Best planetary 'scopes

[swamp thing]

I rarely observe planets myself. I have however often observed in a group where someone is. Ive found that the best Planetary views are almost invariably given by the largest scope. 

I observe with other astronomers nearly every time I observe so i've been lucky to observe through a vast amount of scopes in various conditions and have found that often these so called planetary scopes very rarely out perform regular all-rounders. ED or apo glass and maksutov optical systems often fair no better than skyliners. Seeing pulls no punches and effects all exactly the same. In fact my homemade 10" dob with so-so optics often kicks the butt of far more expensive glass. 

There simply is NO substitute for aperture. If the seeing is good the biggest scope will always win a resolution battle. 

[Tomjo59]

I rarely observe planets myself. I have however often observed in a group where someone is. Ive found that the best Planetary views are almost invariably given by the largest scope. 

I observe with other astronomers nearly every time I observe so i've been lucky to observe through a vast amount of scopes in various conditions and have found that often these so called planetary scopes very rarely out perform regular all-rounders. ED or apo glass and maksutov optical systems often fair no better than skyliners. Seeing pulls no punches and effects all exactly the same. In fact my homemade 10" dob with so-so optics often kicks the butt of far more expensive glass. 

There simply is NO substitute for aperture. If the seeing is good the biggest scope will always win a resolution battle. 

Hmm. more food for thought. Steve's post sort of goes back to my original question, can supposed 'planet killer' scopes with long focal lengths (whether newts, cats or 'fracs), produce significantly better views of planets or the moon than short FL 'light buckets', given that the latter would require, say a 5x Barlow to give sufficient magnification and image scale?

I was strongly considering buying a Skywatcher Skyliner 300P FlexTube GOTO, but as my main interest is planetary and lunar observation, am a bit unsure. The extra aperture would surely allow greater detail to be resolved, although of course the objects are bright enough not to require the extra light-gathering capability.

[John]

It's a very interesting topic and one I've seen discussed many times over the years, mostly without a real conclusion, it has to be said.

I observe solar system targets more than DSO's on the whole and find my 12" F/5.3 dobsonain does a pretty good job of resolving planetary details. That said, I'm often surprised just how close my ED120 refractor can get to the planetary details that the much larger scope is delivering when I've compared the two side by side. Turn to DSO's and the dob runs away with it of course.

I've had a few nights when the seeing conditions have been really top class, not just good but truly superb. On those nights and during the stabler moments on other occasions the larger aperture has shown what it can really do and it's quite eye opening

Pity we don't get such conditions very often

[cotterless45]

Depends what else you'd like to see. Don't forget that there aren't always planets up. In the great scheme of observing they can be pretty small fry until opposition comes.

Here are two roughs of Mars , with a 150pl and a Vixen 102 achro. Both were fortunately observed on a clear night of good seeing and transparency.

Nick.

[F15Rules]

I don't think anyone could dispute that, all things (conditions) being equal and ideal, the larger aperture has to beat the smaller. And if we lived in the Arizona desert those occasions might be quite common. Sadly, here in Blighty we get ideal conditions (or anything approaching ideal) all to rarely. That being the case, it does seem that smaller apertures of perhaps up to 7 or 8 inches sometimes (and more often up to 6 inches), of all types of scope seem to give of their best more often..

I think Cotterless' drawings illustrate the point: both scopes, 4" quality achromat and 6" quality newt, delivering similar quality images with good detail.

Dave

[nightfisher]

It may also be a factor as to what style of telescope the observer is "drawn to" as to what scope that person would suggest as best planet scope, when it comes to detailed planet observing, i admit to having a liking for Maks, so it fair to say i will recommend a Mak, another person that is say, drawn to refractors is going to say fracs, and so on.

I do feel a good Mak is still going to be a very strong performer on planes and Luna, simple fact of the focal length giving more image scale, however an 8" newt with a native focal length of about 2000mm is going to beat a 7" Mak, but on the other hand a 2 mtr newt is not very usable 

[nicks90]

I would agree and disagree.

The best planetary scope has to be a 12" f5 DOB.

Just think about it, you get no CA in a reflector, astigmatism/coma and any other abherations only occur towards the edges and that just means you keep the planet centred.

