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alan potts

Sky-watcher 180mm Maksutov

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Sky-watcher 180mm Maksutov.

I got this scope a few months ago now and have a good few nights out under the stars to see what makes it tick. The scope cost about 830 pounds for me here which is not as good a deal as you can get in the UK but you have to consider I also bought the 190mm M/N at the same price, so much a case of swings and roundabouts.

When the scope arrived I collected it as always from Sofia from my friend who is the Meade/SW main dealer. I unboxed it with him in the shop, there were a few things that were in my books not up to scratch from the outset, the eyepieces and the diagonal. I asked if both of these could be passed to someone starting out as part of a purchase to help them along. With having mainly Televue accessories they were never going to be in the frame. So the box came with 5 things in it and I set off home with 2 things, the finder and the scope.

The finder is the same as the one that comes with the M/N190mm only being a different colour, though I firmly believe the quality of the black one that came with the M/N is better, it seems sharper to me.

Mounting

The main scope is not very heavy at 8kg and sits much better on the HEQ 5 pro mount than their M/N 190mm. This was my mistake believing a photo on a catalogue, why do they pull tricks like this. I was not a site member at the time and regret this every time I mount it up, someone would have told me it was not meant to be.

The mounting plate is a fair place to start as it is with the dovetail bar type of system, at first glance I was not so sure about the stability of this but after a good few outings it seems to be adequate for the job in hand, though I would have preferred a cradle mounting. I have already touched on the finder and this seems to cause a few minor problems with alignment of scope and finder. The mirror cell outer wall seems to be slightly conical and the finder shoe is attached to this. It makes it very difficult to align the scope with it as it is not pointing in the same direction, it is only slight but enough to put the fox in the hen house though easy enough to put right.

Optics,

Having tried the scope out on a good few targets, mainly Saturn, Venus the Moon and double stars, I have to say I find them excellent. It would appear this is where the lions share of the cost has been spent.

I have used the scope mainly with Televue eyepieces from 41mm Panoptic to a 7mm Nagler, the former vignettes slightly at the edges as this was never designed to be a wide field scope. I just find set-up a whole lot easier with the low power, the 35mm Panoptic does not suffer with the same problem so that gets most use. Images of the planets are very sharp with great contrast, one can see a great deal of detail with this piece of equipment. I bought it to try and take my mind away from the dream of a 6 inch APO and to a large extent I think it is working. The quality of airy disc at higher powers is almost as good as my APO 115mm which cost 4 times more, so high praise indeed.

One thing that I have read from many members about these scopes is cooling time. Last night I took the scope from the basement which was at a temperature of 24 degrees to outside at 29.2 thinking this will not be a problem, even after an hour it was still showing turbulence that was from the scope and not the general seeing. These members knew what they were talking about and have even read these scopes should stay outdoors.

The one area where I feel Sky-watcher have really dropped the baby is the visual back. This is part of what is sold as a good quality scope, not the most expensive on the market but not the cheapest either. The visual back is terrible, the set screws feel as if they are going to strip the thread they sit in and the whole assemble is of poor quality. I hope I can upgrade this soon, for me it really spoils an otherwise nice piece of equipment. The one thing that I would like more than any other and this is not just aimed at Sky-watcher, why don’t more companies do deluxe versions of their scopes. I am pleased with what I have bought even though some of it was given away, I would however be delighted with a better finder and better visual back. With an upgrade of these, the diagonal and eyepieces for say and extra 150 quid or there abouts maybe everyone would be happy.

Mak/Newt 190mm and 180mm Mak

I know that the two scopes are different and as such should not be compared with each other but as I have both I feel I should. If I could only have the one it would be the M/N 190, it is just that much more versatile with superb wide field views and almost as good high at power. I would normally not make such a comment but with having Televue eyepiece that will replicate similar powers on both feel I can.

If however you are an out and out planetary man or woman or are a keen doubles player this is a scope that should be strongly considered .

Clear skies,

Alan.

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I have the 180 pro, but these days i seem to have fallen out with it to a small extent, not saying its a bad scope, far from it, but it needs a heavy EQ mount and i much prefer the AZ4 mount these days, so the mak sits in its box waiting to come out, and only gets used a few times a year now

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I purchased a 180 mak in the autumn as I have always wanted a big apo but know I'll never be able to afford one!

Mine sits on a big pillar in an observatory so cool down isn't an issue.

First thing I did was give away the included accessories, get a standard SCT thread converter and fit a dual speed.

I'm a planetary and double star observer mainly and I have to say that it has really impressed. It must come very close to a big apo for a fraction of the cost. Yes, the included accessories are poor but the scope itself is very high quality I think.

I was touring a few nice doubles in bootes last night with a recently purchased 12mm radian an was treated to some cracking views.

Jupiter and Saturn recently blew my socks off frankly.

