201 replies to this topic

[astroneil]

Here, I wish continue the work I started on another forum in July through August 2014. It concerns the field performance of an Orion 180mm f/15 Maksutov cassegrain ( known affectionately as 'Cornelia'). For reference see here:-

 

http://www.cloudynig...tural-exchange/

 

As an experienced tester of telescope optics, I am still of the opinion that a large maksutov such as this makes an excellent alternative to a top-rated medium aperture apochromatic refractor, because of its optical quality, ultra-portability and lack of maintenance. It also makes much better economic sense. Some folk have expressed concerns about whether an instrument like this might exhibit abnormal thermal issues. One purpose of this work is to establish whether that is true or not.

 

My methodology remains the same; I begin by testing the maksutov against a fully acclimated 5" f/12 classical achromat.

 

Here are some of my most recent observations.

 

 

Date: 06.09.14
Time: 2200h
Ambient; 9C, 1016mB, rising. Nice clear sky. Seeing fair to good. Very autumnal; cold.
Instrument: 180mm Orion Mak.
Enjoyed my first glimpse of the vast lunar regolith this evening but at an altitude that was far from ideal. The 32mm Plossl, which offers the widest true field so far as I know for this telescope, couldn’t quite fit the entire Moon into the field of view. Still the image was intensely bright, the ray craters prominent and the eastern lunar limb crisply laden with impact craters. 
Drank up some beautiful sights after visiting a suite of colourful double stars from the comfort of my back garden: Albireo, Mizar, Iota Cassiopeiae, Almach, 61 Cygni, Iota Trianguli, Eta Persei, Zeta Lyrae, Gamma Delphini. Beautiful stable images throughout the evening at 113x. Packed up at 00:30h (7th), final temperature 6.0C. No obvious thermal problems encountered.

 

 

Date: 07.09.14
Time: 21:00h
Ambient: 10C, 1018mB, rising, fully clear sky, almost a carbon copy of last night, save for a twist in the seeing conditions later in the vigil.
Once taken out of the shed, the Maksutov took a wee while to deliver its best images. Temperatures fell a bit more rapidly this evening, reaching 8C by 22:06h. Still the images of Delta Cygni were excellent from about 21:40h, so no big deal. Seeing deteriorated approaching midnight and it became much more difficult to see its companion. Fainter pairs like Iota Cass showed the same behaviour; still recognisable as a triple but noticeably degraded. That said, the instrument continued to be eminently useable at lower powers right from the get go, and I enjoyed visiting some more bright wide doubles with a full moon (or very nearly so) low in the south.
Final temperature at local midnight: 6C.

 

Thanks,

 

Neil.

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Edited by astroneil, 08 September 2014 - 12:02 PM.

[Ed Holland]

Neil,

 

Excellent reports - well detailed with the temperature and atmospheric information. Excellent methodology to compare against the well known optics of the 5" Achromat.

 

This really is prompting me to do a scaled down version of this evaluation: To compare the Orion 127mm and the Celestron 102mm f/10 bargain scope.

 

I look forward to an informative and interesting thread.

 

Cheers,

Ed

[ggalilei]

It would be good to have an idea of the humidity levels (did I miss seeing that information?).

[astroneil]

Thank you gents.

 

I can also include humidity levels from my local weather station too. No problem.

 

Cheers,

 

Neil.

[Asbytec]

Neil, you're obviously bitten by the MCT bug. There is no cure.

 

Let these observations in a pretty stock 150MCT in good seeing, cooled and collimated, speak for themselves illustrating my own pleasure observing through this instrument in this climate.

 

 

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[Asbytec]

Two more...

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[ChristianG]

Hi.

 

Great report! I did some 'evaluation' on mine, after buying it on a certain auction site for 800$ and having shiped from California all the way up here in Canada! Collimation was spot on when received, see below: my attempt at recording the star test with an artificial star about 30 meters away indoors. Theory says that for green light 500 nm, the diameter of the dark ring should be 8.3 pixels of the Neximage 5 camera I used, and that's what can be seen on the photo: somewhere between 8 and 9 pixels diameter (I upsampled the photo 8X so that the pixels can be seen).

 

It is a really good instrument, and because the primary baffle can have a decent opening diameter, they took some measures to reduce the usual reflections found in smaller Synta-made Maksutovs (search for 'MCT baffle mod' in the forums). So contrast is very good stock.

 

I now have it on an HEQ5 mount. If only I had time to go a dark site, my balcony isn't good enough--too much vibrations for the 2.7 m focal length... Cheers!

