Maksutov Vs Schmitt?

[Spier24]

What are the benefits of having a Schmitt cassegrain over a maksutov cassegrain? I've been trying to find out for a while but I haven't actually come across anything? The only assumption I've come to so far is that Schmitt's tend to have wider apertures which make them slightly better for deep sky objects.

[Louis D]

From my understanding, SCTs tend to have faster f-ratios of f/10 or f/6.3, are easier to use with field flatteners/correctors, have larger central obstructions and thus lower contrast, and can be made in larger apertures because the corrector plate is fairly thin.  The thinness of that corrector plate makes them more delicate for shipping (I've read reports of multiple SCT corrector plates cracking in shipment, but not of a single Mak plate).  They don't seem to hold collimation very well, have both field curvature and off axis coma, and tend to suffer from mirror flop and focuser slop on direction reversal.

Maks tend to have slower f-ratios and smaller central obstructions as a result yielding higher contrast, are generally limited to 7" for their largest apertures (although there have been larger such as AP's 10") due to the mass of their thick corrector plate.  This thick corrector plate is difficult to break accidentally.  They tend to hold collimation very well, often for years at a time.  They don't seem to suffer from field curvature or off axis coma as much as SCTs.  There don't appear to be any Mak focal reducers on the market, so you're stuck with f/12 or higher f-ratios.  And lastly, mirror flop and focuser slop seem to be better controlled, perhaps because the primary mirror size tops out at a more manageable size.

Edited January 3, 2021 by Louis D

[johninderby]

It should be Mak, SCT and Classical Cassegrain really. Competatively priced classical cassegrains are fairly new.

Had a few maks and SCTs and now have a 6” and 8” Classical Cassegrain. No dewing problems, quick cooldown and a crayford focuser and a fixed primary so zero mirror flop. Find they will take higher magnification than a mak or SCT and hold collimation extremely well. F/12 so inbetween most maks and SCTs of similar aperture.

Just another choice worth adding to the mix.

Edited January 3, 2021 by johninderby

[jambouk]

Louis DJ’s post answers the question. Nice.

[Peter_D]

An advantage of a  SC over a comparable Mak can be the weight saving.

Just checked what a typical OTA weighs:

Celestron C8 (200mm) : 5.7 kg

SW Mak 180: 7.8 kg

So possibly easier to mount if you compare these two examples.

 

Collimation: I  have a used Meade SCT 8 inch and a bought new Celestron 6SE.

The Meade has needed to be collimated once in the 6 months since I bought it. There was quite a bit of focus shift - I bought a Crayford focuser which works well but obviously weighs more.

The Celestron arrived in perfect collimation and has retained its collimation for a year. My C6 also displays no focus shift. It's been an excellent performer. 

Edited January 3, 2021 by Peter_D

[chiltonstar]

An important question is what do you want to do with your scope, whether you choose an SCT, MCT or something else? Each scope has certain advantages and disadvantages and will appeal to different groups. For example, expert planetary imagers often use C11s or C14s (SCTs), double star enthusiasts are more likely to use an MCT or refractor. Some say that SCTs are better "general purpose" instruments (although usually compromises tend to please no one) and certainly when I chose a 180 Mak the runner up in my decision making process was a C8 (Celestron SCT)

Personally, I like the short tube and closed optics of both designs - I live in an area with farming all around, and on many occasions the air is thick with dust which is easy to remove from the front of a corrector, more difficult from the surfaces of the primary and secondary of some other designs. 

Just an opinion.....

Chris

[M40]

I like topics like this, straight forward question, straight forward answers and you always learn something. I think it's been covered very well in the previous answers so my simple comparison between the Skymax 180 and the C8 OTA: the MAK is heavier, has a longer focal length and is cheaper.

You can get specific collimation knobs for the SCT which should tell you something giving a plus for the Mak as I've never had to collimate it. Negative for the Mak, reducers don't work when fitted at the visual back but do at the eyepiece so you are more or less stuck with the Focal Length. I also added a second focuser for the Skymax as the mirror flop was an issue for me. As mentioned earlier, if mirror flop is not so much of a problem on the MAK, I would definitely need to budget for one on the C8. 

Enjoy

[Nik271]

As for mirror flop as a 180 Skymax owner I measured mine looking at Mars near opposition, it was almost the width of the planet, i.e. 20 arcseconds. Not a problem visually but for imaging it can be a real pain when focusing.

It seems that mirror flop seems to be highly dependent on individual models, for example my 127 Mak has no mirror flop I can detect visually (of course it also works at smaller focal length).

The high end models from Orion Optics UK for Mak and the Celestron Edge HD for SCT claim not to have any mirror flop, but are quite expensive.

[chiltonstar]

2 hours ago, Nik271 said:

As for mirror flop as a 180 Skymax owner I measured mine looking at Mars near opposition, it was almost the width of the planet, i.e. 20 arcseconds. Not a problem visually but for imaging it can be a real pain when focusing.

