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Planetary telescope

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Hello,

 I am looking for one of those for planetary and lunar observation, as my observational site is plenty of pollution, I dude between a ED100 or a Celestron 6SE or a 8" Dobson..Which is the best for especifically planetary and lunar observations ?

Thanks

regards,

Paulo

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8" Dob! Even though contrast at the same exit pupil will be a touch lower than in an unobstructed scope like the 100ED, the amount of fine detail grows with aperture. I have looked through 4" fracs and my 8" SCT, and the SCT showed more fine detail than the refractors under good seeing,

Ideally, I would like an 8" F/8 newt  to keep central obstruction down.

 

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Specifically for planetary and lunar I'd agree with Michael that an 8" f6 dob would give more resolution most of the time.

That said, don't underestimate the value of a tracking (but not necessarily GOTO) mount when observing the planets and moon at high power, especially if sketching. This might influence your decision as might the possible future solar route. Should this be the case then an ED frac of 100mm or more would be best in my view.

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Bear in mind that the planets will all be miserably low from the UK in the coming 5 years so (1) chose a scope that can easily point towards the horizon and (2) don't expect to be able to use as much magnification as normal which to some extent may negate the advantages of larger aperture. An 8" will do better service on deep sky objects than a 100mm will, but personally, I'd probably go for the 100ED on an equatorial mount if possible. It won't keep up with a dob on deep sky but that  probably won't matter in a heavily light polluted area. it should give you nice crisp views of the moon and planets and double stars and the tracking would be a Godsend for those kind of observations.  :) 

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I think the 8" dob would perform the best all things being equal but the low positioning of the planets over the next few years would push me more towards something that will be able to cut through the atmospherics that we will have to contend with and that would probably be the refractor. Having a tall tripod will help actually getting a planet that is not high in the sky into view. It's not always easy with the low slung dob design.

 

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Aperture wins on planets.. makes them brighter..focal length makes them bigger..so a combination of aperture and high f ratio is what you want..

But as normal funds will dictate

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Aperture always wins. Refractors can have a better image quality then Newtonians - better contrast, tighter stars etc - but the extra detail from a Newt can't be matched. There's a huge difference between 100mm and 200mm!

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Aperture wins if all other things are equal. Bigger lens/mirror brighter image, higher theoretical resolution. But it comes at the cost of bigger telescope and longer cool down. The atmosphere is going to limit resolution to about 1 arc second at a good site with the target at zenith. Planets in the UK typically 40° above the horizon you'll be doing well to get two arc second resolution much of the time. If the big telescope takes an hour to set up and another to cool down, you'll probably only use it three nights a year. If it's quick and easy, you may use it ten times that often. At the university I used to work at we had a 24" cassegrain with a 6" Astro Physics refractor finder. on the vast majority of nights, Jupiter looked better in the finder because the big scope hadn't come to equilibrium and it's not like there's any shortage of light from jupiter. I had much the same experience observing jupiter with the Lick 36" refractor - if I'm brutally honest, the 7" AP set up outside gave a better view. Nothing wrong with big telescopes, they do enable you to do more. But personally I'm a bit wary of the urge to go bigger and bigger as it's not always conducive to increasing your enjoyment of observing :) 

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Generally I agree with the "aperture wins" thing but I was trying to be pragmatic and take account of the reality of where the planets are going to be in the sky over the coming period for observers in the area that I'm in, the UK. My 12" dob has excellent optics that produce very fine planetary images when the targets are well placed and the seeing conditions good. With a planet less well placed and under the common "moderate" viewing conditions, my 120mm refractor often gets very close to the 12" in terms of planetary image quality.

 

Edited by John
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40 minutes ago, John said:

Generally I agree with the "aperture wins" thing but I was trying to be pragmatic and take account of the reality of where the planets are going to be in the sky over the coming period for observers in the area that I'm in, the UK. My 12" dob has excellent optics that produce very fine planetary images when the targets are well placed and the seeing conditions good. With a planet less well placed and under the common "moderate" viewing conditions, my 120mm refractor often gets very close to the 12" in terms of planetary image quality.

 

Got to agree. I sold my C 11 & got a CPC 800 HD. I get better results out of this because I live in a town.

In perfect conditions the C11 was better , but they were few & far between.  Getting a lot more use out of this.

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In 2003 with Mars at its absolute finest throughout the year, week after week my FS128 wiped the floor with countless larger aperture scopes of every major design. Nothing came close to matching the level of intricate detail visible in the 5" fluorite apo. Two scopes did give the Tak a reasonable run, and they were both refractors. An 8.5" achromat, detailed but a touch colourful, and a 4" Vixen fluorite. No Schmidt of any aperture came close, nor did any Newtonian, and there were a vast number of scopes up to 30" on the field week after week, month after month. Hundreds of people visited the astronomy centre - on one evening 300+,  and all who were privileged enough to look through the 128 offered the same opinion, the FS128 beat everything! 

Aperture has its place but on the planet's it is certainly not King! A sharp well defined image is what is needed, so definition is King when it comes to visual lunar and planetary observing, and aperture counts for nothing if the definition suffers. A scope that gives a consistently well defined view is preferable  to one that occasionally might, if all the annoying variables miraculously fall into place, give that one memorable night out of a hundred. In 37 years of visual observing i have only once seen a Schmidt Cassegrain give what i would consider a top class view of Jupiter. I have seen many good views through Newtonians, but on all but one occasion, when a good refractor is alongside the Newtonian, the refractor has given the sharper, better defined view.