 

--Christian

 

[Bomber Bob]

Thanks y'all for your research and reports.  Gives us refractor folks something to think about.

[Ed Holland]

Norme - wonderful illustrations - than you for posting them!

 

It's been full moon here, with a side order of high thin cloud.... a bit like peering at the neighbours through net curtains . Later on we were served a main course of thick cloud . Seeing was excellent though, so I was able to pick out lots of detail in the tiny wisps of moisture within these magnificent, bright extended objects.

[Starman1]

When a Mak works, it's a wonderful thing.

I have the Synta-made 121mm Maksutov (called 127, but it really isn't), and the images are so good that, after 11 years, I have no intention of selling it.

One of these days, I may get one of the 150mm Synta Maks and an iOptron 150mm Mak and do some comparisons.

I have the mount and the eyepieces.  All I need are the OTAs.

 

[Oh, honey!  I really need to do this comparison for Cloudy Nights........... ]

[Asbytec]

It's been full moon here...

 

 

Here, too.

 

Monsoon season to boot, one more month or so then dry season if it comes early this year. Ed, thank you. I simply want to illustrate having the time of my life with this Mak. You know, I am sure it's not a premium optic and it's not that other scopes cannot compare, but there is something nice about a Mak. It may just be the good tropical seeing that makes all the difference. But, it does not change the fact I am really enjoying observing as Astroneil talks about, it just happens to be through a Mak. 

Edited by Asbytec, 09 September 2014 - 07:25 PM.

[Ed Holland]

Norme, as you no doubt spottet, my "full Moon here" statement was meant to be silly  

 

Don, you were lucky to get 121mm, I only got 118mm, but it is still a neat package.

 

Any telescope that works for the observer is a good telescope. We can debate star tests, central obstructions and aberrations all day, and they certainly have their place in our understanding what determines optical performance. However this can be worried to excess and frequently it is good to step back, use the instrument and try realise its capabilities, not its shortcomings. Had Galileo Gallilei spent months fretting about the undercorrection and CA in his optics we'd still believe the Sun went around the Earth 

 

Ed

[Bomber Bob]

I may get one of the 150mm Synta Maks and an iOptron 150mm Mak and do some comparisons.

 

Don, maybe you could get a Federal Grant?  I'd be interested in your assessment.

[Asbytec]

Bomber, with a federal grant, I'd have a whole assortment of 6 to 10" Maks...for serious study and research, of course.

[Ed Holland]

Clouds again here, so the 4" to 5" "Mak 'n Frac double-trouble double observing session will have to wait.

 

In other news, I'm now searching (longingly, yet in vain) for a bargain large Maksutov. Purchase will have to wait, yesterday I bought some much needed parts for the MG, and also paid the car registrations.....

 

Perhaps I'll stick with the budget gear after all.

[astroneil]

Evening all,

 

Thanks for chiming in. Great stuff.

 

 

Date: 10.09.14
Time 22:00h
Ambient: 13C, 1028mB, rising, 80% humidity, quite hazy, transparency poor.

My students are now back and my shed also doubles up as my office. I was teaching this evening in there and had the heater on for a while. Cornelia was taken out of this environment (temperature 18C) and left to cool off for about 40 minutes (so ~5C drop). The refractor showed that the seeing was very good, as judged by examining the high magnification images of some tough test doubles. The same was true with the large Mak. Wonderful images of Delta Cygni at 340x.

Swung the ‘scopes eastward to Lambda Cygni. The significant drop in transparency had a material effect on the images garnered in both telescopes. I failed to see it at all in the 5-inch glass and had to look quite hard to find it in the Maksutov but after a few prolonged moments studying the diffraction images, I was able to finally pick it off. To get the best double star images you need good seeing and good transparency.

Even on this fine evening, it is easy to discern that the 7 inch Maksutov is more sensitive to seeing than the smaller aperture refractor. I became especially aware of this when I pushed the magnification in both telescopes. Attaching the dedicated Baader 2.25x Barlow to the click stop zoom, I was able to crank the power up to 759x in the Mak and turned the instrument on Delta Cygni very high in my sky. The diffraction rings of the close pair were a bit distorted, being concentrated in three loci. The image was almost identical to that reproduced in Fig 2-3 on page 24 of Richard Suiter’s ‘Star Testing Astronomical Telescopes’ ( first edition). This he attributes to atmospheric turbulence. The refractor image at 429X (the highest I could go with the setup) was less distorted in this capacity, the fainter diffraction rings remaining fairly circular.

