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bluesilver

maksutov cassegrain compared to Refractors

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Thanks for your comments John.

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.

I hadn't forgotten or overlooked the aperture factor John.  Whilst what you say is correct if the seeing supports the better resolution, but often it doesn't (at least where I live!).  Also I would have to carry the Mak outside to use and taking into account I often observe at short or no notice it wouldn't have time to reach thermal equilibrium very often.  I know this as I have owned more than one!  Though in theory it's better,  the way I observe, the conditions I have,  the focal length factor of the Mak and what I want to observe the 120ED is far better for me than the big Mak ever was.  Looking at my observing diaries it's clear I observed more often and to better effect than I ever did when I used the big Mak.     A no brainer for my needs.    Each to his own.

 

 

 

 

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The relationship between aperture and seeing might be worth repeating to aid this discussion.  When the aperture is smaller than the typical size of the turbulence cells in the atmosphere the light tends to pass through one cell at a time causing the image to sift location but remin reasonably coherent. When the aperture is much larger than the typical turbulence cell the image shift less but breaks up incoherently as it passes through multiple cells.

While it varies the typical transition aperture is 300mm so stopping down to below 300mm shifts you from one regime to the other.

Regards Andrew 

Edited by andrew s
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Yes so much is dependant on your typical local seeing conditions. So it’s a case of whart scope suits your location.

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Just to throw in a wrench or two ... :D

Since OP almost decided to go for Mak180, I'm wondering if this could be something worth considering:

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

As far as I know, Australia has a dealer of GSO equipment as well, so worth checking there for availability as it would certainly be more affordable then shipping it half way across the globe.

Quick comparison:

200mm vs 180mm - more resolution and sharper image at lower magnifications (given same optical quality).
Price about the same - slight edge for 8" Cass in TS pricing.
Slight weight advantage for 8" Cass (7.5 vs 7.8kg).
Much less of a dew magnet since no front corrector plate.
Cool down time is consequently less in 8" Cass
Probably better focuser as it has 10:1 reduction and does not cause mirror shift when focusing.
CO size - Mak180 probably wins - I've seen figures around 30% quoted online - 33% for 8" Cass
F/ratio and focal length - again +Mak180 as it is F/15 vs F/12 and 300mm additional FL - easier on EPs, easier to reach high magnifications.
8" Cass - diffraction spikes - might detract some people, better baffling of the tube - probably very small boost in contrast because of this.
 

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6 hours ago, dweller25 said:

@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.

Sadly, it looks like a lot of the Russian stuff will become increasingly hard to get hold of.

Post below from a year ago by vendor Markus Ludes with regard to the demise of Intes Micro in particular.

It seems a lot of the opticians who worked for the likes of Intes , Intes Micro, STF, Lomo, Yelena and the like have either retired, or are primarily working on military type applications.

LZOS APO's are also becoming a rarity with only very limited production runs for 'off the shelf' type scopes. Which is why i've got my name down on the list for one before they disappear too.

 

https://www.cloudynights.com/topic/623980-maksutov-telescopes-future/#entry8679000

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You can hardly blame them, they make optical instruments for a living and military or similar customers can pay more for the product than amateur astronomers usually can. I occasionally made equipment for the MOD and associated firms, they happily paid much more for items that I usually made for amateurs.   😀

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16 minutes ago, Peter Drew said:

You can hardly blame them, they make optical instruments for a living and military or similar customers can pay more for the product than amateur astronomers usually can. I occasionally made equipment for the MOD and associated firms, they happily paid much more for items that I usually made for amateurs.   😀

Reminded me that NASA was given two spare Hubble class mirrors by the US military.  Although they might have a tendency to point the wrong way.

Now if anyone has a spare...

Regards Andrew 

Edited by andrew s

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4 hours ago, andrew s said:

Reminded me that NASA was given two spare Hubble class mirrors by the US military.  Although they might have a tendency to point the wrong way.

Now if anyone has a spare...

Regards Andrew 

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.

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Does this make you wish the UK had a constellation of spy satellites with lots of spare mirrors?

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One thing I noticed about my 127mm Mak is that if you defocus a star, there's a black hole in the center of the light disk due to the central obstruction.  As I bring the star into focus, the hole gets smaller and smaller, but at best focus, it seems to be preventing all of the light energy from being focused to a pinpoint.  The star just won't collapse into a perfect pinpoint.  In fact, the focused star seems to twinkle, possibly due to thermal acclimation issues.  It reminds me of the black hole trying to push out all the light crowding in on it.  I'd swear I can still see glimpses of a tiny black pinpoint in the center of the star at best focus.

I then tried the same experiment with my co-mounted AT72ED.  A star defocuses to a perfect disk all the way to the center.  Then, as the star is brought to focus, it just goes down to a tiny pinpoint without any fuss.  There is no twinkle, either.  Perhaps due to better thermal acclimation.

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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 0.985 - just a smidge short of optical perfection and 1/9.5 wave mirrors. The moon in this thing is absolutely awesome and ridiculous. It will outperform larger SCT’s on finer rendered detail - what is visible in the Intes will be blurs in larger commercial scopes of less optical quality. So aperture sometimes does not rule. Quality over quantity. Its alright getting the light into your scope it’s how the optics “massage” it when it’s in there what matters.