Alan, if you iron out the little creases then the 180s are very capable performers. It'll grow on you!

Regards, Chris.

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Thanks for sharing Alan - did you do any DSO viewing with this baby yet?

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Dunk,

No I haven't as it happens, I have to be in the mood for DSO. Of late I have spent so much time doing notes on the Pentax 5mm v the 4.5mm Delos and the same for the 14mm versions. I must take some time to just do a bit of sky surffing. This time of year I was always obsessed with bagging Antares, I wish I had a pound for ever minute I spent on that over the years. Anyway I nailed it the other week and again last night.

I want to try the M57 center star with the 12 inch again this year but with a BGO 9mm this time. Wouldn't mind some suggestions of DSO targets?

Alan.

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Any of the many nuanced objects in Scorpius or Sagittarius should make good use of your extra latitude Alan :) lots of fine detail to be discerned there, good test of light transmission etc

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Glad you are starting to use the 180 Mak/Cass Alan. I really like mine which I have had a few months. The views of Saturn and the Moon are brilliant. I agree the accessories are poor and as you know I bought the SCT converter so that I can use my SCT dielectric diagonal which is so much safer when I use my Ethos EPs.

Mark

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i also found the standard rear back to be poor, but i have added crayford focuser so this problem has gone away

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I did the very same thing , fitted the Revelation SCT focuser to mine and replaced the iffy diagonal .

Mine spends its days giving me superb close-up views/images of the Sun with a full aperture Baader filter.

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Seems as if I am not on my own when it comes to rebuilding the scope. It should really be better than it is. The optics themselves are very good and the other bits spoil the package.

Is it possible to buy a crayford for it that fits without this converter?

Alan.

Edited by alan potts

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If the optics are good, that's not a bad place to start, at least it can be upgraded. Upgrading the optics might be a bit more of a challenge! Not wanting to sound too flippant, but it's not like they're TV/APM/Tak money :eek:

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Good News ,

The new visual back has come and I can't wait ti see it, I sincerely hope it is a bit better quality than the one that is fitted.

Such a shame the optics are very good, I had it up to X270 last night and on Saturn and the Moon it was very sharp, even at around X200 on Antares it was showing a fairly tight disc and diffraction rings, no mean feat on a star only 21 degree above the horizon .

Alan

Edited by alan potts

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I see this post is years old, but i feel like blabbing anyway haha, i too have replaced all the cheap bits on my SW 150 Mak, i haven't felt the need for a crayford focuser since i have become quite good at using its focuser.I can say one thing though, regarding this 150, yes it's FOV is limited, yes they're not ideally suited for AP and deep sky, but if you accept it for what it does best (planetary/Lunar/doubles) then you won't be disappointed!.

Honestly, i have had some of the best planetary and lunar views i can remember with this 150, and i have had several scopes. The 150 is small enough to call grab and go, and boy does it reward you, given time to cool, and assuming you don't try to exceed its limitations. This is a niche scope, but what it can do it does brilliantly, I am impressed enough with this scope that i just may spring for the 180. I feel the 180 would be my permanent "never to be sold" scope cause frankly, short of a 7 inch frac which is ridiculous on many levels let alone price you can't beat Mak's on a price vs aperture vs performance level.

IMG_3716.jpg

Edited by Sunshine
typo's
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On 04/07/2013 at 15:51, alan potts said:

good few targets, mainly Saturn, Venus the Moon

2 years later...:-). I'm actually considering the mak 180 for planetary and bright DSO astrophotography. Is there anyone who has some experience with this? As for DSO's, I'm thinking bright globular clusters and galaxies which have a relatively small FoV. Together with my ZWO 178MC and ZWO1600MM, would this be a good combination to get decent quality images?

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1 hour ago, widotje said:

2 years later...:-). I'm actually considering the mak 180 for planetary and bright DSO astrophotography. Is there anyone who has some experience with this? As for DSO's, I'm thinking bright globular clusters and galaxies which have a relatively small FoV. Together with my ZWO 178MC and ZWO1600MM, would this be a good combination to get decent quality images?

I think that you will be better served with this scope instead:

https://www.teleskop-express.de/shop/product_info.php/info/p10753_TS-Optics-8--f-12-Cassegrain-telescope-203-2436-mm-OTA.html

A bit cheaper, more aperture, according to reports - very sharp and good for planetary visual (which means it will be good for imaging as well), a bit less focal length - better for wider fov. If you want even wider fov than with native resolution - I think you can utilize focal reducer as it has pretty decent flat field.

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Posted (edited)

Second the 8” Classical Cassegrain.

Loved my old Skymax 180 but my new 8” Cassegrain is much better. Will take far higher manification and is sharper with more contrast and better resolution and  is only slightly heavier than the 180. The stock Crayford is not bad at all but I replaced mine with a BaaderSteeltrack refractor focuser.One of the biggest advantages though is the freedom from dew. Never had any dew what so ever.