 

Still, when I turned the instruments on Mu Cygni and returned to more ‘normal powers’, the Maksutov strutted its stuff, revealing the close in yellow A/B pair more readily than the refractor. 340x is a great place to be with the big Mak! The C and D components, both wide away, were beautifully framed at this high power and the fainter C star easier to see with the larger aperture.

The Moon was rising big and bright when I packed in. Will leave that for another night.

A most enjoyable evening with two fine instruments!

 

Final temperature 11.5C at 23:45h.

 

Thanks,

 

Neil.

[astroneil]

Hi Norme,

 

Thanks for posting all those drawings; they are very beautiful.  I very much enjoy sketching planets too, especially Jupiter, but mine are nowhere near the quality of yours.

 

My 5 inch glass produced some fine details, but I fear the details that the 7-inch Maksutov can reveal will easily overwhelm it.

 

I am thoroughly enjoying the versatility of my Baader zoom. Fantastic value for money! I think quite a bit of the discussions about eyepieces - especially premium models - amount to little more than poppycock. Not missing my Delos one little bit.

 

The weather is set fair for another few days and I will dedicate some time to viewing the waning Moon with the Maksutov. I am very excited about the prospect.

 

Cheers

 

Neil.

Edited by astroneil, 11 September 2014 - 06:49 AM.

[Jon Isaacs]

Neil:

 

I just wanted to thank you for posting your observations.  I particularly benefited last night, with a Hurricane down south, the sky was partially blocked by clouds but Cygnus was clear and I had never seen Mu Cygni before.  I was able to split it in my 4 inch F/5.4 TV but it was not an easy, obvious split, it required care. Sky Tools lists it at 1.56 arc-seconds at magnitudes 4.5 and 6.3.  I also had out my 13.1 inch F/5.5 Starsplitter Dob and it lived up to it's name, splitting it very cleanly and very wide. I was using about 300x in both scopes.  This season, I have been observing Lambda Cygni, at 0.92 arc-seconds, I don't bother with the 4 inch but the Starsplitter split it nicely last night, visible as a split at about 230x but much better at 600x. 

 

Part of what your evaluation is showing is the importance of aperture when observing closer doubles.  It is consistent with my experiences and this seems to be an area where the theory and the practice are very much in agreement.  With wildly unequal doubles, there can be value in an unobstructed scope but for reasonable doubles like these two, a relatively small difference in aperture can be the difference between making the split and not making the split.  52 Orionis is a good example. At 1.0 arc-seconds (though some report it slightly wider) and magnitudes 5.3-6.1 it is just beyond the reach of a 4 inch but doable with a 5 inch. The result being that I have not made the split in my 4 inch apo but have been able to make it with a Skywatcher 130mm F/5 Newtonian.. 

 

I also want to thank Norme for his drawings, I sure wish I could draw.. My attempts have been frustrating and disappointing but maybe I should start again with double stars as they are about the simplest, though that makes capturing the subtleties all the more important. 

 

Jon

[Starman1]

Gentlemen,

 

52 Cygni is a double also, separation 6.1" (easy), magnitudes 4.2 and 9.5 (nice dichotomy).

The main star is 206 ly away, giving you some idea of the distance to the Veil Nebula.

It is a G9.5 star (sometimes called K0), so somewhat orange.

It's about 106X as luminous as the sun and 15.3X the radius, so it's a big, bright, star.

 

Mu Cygni is a multiple star (5 components):

A--4.69, F6

B--6.12 G2 separation 1.9" (2004), and 1.6" (2012), so 1.56" sounds right for 2014.

C--11.5 F6 separation 72.6" (1999)

D--6.9 F2 separation 197.5" (2011)

E--13.3 A5 separation from D is 16.9" (1999)

 

Obviously AB is the double we normally see.  The separation is decent, and the magnitudes are similar, and the colors similar.

[Jon Isaacs]

Gentlemen,

 

52 Cygni is a double also, separation 6.1" (easy), magnitudes 4.2 and 9.5 (nice dichotomy).

The main star is 206 ly away, giving you some idea of the distance to the Veil Nebula.

It is a G9.5 star (sometimes called K0), so somewhat orange.

It's about 106X as luminous as the sun and 15.3X the radius, so it's a big, bright, star.

 

Mu Cygni is a multiple star (5 components):

A--4.69, F6

B--6.12 G2 separation 1.9" (2004), and 1.6" (2012), so 1.56" sounds right for 2014.

