climate even a 7 inch Maksutov almost never reach termal equilibrium because the thick corrector lens. And they are slow at f/15 or so.

In my view the Schmidt Cassegain (like a Celestron 6 inch) offer the perfect compromise between price, size, optical quality and ease of collimation.

My personal telescopes however are all small refractors...

82Virago said:

Cheers

Edit: Regarding fork mounts. My Celestron is fork mounted and it is ok for visual, but still pretty wobbly for imaging. If buying a new scope now I would want to a GEQ, mount.

I plan to make a gizmo to stiffen up the Celestron, now that I am getting more into imaging. There some HUGE scopes on fork mounts but they are in a whole 'nother league.

RC definitely not recommended for newcomers, from what I have read.

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Seems like a good read. ;-)

I'd argue that the mount is just as important as the optics. My Meade ETX105 was good for visual viewing of Jupiter, but pretty hopeless as soon as I used long exposures. Does the lack of comment above about mounts indicate that they've now been sorted?

M Stewart said:

I'd argue that the mount is just as important as the optics. My Meade ETX105 was good for visual viewing of Jupiter, but pretty hopeless as soon as I used long exposures. Does the lack of comment above about mounts indicate that they've now been sorted?

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Good mounts are still important. Mounts are kind of sorted, buy a cheap one and you are stuck. Spend quite a bit more to be happy. ;-)

But the initial question was about telescopes.

Belgarchi said:

... a Schmidt, a Maksutov and a Ritchey-Chretien?

I would like to buy one of these and cannot decide. I will use it for observations, especially of the planets, and to take photos with my Olympus E-M5-III camera.

Please advise, thanks a lot.

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Well, thanks all, I bought an Orion Maksutov-Cassegrain 6".

Now, I need a sky without clouds (very rare this year on the coast of Massachusetts!), a better mount (the cheap $100 I am using is totally inadequate) and tune better my finder (6x30), I have a tough time finding specific stars or planets.

The best advice I could give you at this point if you want to get into serious astrophotography is to buy the best mount you can afford. In astronomy, all EQ mounts have a weight rating, and the consumer level mounts should never be loaded with more than about 50-60% of that weight capacity. Example, if the mount is rated to handle a payload of 50 lbs, your imaging rig should not exceed about 25-28 lbs. 30lbs would be pushing it in my opinion.
Of course, the super high-end mounts like 10Micron, Paramount, etc can handle better than 75% of their weight capacity.

Your scope weighs in at 12.4lbs, a guide scope is going to add another 1lbs and a camera probably another 2-3lbs. With that said, you want to buy a mount rated to handle at least 30lbs.

NevadaDesertSkies said:

The best advice I could give you at this point if you want to get into serious astrophotography is to buy the best mount you can afford. In astronomy, all EQ mounts have a weight rating, and the consumer level mounts should never be loaded with more than about 50-60% of that weight capacity. Example, if the mount is rated to handle a payload of 50 lbs, your imaging rig should not exceed about 25-28 lbs. 30lbs would be pushing it in my opinion.
Of course, the super high-end mounts like 10Micron, Paramount, etc can handle better than 75% of their weight capacity.

Your scope weighs in at 12.4lbs, a guide scope is going to add another 1lbs and a camera probably another 2-3lbs. With that said, you want to buy a mount rated to handle at least 30lbs.

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The OP's new scope is only for planetary. The mount really doesn't matter when your shooting video at 150 FPS......An EQ5/Sirius is more than sufficient...

swimswithtrout said:

The OP's new scope is only for planetary. The mount really doesn't matter when your shooting video at 150 FPS......An EQ5/Sirius is more than sufficient...

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From the OP: "I would like to buy one of these and cannot decide. I will use it for observations, especially of the planets, and to take photos with my Olympus E-M5-III camera."

Where in his post does he say it will ONLY be used for planetary? I'm just trying to help the guy out.

NevadaDesertSkies said:

swimswithtrout said:

The OP's new scope is only for planetary. The mount really doesn't matter when your shooting video at 150 FPS......An EQ5/Sirius is more than sufficient...

Click to expand...

From the OP: "I would like to buy one of these and cannot decide. I will use it for observations, especially of the planets, and to take photos with my Olympus E-M5-III camera."

Where in his post does he say it will ONLY be used for planetary? I'm just trying to help the guy out.

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Does not matter.

The telescope he got has 1800 mm focal lenght at f/12.

Fine for solar (with a proper filter), lunar and planetary work. Not much for deep sky...

If planets are first, there is a fourth option Takahashi Mewlon(s) 210

https://www.takahashiamerica.com/takahashi-mewlon-m-210-reflector.html

Its a Dall - Kirham design - if you can find a Tak CN 212 Cassegrain - Newtonian - its a wicked planet killer too with the similar DK optical train but has removable secondary mirrors to go to F 3.9 Newtonian.

https://optcorp.com/products/takahashi-mewlon-210-dall-kirkham-telescope-ota

BION The finder scope is a carrying handle and in 20 years + with a CN 212 - carrying it , hoisting it has never effected the finder's accuracy or the collimation of the main mirror.

I would get a hard case for it with wheels.

--
Best Regards, Rodger
Save Lives - Be an Organ or Stem Cell Donor.
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NevadaDesertSkies said:

swimswithtrout said:

The OP's new scope is only for planetary. The mount really doesn't matter when your shooting video at 150 FPS......An EQ5/Sirius is more than sufficient...

Click to expand...

From the OP: "I would like to buy one of these and cannot decide. I will use it for observations, especially of the planets, and to take photos with my Olympus E-M5-III camera."

Where in his post does he say it will ONLY be used for planetary? I'm just trying to help the guy out.

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It's an f12, long focal length Mak completely unsuitable for anything besides lunar/planetary. It's what it's made for. If the OP has intentions of shooting DSO's, he needs a different scope.