It seems that mirror flop seems to be highly dependent on individual models, for example my 127 Mak has no mirror flop I can detect visually (of course it also works at smaller focal length).

The high end models from Orion Optics UK for Mak and the Celestron Edge HD for SCT claim not to have any mirror flop, but are quite expensive.

I cured mine by winding the focus knob from one end to the other occasionally to spread the grease out along the bolt. Worth a try.

Chris

Edited January 3, 2021 by chiltonstar

[Spier24]

This community is so helpful! Lots of great answers from all of you without overcomplicating it. The reason I asked this is because I'm planning to buy a Schmitt as my first scope and just wanted to know how they are in comparison to Mak's.

 

The main thing I've noticed is something that was pointed out in one of the first replies, Schmitt cassegrains tend to have wider mirrors which make them more suitable for viewing DSO's than Maks. Although if you want to solely focus on lunar and planetary observation then something like a skymax 127 will serve you well.

[Spier24]

7 hours ago, chiltonstar said:

An important question is what do you want to do with your scope, whether you choose an SCT, MCT or something else? Each scope has certain advantages and disadvantages and will appeal to different groups. For example, expert planetary imagers often use C11s or C14s (SCTs), double star enthusiasts are more likely to use an MCT or refractor. Some say that SCTs are better "general purpose" instruments (although usually compromises tend to please no one) and certainly when I chose a 180 Mak the runner up in my decision making process was a C8 (Celestron SCT)

Personally, I like the short tube and closed optics of both designs - I live in an area with farming all around, and on many occasions the air is thick with dust which is easy to remove from the front of a corrector, more difficult from the surfaces of the primary and secondary of some other designs. 

Just an opinion.....

Chris

That's the reason I'm thinking of going for a celestron 6 SE. Seems like a good general purpose scope that makes up for aperture where the 127 Mak lacks and focal length where a 130 or 150 Newtonian lacks. It'll be my first scope hence why I'm wanting something that's a bit of an all rounder.

[RobertI]

8 hours ago, Nik271 said:

As for mirror flop as a 180 Skymax owner I measured mine looking at Mars near opposition, it was almost the width of the planet, i.e. 20 arcseconds.

Crikey - that makes me realise how bad my C8 is - at very high magnifications the object can disappear from the field of view when focussing! It is twenty years old mind you. 
 

Just for clarification for the OP, my understanding is that ‘mirror shift’ is the problem you get when focusing and ‘mirror flop’ is another problem you get when the scope moves around the sky. I guess if you get one you are likely to get the other... 

[Merlin66]

In scope designs where the main mirror moves on a baffle tube (ie SCT, Mak etc) the flop/slop can be minimised by running the focus through full travel in/ out a few times. (about 30 turns of the knob in a SCT).

This re-spreads the grease between the baffle and the mirror slider and reduces the clearances and hence the slop. Should be done regularly.

 

[HollyHound]

I have both the Celestron C5 (SCT) and Skywatcher Skymax 127, and they both make excellent, easy to mount scopes.

The C5 has an f6.3 focal reducer fitted permanently now, bringing its focal length down to approximately 800mm and makes a lovely grab and go scope. It gives a good deal more aperture than my 80mm refractor and is mostly used for DSOs. I am also going to try using this as an EEVA scope too. Collimating is very good and can be easily adjusted, but I’ve only had to do it once. The focuser is actually very smooth with minimal (if any) mirror flop. It’s also very lightweight and can easily be carried outside on ScopeTech Zero mount and Report tripod.

The Mak 127 has a 1500mm focal length, superb contrasts views and I use it primarily for lunar and double star viewing. It arrived superbly collimated and hasn’t needed adjusting since. The binoviewer works well on this scope too. This is a little heavier than the C5 but can also be carried out on the same mount setup.

There is a very good review/comparison here, which highlights the strengths and weaknesses of each scope:

C5: http://www.scopeviews.co.uk/CelestronC5XLT.htm
Mak 127: http://www.scopeviews.co.uk/SW127Mak.htm

They complement each other very well... If I had to choose one, I’d go for the C5 as it’s more “general purpose” and with the focal reducer, is effectively two scopes in one 👍

Gary

[Merlin66]

Just noticed Chris beat me to this suggestion!

 

[Spier24]

1 hour ago, HollyHound said:

I have both the Celestron C5 (SCT) and Skywatcher Skymax 127, and they both make excellent, easy to mount scopes.

The C5 has an f6.3 focal reducer fitted permanently now, bringing its focal length down to approximately 800mm and makes a lovely grab and go scope. It gives a good deal more aperture than my 80mm refractor and is mostly used for DSOs. I am also going to try using this as an EEVA scope too. Collimating is very good and can be easily adjusted, but I’ve only had to do it once. The focuser is actually very smooth with minimal (if any) mirror flop. It’s also very lightweight and can easily be carried outside on ScopeTech Zero mount and Report tripod.