C--11.5 F6 separation 72.6" (1999)

D--6.9 F2 separation 197.5" (2011)

E--13.3 A5 separation from D is 16.9" (1999)

 

Obviously AB is the double we normally see.  The separation is decent, and the magnitudes are similar, and the colors similar.

 

Don:

 

I use Skytools 3 which uses the orbital data to compute the separations so the 1.56 arc-seconds should be quite accurate.  52 Cygni is relatively straightforward and enjoyable but just to be clear, the double I referred to is 52 Orionis which is listed by Skytools 3 as having a separation of 1.0 arc-seconds though I have seen discussion that it is closer to 1.1 arc-seconds. It just happens to be a star I use to gauge the seeing and so I have quite a bit of anecdotal data on it.  

 

Jon

[Starman1]

Jon,

Some othrs for testing seeing:

32 Orionis 1.1"

Struve 228 1.1"

Struve 577 1.1"

36 Andromedae 0.8"

7 Tauri 0.66" (did this in an 8" SCT)

Zeta Cancri  0.61"

ADS 5290 0.6"

Lambda Cassiopeiae 0.57"

My list goes down to 0.2", but very few observers see below about 0.6-0.7"

 

Close with beautiful colors (some of my favorites):

alpha Piscium 1.9"

iota Leonis 1.5"

lambda Ophiuchi 1.5"

70 Ophiuchi 1.6"

pi Aquilae  1.4"

 

Of course, there are tons more (like 52 Orionis).

 

I'm not a double star specialist, but I've seen my fair share.

[Jon Isaacs]

Jon,

Some othrs for testing seeing:

32 Orionis 1.1"

Struve 228 1.1"

Struve 577 1.1"

36 Andromedae 0.8"

7 Tauri 0.66" (did this in an 8" SCT)

Zeta Cancri  0.61"

ADS 5290 0.6"

Lambda Cassiopeiae 0.57"

My list goes down to 0.2", but very few observers see below about 0.6-0.7"

 

Close with beautiful colors (some of my favorites):

alpha Piscium 1.9"

iota Leonis 1.5"

lambda Ophiuchi 1.5"

70 Ophiuchi 1.6"

pi Aquilae  1.4"

 

Of course, there are tons more (like 52 Orionis).

 

I'm not a double star specialist, but I've seen my fair share.

 

 

Those are some nice ones, lambda Ophiuchi is at 1.46 right now and I enjoy it most every night..  I use Skytools 3 because it calculates the orbits of short period binaries.  For example zeta Cancri is currently listed at 1.12 arc-seconds, in 2000 it was listed at 0.83 arc-seconds.  I enjoy doubles, some nights I just check out my old friends, some nights I make new friends.  Neil's mu Cygni is a new friend.  possibly doable in an 80mm but it would be tough-tough, unequal and nearly at the Dawes limit.   

 

Jon

[ggalilei]

Good suggestion, Jon, to try mu Cygni in 80mm. I just did and in fact it can be split nicely, barely but nicely. SV80ST triplet and 2-4mm Nagler at 2mm for 240x. The secondary was clearly visible almost attached to the primary, at the right PA (>300). I apologize for straying from the original topic.

[Asbytec]

Neil, Jon, okay enough with the flattery already. 

 

Thank you, sketching is just a way of sharing with others the excitement of observing alone. Sometimes when I see something amazing, just gotta share it with those who understand the excitement we feel. It's not unlike the enjoyment Neil expresses in his threads of late.

 

I guess I am a MCT affectionado, and could just as easily be a SCT, Newt, or refractor nut, as well. But the MCT in this environment is just very performing and pleasing. That's what I want to share, with Neil and others, in keeping with the spirit of the topic. 

 

Thank you...

[astroneil]

Good suggestion, Jon, to try mu Cygni in 80mm. I just did and in fact it can be split nicely, barely but nicely. SV80ST triplet and 2-4mm Nagler at 2mm for 240x. The secondary was clearly visible almost attached to the primary, at the right PA (>300). I apologize for straying from the original topic.

Hi Antonino;

 

Yep it's just doable with an 80mm refractor alright. But it was not offered as a test. It's so very pretty that's all.

 

No problem in an 80mm achromat.

 

http://neilenglish.n...s-blog-part-ii/

 

Heck, that's another guidin fur Gaius, my bonnie 80mm f/5 achromat.

 

Regards,

 

Neil.

Edited by astroneil, 12 September 2014 - 05:39 PM.