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maksutov cassegrain compared to Refractors


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Hi,  Sorry firstly if this is a basic question.

I have been looking around for a while now to find an answer,  but so far no real luck,, so i thought it was best to ask here.

Basically I have a few questions that i am looking at.

So for visual only,

1. If i was to be looking at starts and double stars,  would a maksutov cassegrain show them up as nice clear pin dots or would the Refractor be the better option here?

2.  For Nebular and galaxies, would the maksutov cassegrain be better for viewing them or the Refractor?

3.  For viewing planetary,  would the maksutov cassegrain be better for viewing them or the Refractor?

 

Then for astrophotography,  would the choices chance or be pretty much the same?

I realise that all this might be a very broad question,  but just trying to make up my mind on either a 180/2700 maksutov cassegrain  or a 130 Triplet refractor,

Any advice is appreciated.

Thanks.

 

 

 

 

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I used a roll of the stuff that B&Q sell for insulating behind radiators; Al on one side and polystyrene on the other. Makes the scope look a bit hubble'ish, but this is what it looks like:-

As a matter of fact, Mike Clements in Utah did buy such a spare blemished spy mirror and built this.  Apparently, it has a permanent home now. Does this make you wish the UK had a const

My Intes Micro 815 Deluxe Mak Cassegrain will easily beat a top shelf APO 6-inch refractor on resolution and light grasp and is more apochromatic than any of them. it has a system Strehl ratio of

Posted Images

G'day @bluesilver.

I will attempt to answer as best as possible in order, from my limited experience, as I own a C6/SCT, a 're-modded' ETX105 [Maksutov/Mak/MCT] and a 70mm semi-achro refractor. I am also purely visual.

  1. Assuming the your Maksutov is new, collimation should be 100% spot-on and stars and double stars appear as pin-points of light. Same for a refractor too.
  2. For nebular, galaxies, other DSO's maybe not as they tend to cover vast areas. Therefore a wide-field refractor will be better.
  3. For planetary viewing then the Maksutov or refractor, (100mm or better for a refractor), is going to awesome views at the e/p.

For astro-photography the triplet should be OK. You will need a sturdy and polar aligned mount for DSO's. The more experienced astro-photography SGL'ers will advise and give more to this question.

 

IMG_0385.JPG.5061fa1a4073478117544c4770b199ed.JPG

Images above & below showing my 're-modded' ETX105.

PIC021.JPG.317e3ab5bc2a32848d576782c9caf3ab.JPG

 

Unfortunately, no 'scope does all in this hobby... and I have one to many TeleVue 13mm e/p's :thumbsup:...

PIC044.JPG.54acb21c9b4e6e69cda54fdd37a1defe.JPG
left: 13mm Plossl - centre: 13mm Nagler / Type 1 - right:  13mm Nagler / Type 6... :evil62:

Edited by Philip R
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All things being equal (unfortunately they never are!), a Maksutov should give similar images to a refractor and at 150mm aperture and larger will cost less and be easier to mount due to its compactness. The downside is that the Maksutov will take much longer to reach thermal equilibrium, the fast primary optics being more affected by this and the passage of the light three times through the tube, one close to the tube wall and one through a narrow internal baffle tube all conspire to dilute its potential.

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I'm mainly a visual observer of the Moon and planets and for me, a good refractor is better than a good Maksutov for planetary  and lunar observations (and for all wider field observations of any objects) for the following reasons:

1   As good as Maksutov optics can be, a high quality refractor will always out perform a high quality Maksutov aperture for aperture for image quality  if they are made to the same standard.

2   Maksutovs have longer focal ratios than most refractors, hence it is  just about impossible to obtain low power/wide fields of planetary conjunctions (unless they are very close), views of the Moon going through a star cluster like the Beehive or Pleiades,  for many variable star fields and of course quite a number of deep sky subjects if that's what takes your fancy.

3  Maksutovs generally hold their collimation well, but they can go out of collimation and sometimes are delivered new needing collimation.  With a good refractor you can always be assured if it isn't giving good images it is likely to be the seeing responsible.