 

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26 minutes ago, dave armeson said:

imageproxy.php?img=&key=127fb0a7147957bfMy 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 0.985 - just a smidge short of optical perfection and 1/9.5 wave mirrors. The moon in this thing is absolutely awesome and ridiculous. It will outperform larger SCT’s on finer rendered detail - what is visible in the Intes will be blurs in larger commercial scopes of less optical quality. So aperture sometimes does not rule. Quality over quantity. Its alright getting the light into your scope it’s how the optics “massage” it when it’s in there what matters.

 

Fabulous scope the Intes Micro 815 Dave. I think they are available to special order only now, is that correct ?

The last time I saw one for sale new it was around £4,000 for the optical tube.

How does the somewhat more affordable and available Skywatcher 180 Mak-cassegain compare out of interest ?

 

 

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Posted (edited)

I had a Mak 180 pro before this. Great scope but the Intes Annihilates it, unfortunately 😂

Intes ceased production last year.

Edited by dave armeson
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11 minutes ago, dave armeson said:

I had a Mak 180 pro before this. Great scope but the Intes Annihilates it, unfortunately 😂

Intes ceased production last year.

Thanks Dave. Out of interest have you compared the performance of the Intes Micro 815 with a top shelf 6 inch apo refractor ?

 

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On 04/09/2019 at 10:55, 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.    😕

I'm sure that's true Peter. Probably one reason I like my 4" so much, my seeing is often poor, yet I have seen the Cassini Division with it a few times this year.

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Interesting comment Peter. One night a few weeks back, I set up my 180 Mak, 102mm f13 frac and an ED80 side by side on an area of grass and watched Saturn for an hour to test out the hypothesis about smaller scopes sometimes giving more detail with poorer seeing. Despite the slightly better contrast in the fracs, the detail in the 180 Mak was noticeably better; Cassini was clear in all three but much finer and darker in the Mak. To be fair, I've found an improvement in performance with the 180 Mak since insulating it - it gives excellent performance now most of the time, whereas without insulation, it was some of the time.

Chris

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20 minutes ago, chiltonstar said:

Interesting comment Peter. One night a few weeks back, I set up my 180 Mak, 102mm f13 frac and an ED80 side by side on an area of grass and watched Saturn for an hour to test out the hypothesis about smaller scopes sometimes giving more detail with poorer seeing. Despite the slightly better contrast in the fracs, the detail in the 180 Mak was noticeably better; Cassini was clear in all three but much finer and darker in the Mak. To be fair, I've found an improvement in performance with the 180 Mak since insulating it - it gives excellent performance now most of the time, whereas without insulation, it was some of the time.

Chris

What is your insulation material and  set up, I've been thinking of insulating my Mak.

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7 hours ago, Paz said:

What is your insulation material and  set up, I've been thinking of insulating my Mak.

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:-

Chris

makinssmalla.png

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I have been comparing my SW 127 Mak against my recently acquired WO Zenithstar 102mm doublet. So far I have not seen much of a difference in performance. I love the wide field of view with the refractor and it is very sharp but the MAK shows more lunar detail and doesn't need a barlow to get a decent magnification (F7 and not F9 doublet).

If you are based in Sydney or are in the city at some point , pop into Bintel in Glebe and have a look at the instruments and their mountings. I believe the 180 Mak is quite heavy.

 

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47 minutes ago, chiltonstar said:

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:-

Chris

makinssmalla.png

That looks great - it does look like the hubble-on-a-tripod, or like a suspiciously rotund moonraker scope! 

I'm sure I've got some insulation roll somewhere, I'm going to give it a go.

Also I like the raci and rigel finder arrangement!

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1 hour ago, chiltonstar said:

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:-

Chris

makinssmalla.png

I like that RACI + Rigel finder combination as well, how does it work? special adaptor on the bottom of the Rigel to accommodate the RACI?

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3 hours ago, jock1958 said:

I like that RACI + Rigel finder combination as well, how does it work? special adaptor on the bottom of the Rigel to accommodate the RACI?

Nothing clever. I filed the base of the Rigel to fit the barrel of the RACI and attached it with a couple of cable ties.

Chris

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On 04/09/2019 at 22:03, Louis D said:

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.

spacer.png

spacer.png

Does this make you wish the UK had a constellation of spy satellites with lots of spare mirrors?

nice picture there!

 

This could be of topic, but I wonder how you clean such a big a mirror?

 

Clear Skies

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The problem for me with the Orion sw 180 maks are

Both have the vixen rail on the inside thinner part of the sct instead of the thicher cast part of the front and rear part of the sct. I dont trust that thin part to hold a 22 lbs scope.

Both dont have any venting or air holes making cooldown time 3 hrs for this size.

Someone said 30 min for the 127 mak which is alot smaller but I bet even that wasn't good enough cooldown. Only acceptable.

The first generation models of sw ones back in 06 or 08 if I remember didnt have a true 2 inch visual back like a 8 inch sct. It was abit smaller like the 5 or 6 inch sct

I'm not sure I would buy either 

Joejaguar 

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