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curiosidad
sage


Reged: 06/09/11

There is the telescope "perfect" for the Moon?
      #5784298 - 04/07/13 04:55 PM

Hello,
It is often said that to observe the moon, almost any telescope goes well.
But, in his opinion there is some model above the rest to be a little better for lunar observation?
From what aperture lunar observation becomes interesting, detailed and serious observation?
greetings


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THEPLOUGH
ELEVEN Grandchildren; FIVE Ducklings
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Reged: 01/11/08

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Re: There is the telescope "perfect" for the Moon? new [Re: curiosidad]
      #5784504 - 04/07/13 06:38 PM

Well my 8" gives a very good view especially when used with the 13mm EP... I also have a 3" refractor that is half decent, but the bigger the better rule must also apply...

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buddyjesus
Carpal Tunnel
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Reged: 07/07/10

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Re: There is the telescope "perfect" for the Moon? new [Re: THEPLOUGH]
      #5785063 - 04/07/13 11:40 PM

I agree with the above because you want to get over 100x to get good visualization of finer detail and to dim the image. I think a 4" is considerably better than a 3" for the moon because my 3" reflector maxed out about 75x. Moral of the story, if you get an 80mm, make sure it is an apo or long focal length achromat, not a modest widefield budget reflector.

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Eric63
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Reged: 06/16/12

Loc: Ottawa, Ontario
Re: There is the telescope "perfect" for the Moon? new [Re: buddyjesus]
      #5785116 - 04/08/13 12:16 AM

Now this is where my 127mm Mak shines! Just amazing on the moon.
Eric


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Astrojensen
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Reged: 10/05/08

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Re: There is the telescope "perfect" for the Moon? new [Re: curiosidad]
      #5785264 - 04/08/13 03:59 AM

Quote:

From what aperture lunar observation becomes interesting, detailed and serious observation?




That is mostly dependent on the observer's skill and enthusiasm. For me, a 60mm of high quality does the job. I know I've seen many things with my 63mm Zeiss that other people have missed, but that is also because I've been studying the Moon for more than twenty years and know what to look for, when to look for it and how to look for it. And many of those details weren't easy to see, but that made it all so more rewarding to finally see them.

My 85mm apochromat is a very clear step up from the 60mm, but a 100mm is a bigger step, but doesn't feel much bigger than the 85mm, oddly enough. It's as if the 85mm is much more than halfway to the 100mm from the 60mm. But a 125mm is a huge leap up from a 100mm and leave the 85mm in the dust.

Today I often use a 150mm f/8 achromat, stopped down to 125mm f/9.6, equipped with a Baader Maxbright binoviewer and 25mm Zeiss eyepieces. Lunar views are extremely good, with very short cooldown time, so that I can be observing quickly. There is a ton of things to see with a 125mm, enough for a lifetime.

But if I didn't have any of the bigger scopes, I would still be observing the Moon with my 60mm scope and enjoy it.


Clear skies!
Thomas, Denmark


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azure1961p
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Reged: 01/17/09

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Re: There is the telescope "perfect" for the Moon? new [Re: Astrojensen]
      #5785316 - 04/08/13 06:24 AM

Thomas what about the C8 and 12" reflector.

Pete


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Astrojensen
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Re: There is the telescope "perfect" for the Moon? new [Re: azure1961p]
      #5786151 - 04/08/13 02:29 PM

Quote:

Thomas what about the C8 and 12" reflector.




I've sold the C8 back to its original owner, as I didn't use it. The 12" reflector does give fantastic images at up to 160x, but then its astigmatism and spherical aberration starts to get really noticeable. It should be a formidable lunar telescope if it wasn't for the astigmatism and overcorrection. Heck, it still outperforms the 5" refractor, but not as much as doubling the aperture would suggest. Thermal issues are less than in the C8, so the potential to outperform the C8, if not for the optical issues, are certainly there. The C8 was only marginally better than the refractor on most nights and was hysterically sensitive to collimation and focusing, far more so than the newtonian. The newtonian is the easiest scope to collimate I've ever owned, now that I have a laser.