In times of poor atmospheric quality, stop it down to 120mm f12 for great contrasty views even in rubbish skies. Stopped down it will probably rival an expensive frac! Then, under good conditions open her up to the full 12" and get blown away by sheer detail and resolution!

Add a x2 barlownand you have 3 metres of focal length. More than enough to get your kicks with.

Plus when no planets are about, its a killer DSO light bucket. What's not to like?

[scarp15]

I was strongly considering buying a Skywatcher Skyliner 300P FlexTube GOTO, but as my main interest is planetary and lunar observation, am a bit unsure. The extra aperture would surely allow greater detail to be resolved, although of course the objects are bright enough not to require the extra light-gathering capability.

Dont be put off from buying the skywatcher 12" flextube, as it will perform brilliantly on planetary and lunar observing - that was my own impression when I used to own one. Also as nicks90 has mentioned, you can step down the aperture and increase the focal ratio by making an aperture mask to suit the seeing conditions. I have been encouraged to do just this, with advice from Moonshane, for using my 14". Just received a compass cutter and got hold of some card so will make this at the weekend.

I think though as Nick and others have mentioned,  that there is a lot to be said in favour for a 6" F8 newt to and I am quite attracted to the practicality's and am contemplating an OOUK VX6 F8 for a portable and effective grab and go set up.   

[YKSE]

If we talk about different apertures, different astronomers and different sky conditions, we're talking about three major factors which have bigger impact than central obstructions. An experienced astronomer will surely see more details than the inexperienced one in the same scope. The ssame observer will see much more detail in 8" under tranparent sky with good seeing than 12" with bad seeing, etc.

As we're not blessed with tranparent good seeing that often, my wild guess is that scopes USED MORE OFTEN are most likely the best planetary scopes.

[scarp15]

Quite right, it can be the consistency to which you are able or committed to spend time outdoors night after night with the scope you have, in undoubtedly varying seeing conditions and to study the same subject intently. My first telescope was an 8" Celestron SCT Celestar, the views I received of the planets improved as I gradually improved the quality of my eyepieces to eventually include Televue Plossls. The scope provided crisp images with periods revealing tremendous detail and always seemed to provide a quite intimate view. I don't think that I have devoted committed time to planetary observing in the same way since I sold this scope.  

[bond19]

Not massively qualified to comment (telescope wise). But I'll approach from another angle. Quality of the optics have always been a factor for me. The views through a pair of Swarovski binnacles is truly excellent compared to lesser optical counterparts. With DSLR's always spend the money on quality glass, not the body. And with telescopes I maintain this approach. I have owned a 10" dob, Meade ETX 125 and Nexstar 8se. All very capable scopes. Currently I only own a Tele Vue 102 with a range of TV Ep's. I know it can't compete on aperture, but the razor sharp and highly detailed planetary and moon views are the best I've ever seen. Plus I can make out stark nebulosity in Orion, and nebulosity across M45, and enjoy sharp views of open clusters. This for me is quite astonishing considering the meagre 4 inches of aperture. But the quality of the optics are undoubtedly helping my viewing experiences punch well above their weight. Plus I can grab it and literally be viewing in less than 2mins from leaving my sofa. This has resulted in much more frequent trips under the stars, which I would otherwise have chosen to ignore. 

[Tomjo59]

Dont be put off from buying the skywatcher 12" flextube, as it will perform brilliantly on planetary and lunar observing - that was my own impression when I used to own one. Also as nicks90 has mentioned, you can step down the aperture and increase the focal ratio by making an aperture mask to suit the seeing conditions. I have been encouraged to do just this, with advice from Moonshane, for using my 14". Just received a compass cutter and got hold of some card so will make this at the weekend.

I think though as Nick and others have mentioned,  that there is a lot to be said in favour for a 6" F8 newt to and I am quite attracted to the practicality's and am contemplating an OOUK VX6 F8 for a portable and effective grab and go set up.   

Thanks Iain, that's an excellent point. With a nice big 12" mirror, there is the scope to stop it down to increase the focal ratio. The other attractions of the Skywatcher were the fast set-up time, and the fact that it is driven. Others on here have commented on the accuracy of the tracking - saves that constant 'nudging' when trying to concentrate on a particular feature.