Well worth spending the extra. Also higher build quality.

B72441F4-C024-4E9A-A5D0-C439BB24D9D8.jpeg

Edited by johninderby
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According to Larry Carlino's review at Astromart, the GSO 8" Classic Cassegrain only has a working aperture of 7.34". 

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50 minutes ago, coopman827 said:

According to Larry Carlino's review at Astromart, the GSO 8" Classic Cassegrain only has a working aperture of 7.34". 

No, it's according to GSO rep who answered Larry's inquiry (via Agena Astro). To me that explanation simply does not make much sense - and it is question if person who offered such explanation really knows what it is all about.

Quote

The response was detailed and quite interesting.

The design of the telescope is a compromise that gives priority to high-power lunar and planetary performance.  With the relatively short-focus parabolic primary mirror, a large secondary that would degrade image contrast would not be desirable.  The solution: Use a smaller secondary [still a roughly 33% obstruction] and reduce the effective aperture of the scope to 7.34 inches(186.5mm).  According to the factory specs, the 100 percent illumination circle is 15mm. 

Just let us address one point in this reply - short focus parabolic mirror and size of secondary as means of stopping down scope.

For same mirror size, faster mirror (shorter focus) will require smaller secondary, not larger. Look at this image:

image.png.2d38d0d67652638ab1f49f3f30a23e5b.png

Shorter focus mirror will need less of secondary (intersection with line is shorter than that of long cone).

If there is point that has 100% illumination - that means no light is blocked at that point - there is no aperture stop before primary mirror (as it would affect whole field and no part of field would be at 100% illumination from light reaching front of scope aperture) - that means aperture stop needs to be after primary mirror - light is already bent at that point and any aperture stop will act as vignetting rather than smaller effective aperture. Just use eyepiece with field stop less than 15mm - and your scope should work as regular 8" scope without aperture stop as that part of field is 100% illuminated.

In any case - offered explanation in my view does not explain anything.

Much more plausible explanation would be that some sort of inferior mirror coatings was used.

Celestron uses Starbright XLT coatings for which they say reflects ~97% of the light. If GSO used coating of 89%, then for two mirrors of both systems we would have total transmission of:

0.97 * 0.97 = 0.94

and

0.89 * 0.89 = 0.7921

Ratio of the two is ~ x1.187

Now let's examine ratio of 8" vs 7.34" light gathering surfaces. 64 / 53.8756 = ~ x1.188

There you go - use inferior coatings and it will behave as if you used 7.34" instead of 8" aperture.

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Posted (edited)
On 08/01/2020 at 11:20, johninderby said:

Second the 8” Classical Cassegrain.

Loved my old Skymax 180 but my new 8” Cassegrain is much better. Will take far higher manification and is sharper with more contrast and better resolution and  is only slightly heavier than the 180. The stock Crayford is not bad at all but I replaced mine with a BaaderSteeltrack refractor focuser.One of the biggest advantages though is the freedom from dew. Never had any dew what so ever.

Well worth spending the extra. Also higher build quality.

B72441F4-C024-4E9A-A5D0-C439BB24D9D8.jpeg

That's very interesting John. I've always fancied a classical Cass'. Your's looks quite short in physical length, so could I ask what F ratio it is? In the past they tended to be in the F20 + ratio, which would suit me fine. And even if it is less than 8" working aperture, although as D determines resolution so it should act as a full 8", its still aperture enough to pack a very serious planetary punch, I'm certain. 

The central obstruction and primary hole would be virtually negligible in reducing brightness & contrast.

The diagram above, showing the light path makes no sense to me, as the secondary cone doesn't cross the primary at all. Weird!!

 

Edited by mikeDnight

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Posted (edited)

It is F12 so not a huge difference to the mak or 8” SCT..Nearly the same weight and not alot bigger than the 180 mak so just  as easy to mount..I fitted tube rings so I could mount the dovetail on the “side” for easier fitting to the Alt-az mount

It just impresses me every time out so I don’t get too caught up in the specs. I simply enjoy using it. . 👍🏻👍🏻👍🏻

0B0CCC5B-A47D-4DA7-B205-F27F7E31A59A.jpeg

Edited by johninderby
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Quote

 

The specs for the 8" Cass. at agenaastro say that the reflectivity of both mirrors is greater than 96%, which is very good.

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8 hours ago, coopman827 said:

The specs for the 8" Cass. at agenaastro say that the reflectivity of both mirrors is greater than 96%, which is very good.

TS one is quoted to have 99% dielectric coatings ...

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13 hours ago, johninderby said:

And the Skymax 180 is actually the Skymax 170.

 

I think you'll find John that modern 180s with o/sized mirrors are actually 180 or very close. I've measured mine at 179mm and others in reviews have found the same.

Chris

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