Best planetary 'scopes

[Tomjo59]

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.

[Moonshane]

To some extent a larger secondary mirror (secondary is larger the faster the scope for the same aperture) reduces contrast so slower scopes are better. Sort of. I have a 6" f11 dob and this provides wonderfully sharp views full of contrast. That said the detail does not match my 12" f4 dob. Aperture also matters. I have yet to see views through any refractor up to 4" which come close to either.

[nightfisher]

A 5" scope with a x5 barlow would not be as good as say an 8" with a x3 barlow because at x5 the image would be dimmer than 8" at x3.

A 6" Maksutov is a very good planet scope, as is a 6" newtonian with long focal length f8 or more

[tarotrocola]

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.

[ronin]

For planets there tends to be a degree of detail to get dragged out of the object and for whatever reason refractors appear to deliver greater contrast and sharpness somewhat easier so they are more suited to that aspect.

A large reflector will gave more light for comparitively less cost, so maybe for Neptune+Uranus a reflector is actually better as to an expect they are more like a blue/green star.

I guess a reflector loses sharpness and contrast owing to the "mechanics" of the scope. The edges are not ideal and on a reflector the secondary will double any error. Basically the optics can lead to a little less sharp image.

Hubble is not a parabolic, it is hyperbolic for the reason that a hyperbola is better then a parabola for imaging, but cost more to produce. I suppose that in reflectors that should be the next step - inexpensive hyperbolic mirrors.

You can of course get sharper reflectors but like everything the cost jumps. A slower f number means the edges do not need the high accuracy, so slow reflectors are reasonable on planets.

Finally planets are "bright" they can take magnification so a slow scope - long focal length - again lends it self to this aspect.

On an "ideal" scope either would do but none are ideal.

[nightfisher]

I am a refractor/Maksutov person but, one of the best views of Jupiter was with a 6" OOUK newt, though as a rule my old 180 Mak gave the best planet views, and the 150 mak i now have does a stirling job

[Moonshane]

Aesthetically my best planetary views are with my 16" f4 dob masked to 170mm. The most detailed views occur when I take off the mask and use full aperture in good seeing conditions.

[Caldwell14]

Might I suggest a Mak Newton? No horrible defraction spikes, no CA either and plenty of aperture. You end up with the performance of a very large APO refractor for a fraction of the cost. I still toy with buying one

[John]

Might I suggest a Mak Newton? No horrible defraction spikes, no CA either and plenty of aperture. You end up with the performance of a very large APO refractor for a fraction of the cost. I still toy with buying one

Yes, I was very impressed with the Intes 6" F/5.9 mak-newtonian that I owned a couple of years back. Certainly very refractor-like qualities, no false colour and was also capable of very reasonable wide angle views too. A very versatile scope. If I had an observatory, so cooling was not an issue, I'd be very tempted to own an 8" mak-newt.

[Grotemobile]

I think that the Celestron, CPC series of scopes,

are best for the planets. So easy to set up & use.

[John]

So far I think we have had almost every design of scope recommended for planetary viewing, except (so far) fast achromatic refractors. Perhaps there isn't such a thing as a "planetary scope" these days ?

[Moonshane]

I agree John

perhaps the notion of 'best for planetary' comes from the days when we were less awash with wonderful options at a reasonably accessible price point?

[Dannae]

Great advice and points already. Maximum planetary contrast is a function of the interplay between aperture (which in the case of planets I would argue peaks at 10-12" with regard to diminishing returns versus cost), size and type of secondary obstruction (secondary mirror) or preferably no obstruction at all, focal length, quality of optics and diagonal, number and quality of the telescope's mirrors/lens/correctors in the optical chain, number of elements in and quality of the eyepiece (TMB Monocentrics/Zeiss Abbe ortho's are arguably the best for this), and seeing (also altitude of the target). To this I would add patience, experience, and tracking which gives you more time to process the view (especially if you are using 30 degree Mono's ). I also found that binoviewing can enhance the experience even if 'technically' one eye would be the better option all other things being equal.

Regards

Dannae

[Charic]

Maksutov Newtonian.........I had to check twice? You learn something new  everyday on SgL!

Time to start saving ?

[Qualia]

Aye, I don't think one type of scope can lay claim to being the best for planetary viewing. It makes reasonable sense to assume that each scope type (Newt, Frac, Cassegrain, Maksutov etc) will throw up those that do an outstanding job, those that do okay and those that will be rather lacking.