[timwetherell]

I think it depends on the observing location as much as the telescope design. 

I agree! The seeing is massively important and you only know what the seeing is like if you're out observing. And you're only out observing a lot  if your scope is easy and convenient to set up. So the old adage "The best scope is the one you use" is bang on here! When I had an 8" apo and a 5", I used the 5 much more often because it was just so much easier to set up. 

Having said that, if one could be bothered setting the monster up, and if the atmosphere was in a good mood, it was a cracker of a planetary scope But the difference between the 8" and the 5" was 1000x less than the difference between a night of good seeing and one where the atmosphere was turbulent.

[lensman57]

Sorry if this sounds like a daft question, or one that's been asked already, it may be that I am missing something.

When reading recommendations for types of telescope for different types of observing, one often reads that the 'ideal' telescope for planetary and lunar viewing is a long focal-length refractor or Newtonian reflector, but is there any reason why, let's say, an f5 newt with a 5x Barlow lens would not be just as suitable as an f8 newt with a 3x Barlow?

I am assuming here that the telescope would be on a driven mount, so that manual movement at high magnifications would not be required.

The best planetary scope is the one that a) you can afford b ) you can carry c) you can make use of in other fields of astronomy as the planets not always accessible. Having said all that a large aperture SCT on a suitable mount is quite flexible. The best " affordable"  ones are the Maksutov designs and the best of all these are the INTES Rumak_Maksutov scopes but these are rare and pricy. I quite like my SW 100ED DS PRO F9 for having a look at the Moon, Mars or Jupiter. Hope this helps.

Regards,

A.G

[denis0007dl]

My Mak90 produces good planetary views, of course my 12" dob is better, but considering aperture and the size, the Mak90 is a lot more efficient for this task.

I agree with you!

[denis0007dl]

.......I can vouch for the fact that Shane's 170mm Dobfractor (ie the 16" masked to 170mm) gives stunning planetary views.

Cheers,

Stu

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Now that would be interesting to look through!

[Peter Drew]

As soon as I get a decent clear night I will be trialling a 4 aperture mask on my refurbished 30". The mask offers 12" F10, 10" F12, 8" F15 and 6" F20. Should cover most seeing conditions. 

[Stu]

Now that would be interesting to look through!

It was!! :-)

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[Stu]

As soon as I get a decent clear night I will be trialling a 4 aperture mask on my refurbished 30". The mask offers 12" F10, 10" F12, 8" F15 and 6" F20. Should cover most seeing conditions.

Hi Peter,

Out of interest, what happens if you use four equal apertures positioned between the secondary vanes?

I know that this could be described as just a very thick spider, but if made from very blackened material would it avoid the normal scatter and diffraction from the spider?

I'm sure the answer is negative because there's no such thing as a free lunch, but am interested none the less

Stu

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[Peter Drew]

Hello Stu. The short answer is I don't know, I'll report back as soon as I can try it. As for free lunches, an off axis mask producing a reduced aperture of longer effective focal ratio is still not quite as good as the same conventional aperture and native focal ratio. This is because the off axis portion is not a true figure of revolution. If you imagine a normal mirror looking like a lp record with the grooves representing the figure, if you cut a disc from between the centre and edge the grooves will no longer be concentric. The difference is very small but as you know the parabola varies in its curve from centre to edge. Another interesting effect from using an off axis mask for a reasonably long session is that when you remove it and perform a knife edge test to the mirror the exposed circular area shows up clearly due to the temperature differential.      

[nicks90]

I have heard of a double aperture mask, the benefit being the image is in perfect focus when the 2 images perfectly overlap into one at the eyepiece.

[Peter Drew]

Yes, this was one of the first mask focusing aids, now apparently improved upon by the Bahtinov mask. 

[timwetherell]

As soon as I get a decent clear night I will be trialling a 4 aperture mask on my refurbished 30". The mask offers 12" F10, 10" F12, 8" F15 and 6" F20. Should cover most seeing conditions. 

9" mask on my friends 24" Dob gives cracking planetary views, much like a 9" apo so good hunting