4   As Peter pointed out, thermal equilibrium with all but the smallest Maksutov can be a big problem, and certainly will be if you have to keep a 6 inch or larger Mak indoors and carry it out to observe - it's not often where I live it will stay clear long enough for many Maksutovs of such sizes to reach equilibrium.

 

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It’s a question of what you are looking at. For lunar / planetary maks are ideal but due to their narrow fov not good for widefield observing. There are a bit of a specialist scope but that doe#n’t matter if lunar / planetary is what you want it for. And on cost per inch of aperture a mak totaly trounces the APO and also easy to mount due to their short length. There is a reason maks are so popular.

Re: collimation. Never ever had a mak go out of colimation. Have had a couple of refractors that did though. Cool down time is no problem in the UK and I wouldn’t imagine down under where you don’t often get extreme differences in inside vs outside temps. 1/2 hour is usually good enough with a 127 mak and there is the option of sticking the scope in the shed or garage for a while before observing. BTW big fracs , particularily triplets, have a lot of glass that can take ages to cool down so they’re not immune to that.

You will notice that many people end up with a few different scopes for different purposes. A mak, a frac and a dob are a good combination. Remember observing isn’t a competetion. It’s just a hobby, something you do for enjoyment.

Edited by johninderby
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Thanks for the replies and advice.

I guess i should of mentioned that i have a 16 inch Dobsonian that i mainly use now for nebular, galaxies, and other DSO's

It is ok for Planetary and double stars,  just a bit more touchy to the seeing conditions if not so great.

 

Looks like i might have to invest in both a maksutov cassegrain and also a refractor,  but not all at once.

Sounds like the skywatcher 180/2700 maksutov cassegrain could be the pick for planetary,  and maybe the Triplet refractor for star clusters,

I am guessing the triplets are better image wise compared to the doublets

Or is there no real visual difference between the triplets and doublets unless you do serious astrophotography?

Appreciate the replies and advice.

 

 

Edited by bluesilver
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I don't think cost factor was mentioned, forgive me if i missed it but, for a third of the price of a good 120mm APO you can get a 150mm Mak and it will wipe the floor with the APO on planetary and lunar.

Saw more than my share of bewildered $3000 dollar owning APO guys look at Saturn through my Mak and leave scratching their heads. Of course, as mentioned above, they take a while longer to cool, 

have a relatively narrow field of view and, are not the best for photography  ( i have taken some great planetary images with my mak) it is a niche scope, it won't please everyone, but what it does, it does

very well. 

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Any scope with a central obstruction will have poorer double star performance aperture for aperture.  It's a simple matter of optical physics.  Stars are much more pinpoint in my little AT72ED than in my 127 Mak or 8" Dob.  For instance, the E component is much more apparent in the Trapezium with the 72ED than with either obstructed scope.  The main four stars bloat too much in the obstructed systems to see the E component.

 

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I would get an FPL-53 doublet over an FPL-51 triplet.  The correction is nearly indistinguishable and the doublet cools down quicker, is less front heavy, and tends to have fewer collimation issues.

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1 hour ago, johninderby said:

My favourite lunar / planetary scope.

 

I take it that this is the 180/2700 Skywatcher?

I have heard a few saying that this particular scope works very well on planetary with the addition of a very good diagonal in replace of the original.

20 minutes ago, Louis D said:

Have you considered using an off-axis mask on your 16" Dob to make it a 6" to 7" unobstructed system?  It would also help with punching through seeing conditions.

I haven't even thought of that idea to be honest,  sounds like something i must try.

Thanks also for the advice on the FPL-53 doublet over an FPL-51 triple,  something to keep in mind also.

Lots to research.

Appreciated.

 

 

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1 hour ago, bluesilver said:

I guess i should of mentioned that i have a 16 inch Dobsonian that...is ok for Planetary and double stars,  just a bit more touchy to the seeing conditions

Have you considered stopping down your Dob to around a 6" in such conditions?