Clear skies!
Thomas, Denmark


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mikewirths
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Reged: 06/16/08

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Re: There is the telescope "perfect" for the Moon? new [Re: Astrojensen]
      #5786290 - 04/08/13 04:02 PM

If I had to "start over" and buy a new scope I would go for a Starstructure dob (driven) with Carl Zambuto optics. I have had a lot of scopes including a beautiful 5" AP superplanetary but nothing beats the contrast and detail of a fine large (16-18") optic in a premium dob IMO.

I have had jaw-dropping views of the moon during great seeing at high magnifications (600X's and up) in my 18" Starmaster, on the Jovian moons Ihave had fleeting glimpses of detail!

I would get one of these if I had the money:

http://www.starstructure.com/starstructure3_003.htm

cheers

Mike


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azure1961p
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Re: There is the telescope "perfect" for the Moon? new [Re: mikewirths]
      #5786640 - 04/08/13 06:58 PM

Thomas I had a C8 like that. Gross astigmatism and SA in the mix too. It was an utter shame as mechanically it was a beautiful Celestron. The awful awful views of stars at 270x was wrenching - astigmatism on the verge of wedging. Looking back on it I wonder if it was just an offcenter corrector. I sold it though. It still bugs me because it was so robust but what's it worth if I can't get past 175x without issues. It was Celestrons CLASSIC C8 - bought in the midst of Halley Hoopla.

When I read a review of competing telescope mirrors in the 10" size in Sky and Tel and PARKS walked off with the prize, it was my intention at that point to get a mirror quoted as having "essentially perfect star images". What made it so painful was some folks saying a special night was needed to see diffraction patterns and it wasn't as readily coming as one might expect. I was naive about diffraction so I tried but I knew all along great seeing wouldn't unsquish an astigmatic star image.

Oh the crime that followed - so I finally get the 10" PARKS just a month or so after Mount Pinatubo killed deepsky transparency!!!!! I couldn't see M51s arms, rifts in M31 not M33s arms.

I was losing even when I was winning. Lol it was a frustrating time.

Are you going to have it re figured? Might be better to get a new GSO mirror?

Pete


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Astrojensen
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Re: There is the telescope "perfect" for the Moon? new [Re: azure1961p]
      #5787307 - 04/09/13 02:53 AM

Sorry to hear about your lousy C8. Mine had fantastic optics, but that was moot, as the tube currents never settled in the carbon fiber tube (carbon fiber has TERRIBLE thermal properties for closed tube telescopes).

I was actually thinking about letting Carl Zambuto work his magic on the 12" mirror, but he has stopped refiguring of cheap mirrors and I couldn't afford it anyway. Replacing the mirror with another GSO one seems to be the way to go. Teleskop Service in Germany sells certified mirrors with the same focal length and diameter as the one in this scope, but they are a little pricey. I'll need to save up for one, as I can't afford one right now.

And then I find myself still dreaming about a large refractor... A 7" - 8" f/12 would be soooo nice! I am very tempted to get an ISTAR lens and build a large Richard Berry mount for it, now that I have experience with dobsonians and has seen how smooth and stable they can be. There is no question that a refractor would be far superior, aperture for aperture, in my climate.


Clear skies!
Thomas, Denmark


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Tom and Beth
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Reged: 01/08/07

Loc: Tucson, AZ
Re: There is the telescope "perfect" for the Moon? new [Re: Astrojensen]
      #5805352 - 04/17/13 07:53 PM

Quote:

Sorry to hear about your lousy C8. Mine had fantastic optics, but that was moot, as the tube currents never settled in the carbon fiber tube (carbon fiber has TERRIBLE thermal properties for closed tube telescopes).