Some people may prefer the brighter image of the large apertures but I would choose the scope that delivered consistently well defined planetary views, and especially if it was to be my only scope. For that reason I'd choose a 100mm or 120mm ED over a 200mm reflector or catadioptric for an only scope, knowing that nine times out of ten it will deliver a better result.

Mike

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Light pollution prevents much deep sky observing from my location, so planets and brighter Messier objects are my thing.

I have a 100ED and recently, after a year of gathering side by side observing experience, moved a Skyliner 200 dob on to a better home. The reason? To me, the refractor gives consistently better views of the planets.

I'll go one further. My 100ED gives consistently better views than my 6" achromat too.

Tom

Edited by orley
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i am so happy for you, that 1 night in 37 years you had a memorable night. i must be lucky because most nights that i go out are memorable. maybe you should get a reflector :icon_biggrin:

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16 hours ago, mikeDnight said:

In 37 years of visual observing i have only once seen a Schmidt Cassegrain give what i would consider a top class view of Jupiter.

 

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Its all relative. From my own perspective its about having a tracking mount and a height adjustable chair. Then its about how big a mount I am prepared to live with. This rules some scope sizes out. Then opportunity weather and time can dictate if its worth the effort.

In the end a light weight high quality refractor is carried setup outside in two minutes even if there is only a ten minute window of clear skies either in the evening or the morning before work I get twice as many observation opportunities this way without any fuss.

 

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17 hours ago, mikeDnight said:

In 2003 with Mars at its absolute finest throughout the year, week after week my FS128 wiped the floor with countless larger aperture scopes of every major design. Nothing came close to matching the level of intricate detail visible in the 5" fluorite apo. Two scopes did give the Tak a reasonable run, and they were both refractors. An 8.5" achromat, detailed but a touch colourful, and a 4" Vixen fluorite. No Schmidt of any aperture came close, nor did any Newtonian, and there were a vast number of scopes up to 30" on the field week after week, month after month. Hundreds of people visited the astronomy centre - on one evening 300+,  and all who were privileged enough to look through the 128 offered the same opinion, the FS128 beat everything! 

 

Mike

And I feel privileged that you deemed to share that with us.

 

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On 17/03/2017 at 23:49, John said:

Having a tall tripod will help actually getting a planet that is not high in the sky into view. It's not always easy with the low slung dob design.

 

I would second this. I was looking at the moon recently when very low with the dobsonian and gave up quickly as it was too annoying crouching down. If I had taken my observing chair out I would have been fine but I went out without it.

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One like I've got LOL, but I only got it because the SGL experts dug in and convinced me (I am a novice so listen to what they say as they are experts!).  I've already had some lovely planet views.  The cheaper version is this one https://www.firstlightoptics.com/dobsonians/skywatcher-skyliner-200p-dobsonian.html £285 notes and it's yours! LOL

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Just to add to your conundrum- don't rule out a MAK.  I have the 150 Pro and it's superb on planets, lunar and Globulars.  I've also used it with a 40mm WA EP on more open objects such as M42 and the views are very good indeed.

Edited by recceranger
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On 3/18/2017 at 19:51, mikeDnight said:

 In 37 years of visual observing i have only once seen a Schmidt Cassegrain give what i would consider a top class view of Jupiter. I have seen many good views through Newtonians, but on all but one occasion, when a good refractor is alongside the Newtonian, the refractor has given the sharper, better defined view.

Ho Ho Ho, did you forget to collimate the scope? or let it cool to ambient temperature?, perhaps "should have gone to spec savers" is appropriate...?

I have to wholeheartedly disagree with this comment or you must have been using the wrong SCT "for the last 37 years" :):)

My CPC1100 has given AMAZING views of Jupiter & Saturn. Plus plenty of great detail on Mars. You are welcome to "pop over" as I would not like it to become 40 years of disappointment :)

We all LOVE our scopes (we paid hard earned cash for them) but is it really helping the OP to come out with sweeping statements that clearly can't be accurate or nobody would sell/buy SCTs!

 

Edited by alanjgreen
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I had an 8"f/10 home-made dob once with small secondary and curved spider....it was brilliant on planets and being so slow the collimation wasn't that critical. I've never had astro-friends rich enough to own a FS128 so I'm not qualified to comment on the comparison but I would forward for consideration the OO 6" planetery newt with the best optics option. Compared to the cost of a new FS128 I suspect the bang per buck would be remarkable (if you can mount it well). And with the change out of the FS128 price you could get a slack handful of XW or Deloses....

If you're set on a frac the ED120 is very hard to beat, and commonly available secondhand.

RL

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I'd like to try an ED100 or even an ED80 just to see for my self, but folk more knowledgable than I have suggested I have a suitable scope  as it stands,  and there would not be any significant gain or improvement looking through the refractor? A side by side comparison would be the ideal solution, but I'm set on keeping what I have for much longer now.
 

I don't like EQ for visual use, but If I ventured deeper into astro-photography, it would be an ED80 for my needs after reading a certain book  by Steve Richards! yet most of his subjects are outside our Solar system, and from looking at the published results, its the reason for my choice of an ED80

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