The Mak 127 has a 1500mm focal length, superb contrasts views and I use it primarily for lunar and double star viewing. It arrived superbly collimated and hasn’t needed adjusting since. The binoviewer works well on this scope too. This is a little heavier than the C5 but can also be carried out on the same mount setup.

There is a very good review/comparison here, which highlights the strengths and weaknesses of each scope:

C5: http://www.scopeviews.co.uk/CelestronC5XLT.htm
Mak 127: http://www.scopeviews.co.uk/SW127Mak.htm

They complement each other very well... If I had to choose one, I’d go for the C5 as it’s more “general purpose” and with the focal reducer, is effectively two scopes in one 👍

Gary

 

1 hour ago, Merlin66 said:

Just noticed Chris beat me to this suggestion!

 

 

 

That's why I'm going for it. As a beginner I think having a general purpose scope is good at it gives you a feel for observing objects within our solar system as well as DSO's. Then when you have a feel for both you can buy a scope that is best suited towards what you prefer. Either a good mak or a large Newtonian.

[Merlin66]

Spier24,

My comment was Re the spreading of the grease on the baffle of SCT's etc.

 

[SiriusB]

SCT cools down quicker due to thinner corrector plate~ (apparently), never owned an SCT, must add to my'astro to do' list.

I can  say, even my small mak 127 takes a good while to cool down properly...

Also My Mak's never yet needed collimation since i bought it & initially adjusted up.

Apparently SCT's are often out of collimation,though there's plenty of info out there on how to tackle this, so no biggie.

 

[Pete Presland]

I swapped my Mak180 for a SCT C9.25, because i wanted a bit more versatility with my scope. The slightly shorter focal length and abilty to use a reducer have certainly given me this. Planetary imaging wise, which is what i do most, i am not sure there is a huge difference in the two scopes.

The collimation of my C9.25 has been pretty solid, maybe this down to its hardly ever transported anywhere. The mirror slop was much worse on my Mak180, than the C9.25. That said, my Crayford has pretty much removed the issue.

[chiltonstar]

4 hours ago, Pete Presland said:

I swapped my Mak180 for a SCT C9.25, because i wanted a bit more versatility with my scope. The slightly shorter focal length and abilty to use a reducer have certainly given me this. Planetary imaging wise, which is what i do most, i am not sure there is a huge difference in the two scopes.

The collimation of my C9.25 has been pretty solid, maybe this down to its hardly ever transported anywhere. The mirror slop was much worse on my Mak180, than the C9.25. That said, my Crayford has pretty much removed the issue.

I'm surprised the 9.25 isn't significantly better than the 180 Mak for planets - I would have thought the 30% increase in aperture would have showed??

Adding a decent focuser to my 180 Mak was also very worthwhile (thanks to @johninderby for the advice) - it has made double star and planetary focusing SO much easier!

One point not mentioned so far, don't C8s only have a 1 1/4" back unlike the 180 Mak (I could be wrong).

Chris

[Pete Presland]

2 hours ago, chiltonstar said:

I'm surprised the 9.25 isn't significantly better than the 180 Mak for planets - I would have thought the 30% increase in aperture would have showed??

Adding a decent focuser to my 180 Mak was also very worthwhile (thanks to @johninderby for the advice) - it has made double star and planetary focusing SO much easier!

One point not mentioned so far, don't C8s only have a 1 1/4" back unlike the 180 Mak (I could be wrong).

Chris

I think much is made of the increases in aperture and I can only speak from personal experiences. I didn't  think there is much difference imaging wise,  maybe the highly rated schott glass in the Mak makes up for the slightly smaller aperture.

[RT65CB-SWL]

From my experience of being the owner of a C6/SCT and an ETX105 Mak., is collimation. With the SCT they are on the front of the corrector plate and there are three collimation screws. With the ETX series* you have to remove the flip-mirror housing on the rear to access them and it has the two sets of collimation screws, (as on the classic 'Newtonian' reflector), i.e. one for adjustment and one for locking. As my ETX105 has been since re-modded with a solid backplate following an accident after the ABS flip mirror housing got damaged and broke two of three mounting points. I have to remove it to gain access to the collimation screws. (images below). 

The three blue countersunk/motorcycle/go-kart fairing washers hold the backplate of my 're-modded' ETX105 to the OTA. This has to be removed before I get access to the collimation screws. 

Link here with images of what a Meade ETX Mak., should look like... http://spottingscopes.name/meade-etx-105-105mm-maksutov-optical-tube-spotting-scope-telescope-with-uhtc.htm

 

* not sure about other brands of Maksutov OTA other than 'Sky-Watcher', as the collimation screws can be accessed without having to disassemble the backend from what I have seen.