I was actually thinking about letting Carl Zambuto work his magic on the 12" mirror, but he has stopped refiguring of cheap mirrors and I couldn't afford it anyway. Replacing the mirror with another GSO one seems to be the way to go. Teleskop Service in Germany sells certified mirrors with the same focal length and diameter as the one in this scope, but they are a little pricey. I'll need to save up for one, as I can't afford one right now.

And then I find myself still dreaming about a large refractor... A 7" - 8" f/12 would be soooo nice! I am very tempted to get an ISTAR lens and build a large Richard Berry mount for it, now that I have experience with dobsonians and has seen how smooth and stable they can be. There is no question that a refractor would be far superior, aperture for aperture, in my climate.


Clear skies!
Thomas, Denmark




Anyway you could be convinced to take that mirror and polish it towards perfection? I realize it's a bit large for a first project, but with all the help available on the web, plus maybe a bit of hands on help to grasp the Foucault test....


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Astrojensen
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Re: There is the telescope "perfect" for the Moon? new [Re: Tom and Beth]
      #5807125 - 04/18/13 04:57 PM

Weeellll - I don't think I could be convinced of that, to be honest. Too many hibernating/dead projects already, due to lack of funds/energy/time.

I suppose I could ask some of the Danish mirror makers if they want to have a go at it and earn a little money. I know at least one of them is very good and is currently making a 10" or 12" f/4 (or was it f/3?) astrograph.

It is a shame indeed that the mirror is so bad, as the dob structure itself is pretty nice and performs OK and it is easy to track at 250x - 300x, so a better mirror would instantly transform the scope into an awesome observing machine.


Clear skies!
Thomas, Denmark


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Tom and Beth
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Reged: 01/08/07

Loc: Tucson, AZ
Re: There is the telescope "perfect" for the Moon? new [Re: Astrojensen]
      #5807502 - 04/18/13 07:02 PM

It's something to consider. The VERY thin layer of Aluminum is removed in minutes with a polishing lap. I do understand reluctance to add to the mountain of unfinished projects.

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azure1961p
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Re: There is the telescope "perfect" for the Moon? new [Re: Tom and Beth]
      #5807785 - 04/18/13 09:48 PM

I realy considered mirror grinding some months ago. The hundreds of hours involved for the size I wanted and the improbability of success was a total downer. If I were younger with more hours in my day than I have now I'd be compelled. Such as it is tho - I have no such time budget or patience to make a 400 hour flop.

Pete

Edited by azure1961p (04/18/13 09:51 PM)


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Tom and Beth
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Reged: 01/08/07

Loc: Tucson, AZ
Re: There is the telescope "perfect" for the Moon? new [Re: azure1961p]
      #5807989 - 04/19/13 12:19 AM

I'm not sure what size mirror you were considering, but 400 hours?

Like so many other things, it seems daunting until you do it. It does help CONSIDERABLY to have someone guide over the rough spots.


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jonbosley
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Reged: 10/19/05

Loc: Texas
Re: There is the telescope "perfect" for the Moon? new [Re: Tom and Beth]
      #5808593 - 04/19/13 12:41 PM

Well, I believe this is the best current scope for the moon:

web page

Jon


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Astrojensen
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Re: There is the telescope "perfect" for the Moon? [Re: jonbosley]
      #5808929 - 04/19/13 03:20 PM

Quote:

Well, I believe this is the best current scope for the moon:




Wrong! At least in my opinion.

First, it has no aluminum coatings on the primary. That means it has the light grasp of a 6.2" newtonian...

Second, they tout the lack of coatings as an advantage, since it means less scattered light, but hey, isn't the secondary coated? If not, the light grasp is down to that of a 1.4" scope... And if the secondary is coated, the scope has the scatter issue anyway!

Even with my 5" refractor, I run out of light somewhere below 200x, when I want to study the Mare areas and especially the rille regions. Here I often need to keep the exit pupil just under 1mm or preferably larger. My 12" is wonderful for these areas, since it has a luxurious 2mm exit pupil and plenty of light at 150x.