1 hour ago, bluesilver said:

Looks like i might have to invest in both a maksutov cassegrain and also a refractor

😀 Aye, sadly not one scope is perfect at everything :icon_rolleyes:. Each type gives slightly different results and as you are aware, are better and worse in certain areas.

Not knowing the budget, I don't think you'd be disappointed with the planetary and double star performance from something like a 7" Intes-Micro Mak-Newt, a SW 180MAK, SW 120mm APO, Tak FC100, Vixen FL102 😋 and so on. In my experience, that scope x 'blows away' scope y is a little over the top and more often just not the case. Each of these scopes will have its very own list of compromises, will give slightly different results and be better in some areas and worse in others.

The other problem with lists like this is that unless you get the chance to try out the scopes yourself, at the end of the day, you'll have to follow your heart and just go for the design you think you'd like to own next. Each scope type will have its detractors and supporters based on a myriad of factors including but not limited to: local weather conditions, seeing etc, life style and family commitments, cool down, focal length, exit pupil from eyepieces, mounting requirements, portability, budget, bias towards one design over another and so on. If you could give some indication of some of these factors, perhaps it would hone and refine your enquiry a little better?

Evidently, then, as it stands, there is no right answer but with your 16" Dob already in hand my own preference would be towards purchasing a decent APO 😁

 

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Thanks again for the replies,

As for budget,  i was looking at around the same price as my Skywatcher 16 inch goto

So a SW 180MAK fits in there pretty good and at the other end getting up there is the SW 120mm APO.

But of course i will only be looking at moving into one for now.

So good research i think i need to do.

 

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@bluesilver

For comparison - I have a 180mm Russian Intes Micro Maksutov that visually slightly out performs my Japanese 128mm APO.

BUT the Mak has cooling vents at the front and a cooling fan at the back to remove warm air from the entire system and it also clears the  warm boundary layer off the surface of the primary mirror - absolutely essential if you want to get the best out of a Maksutov design without waiting for hours for it to cool.

If you can find an Intes Micro Mak then it would be worth considering as once cooled they are very sharp - although they are expensive.

However - as others have said try an off axis mask made from cardboard on your Newtonian and judge the results.

Edited by dweller25
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1 hour ago, dweller25 said:

Or mine...

Ditto.

Having tested extensively my TV-76 against my SW 127MAK on Jupiter and Saturn (2018 and 2019), I feel that a Mak would also have to be at least 150mm to be worthwhile. That was until recently with the purchase of a FL102. Not withstanding my original sentiments above, I do wonder whether an 180mm would really make much difference on Jupiter and Saturn over something like a SW 120 APO or FC-100 :icon_scratch:

 

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I doesn't count what type of telescope you have if the seeing is very poor. This year so far, using a 5" triplet and  6" doublet refractors a 7" Mak and a 16" SCT, only the SCT has given a hint of the Cassini Division.    😕

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39 minutes ago, Peter Drew said:

I doesn't count what type of telescope you have if the seeing is very poor. This year so far, using a 5" triplet and  6" doublet refractors a 7" Mak and a 16" SCT, only the SCT has given a hint of the Cassini Division.    😕

For visual and normal imging yes. For lucky imaging the larger aperture allows shorter exposures and increases your chance of being lucky!

Regards Andrew 

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51 minutes ago, johninderby said:

Don’t forget that resolution improves with more aperture. Something often overlooked. My old Equinox 120 was good on lunar / planetary but the Skymax 180 I have now gives more detal on lunar.

What you need is one of each. 😁

One of each would definitely be the ultimate solution for sure.

Think i will make up one of these off axis mask and see what i dose for me.

But so far for scope goes,  it is looking like the Skywatcher 180/2700 Mak might be the choice for the next scope and then perhaps a little down the track look at the Refractor.

It seams to read to me that if you want to lake longer exposure photos,  you are better of with a smaller aperture scope like the refractors,   could be wrong here though.

 

 

Edited by bluesilver
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