I imagine a well collimated, relatively smallish central obstruction, longish f/ratio 8"+ and bigger Newt would be an outstanding planetary scope. So too would be an 8"+ and bigger Cassegrain type per se. On the frac front, one would probably get outstanding results with a 6"+ and bigger, f8 and longer Apo or a 6"+ and bigger f12 and longer Achro

Of course, each type will have its own peculiar draw backs and ultimately will be compromised by the given seeing conditions of the evening.

To be honest, whatever system used, however humble the gear may appear, if the night skies are forgiving, something gorgeous and majestic will always reveal itself. I've been out with a little 3" looking at Jupiter and have had just as much pleasure as viewing the giant in the 10".

[nightfisher]

Thinking a little longer about this, i would pin it down to a 180 pro mak, we are talking near APO views with a huge focal length and can be picked up used for about £500.......try getting an APO frac 7" for this kind of money but, the mak is very heavy, and in my own opinion best suited to an obsy set up

[YKSE]

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.

I think your question is anything else than daft

As already mentioned by others, For the same aperture, a well-corrected refractor (a long achro or good APO) will be outperform any other type of scopes, simply because there's no Central Obstruction(CO), as described here:

http://legault.perso.sfr.fr/obstruction.html

talking about newtonians with different focal ratios, to get the same illumination of field of view, the shorter focal ratio newt has to have bigger secondary mirror, therefore bigger CO than the ones with longer focal ratio, thus somewhat lower resolution.

About the barlows, if we consider a 2x barlow in a f10 newt, and a 5x barlow in a f4 newt(same aperture), the scopes work like a f20, using the same eyepiece get very different exit pupils, not directly comparable results. If using different eyepieces to get the same exit pupil, the small CO in f10 newt will be the better one.

This is of course assuming everything else equal, including the observer.

[Stu]

In theory I have two lovely planetary scopes. I say in theory only because I've yet to have decent views due to either weather or planetary position.

The scopes?

Vixen 150ED F9 refractor. Lovely crisp and contrasty views.

12" Orion Optics f6, 1/10th wave with a 50mm secondary ie sub 3% by area.

As a brief summary I would say that the refractor gives more pleasing views to my eyes, but the 12" clearly has more resolution and shows more detail.

I agree with the previous comments though, any decent scope with good contrast and resolution has the potential to show lovely planetary images. I can vouch for the fact that Shane's 170mm Dobfractor (ie the 16" masked to 170mm) gives stunning planetary views.

Cheers,

Stu

Sent from my iPhone using Tapatalk

[Tomjo59]

Many thanks for all the responses everyone. Lots of factors to take into consideration, obviously, and that is just for a planetary scope ! It also emphasises that there is no one instrument that suits all purposes.

[Alkaid]

I think it depends on the observing location as much as the telescope design. Last April I had unbelievable views of Jupiter from a very cold Yorks Dale, seeing and steadiness were A1. Using a humble 90mm achromat, I counted 7 bands on Jupiter. Turning to Mars, which was low, the main features such as Syrtis Major and the polar caps could clearly be seen.

I was just gutted that I did not take the larger Newtonian.

Its now my belief that even if you have a so called Planet Killer, you may only realise its potential just a few times under UK skies.

God, that's pessimistic isn't it!

[F15Rules]

I'm happy using this one . 5" F15 D&G refractor (the bigger one!)

Just had the tube rebuilt by Moonraker Scopes: new baffles, ray traced, full Protostar flocking to increase contrast, drilled for new 60mm finderscope, moonlite focuser fitted and tube shortened by 130mm for binoviewing. Can't wait for Jupiter!

Pic shown doesn't include mods, will post up first light soon..

Dave

[jetstream]

Great set up Dave, what tripods are you using? I'm in the market for one to be used with the 120ED

[F15Rules]

Great set up Dave, what tripods are you using? I'm in the market for one to be used with the 120ED

Hi Gerry,

I have the scope mounted on an upgraded CG-5. For visual it's ok, but could really do with an EQ6 mount. I do have ADM saddle and puck upgrades on the CG5 which assist stability. It's not the weight of the scope (around 28 pounds all in with finder, moonlite focuser etc), but the length of the tube..

The tripod is a home made (not by me) heavy duty hardwood unit which is fixed height and very stable indeed. I think it's actually the main reason that I can get away with using the CG5 head, it's so good at absorbing vibrations.

Hope that helps,

regards,

Dave

[jetstream]

Thanks Dave, yes it does help and I'm leaning toward a setup similar to yours, Binos too.

Clear Skies

Gerry

[cotterless45]

Don't think anyone has mentioned the SW 150pl on eq3-2. I filled the legs with mortar mix and put a polarscope and an ra motor on. It's rock steady.It gives wonderful sharp contrasty views of planets. Closing down to 120mm gives a comfortable f10. a really lovely bit of kit.

Nick.