To build a hyper-expensive 28" that is limited to magnifications no higher than those used on a 6", because it has images just as dim, and thus unable to use all the resolution of the large mirror anyway, since most of the details it is capable of resolving can't be magnified enough to be visible, is simply nuts in my opinion. A huge waste of money.

The biggest cause of scattered light in a reflector is not from the aluminum coatings, but from optics with rough or dirty surfaces. I've seen a couple of reflectors with really contrasty, refractor-like images, so I can't believe the coatings are to blame, at least not always. Of course some coatings can be better or worse than others. With freshly cleaned optics, my own 12" newtonian, even with its mediocre optics, produce extremely contrasty views that show myriad subtle contrast features in the lunar Mare. The edge of the Moon snaps from a super bright gray-white to jet black with nothing in between. The crater shadows are ultra black and the bright lunar mountains, even well away from the terminator, show subtle details on their bright peaks. The images look like in my 85mm Zeiss apochromat, just a lot brighter and with much more resolution. Scatter? Not a problem in this scope - when it is clean. If it is not clean, it has plenty of scatter and it doesn't take a lot of dust (or dew!) to scatter a lot of light when observing the Moon.

BTW, I've tested a 6" newtonian with uncoated primary and the image was extremely unimpressive for a 6". It was as dim as that of a 40mm refractor (but extremely sharp at the magnifications typically of a 40mm scope, of course), but it was utterly impossible to use all the resolution of the full aperture, as you ran out of light long before you ran out of resolution.

*

They mention a $40,000 refractor in the ad. For that amount of money, you could get at least a 12" f/15 D&G, if not a 15" f/15, including a huge mount, which would show far more lunar detail than the unaluminized 28" ever can, because of the much brighter images.

And the refractor would of course outperform it even further on targets where light grasp is even more important, such as deep-sky objects.


Clear skies!
Thomas, Denmark

Edited by Astrojensen (04/19/13 03:32 PM)


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jonbosley
professor emeritus


Reged: 10/19/05

Loc: Texas
Re: There is the telescope "perfect" for the Moon? new [Re: Astrojensen]
      #5809114 - 04/19/13 05:13 PM

I don't believe a company of Webster caliber would build and market a scope that does not work and they do market it as a lunar not DSO scope.
I guess if some one ever tries one they could enlighten us. They do offer a full coated version even an enhanced coating if you want.


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Astrojensen
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Re: There is the telescope "perfect" for the Moon? new [Re: jonbosley]
      #5809237 - 04/19/13 06:30 PM

I did say it was in my opinion!

Of course it does work at 200x - 300x (which maximum is what the seeing will support at most places anyway) but at higher powers it will run out of light, especially in the Mare regions. Just like any other 6" scope...

A lot of observers completely fail to understand that the bright images of the Moon in their scopes is a blessing, not a curse, as it allows their eyes to work at maximum speed and catch details between the seeing ripples. The remedy to avoid eye fatigue and making the brain confused from seeing one very bright image and one dark one, is to use a binoviewer. And turn on the outdoor lights, it also helps tremendously, by hindering your eyes from dark adapting. It is better than any filter.

Even at 150x, I strongly prefer my unfiltered 12" over my 5" refractor, since the very bright images allow me to catch subtle details in the Mare and rilles, by maximizing contrast and minimizing floaters.


Clear skies!
Thomas, Denmark


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buddyjesus
Carpal Tunnel
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Reged: 07/07/10

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Re: There is the telescope "perfect" for the Moon? new [Re: Astrojensen]
      #5809798 - 04/19/13 11:10 PM

I prefer a moon that doesn't blind me. It actually at 2mm exit pupil is just on the edge of tolerable. My favorite view is 1.2mm exit pupil(with a #8 yellow filter and 83x) to cut down the glare. I see more when able to have my eye at the eyepiece and I see nothing when I have to take frequent brakes due to eye comfort.

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