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tico

Planetary telescope

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On ‎17‎/‎03‎/‎2017 at 15:21, tico said:

 

 between a ED100 or a Celestron 6SE or a 8" Dobson..Which is the best for especifically planetary and lunar observations ?

Thanks

regards,

Paulo

Each of these will reward you with good planetary and lunar observing and each as explained in the above posts will have their attributes. Perhaps it also depends on where you are located in terms of observing and the time you may plan on sessions. If in the UK, then all manner of weather comes and goes and often a rapid reaction approach is needed perhaps accepting short periods. In this scenario perhaps the ED100 is best. In good seeing and when critically collimated, the 8" dobsonian is superb and is versatile for resolving globular clusters and depending on your extent of light pollution (or preferably if you can get to a dark sky), galaxies. the 6SE will of course have the convenience of tracking capability. Also depends on what eyepieces you plan on using, with my 8" F6 dobsonian, for manual tracking ease I prefer ultra wide or wide for planetary and lunar, I am less fussy with my 76mm frac which is also my favourite 'rapid reaction' scope and I love the wide field for lunar. 

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7 hours ago, alanjgreen said:

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!

 

I stand by every word of it Alan! The whole period of scopes alongside eachother over almost a year of planetary observing, when all the brighter planets were high and well placed for observation, is one I'll never forget. The scopes were all collimated and in very good condition. As the planet's were so high in 2003 they were rarely affected by excessive turbulence, and as all the scopes were perminantly at thermal equilibrium, they all had the same level playing field. Yet it was the top end refractors that won the day by delivering consistently high definition views that were sharper than anything else there. What they lack in theoretical resolution, they make up for with their amazing ability to force most of their light, and therefore the detail, into producing the tightest Airy discs and detailed visual images. They deliver images with the least noise possible! In contrast the SCT, while a great imaging instrument,  is incapable by its very nature, of creating an image that is as sharp as that of a refractor. The SCT may very well at times give pleasing, even detailed views, but it delivers soft views by comparison. A Maksutov is a much better instrument choice for visual planetary. 

Looking at it from a different perspective, I would never consider the average refractor a deep sky instrument, though they give pleasing deep sky and rich field views. I've used SCT's for deep sky observing and they are excellent, particularly on galaxies and globulars. However, their field of view is limited, so by their very nature they can't compete with the large aperture Newtonian which is King when it comes to going truly deep; nor can they compete for rich field views with a short focus frac. It's horses for courses. Refractors are excellent visual planetary scopes that are the least affected by poor seeing. They are generally highly portable and tough, and only under exceptional circumstances need collimating. Fracs are expensive though, at least the top end ones are, yet they remain insanely popular despite their small aperture and relative high price tag.

Mike

 

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Don't forget that some Dobs will track (& goto) if you put your hand deep enough into your pocket.  Certainly enough to track planets for long enough to sketch them.  I am also a big fan of my £13 water butt stand for giving my 8" Dob a bit of height!

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2 hours ago, JOC said:

Don't forget that some Dobs will track (& goto) if you put your hand deep enough into your pocket.

An EQ Platform is a great way to get tracking capability on a manual dob to help when sketching etc.

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"This is an amazing telescope. It takes high magnification like nothing else I’ve used and has provided the sharpest, most detailed lunar and planetary views of any scope I’ve owned. It really is “refractor like” and completely outclassed my Takahashi FS128 (itself a superb instrument) and in many ways equals my more recent 7 inch TMB APO. "

http://scopeviews.co.uk/OrionOptics200Dob.htm

One of many articles about newts with good optics and optimized central obstructions....  and many SCT's give excellent performance as well. My own 10",15" dobs "completely outclass" my SW120ED giving equal sharpness with much more detail.

 

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Well I've used 3 instruments tonight:

- 11x70 binoculars to view Mercury and the very slim cescent of Venus

- Tak 100 to view Jupiter

- 12" Orion Optics dobsonian to view Comet 41P Tuttle-Giacobini-Kresak, M51, M81, M82, NGC 3077, M108 and M97.

All three instruments were a pleasure to use. All were the right tool for the job on the targets listed and I'm very pleased to own all of them :grin:

Between them, they turned a decent night into a memorable one.

Edited by John
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4 hours ago, jetstream said:

"This is an amazing telescope. It takes high magnification like nothing else I’ve used and has provided the sharpest, most detailed lunar and planetary views of any scope I’ve owned. It really is “refractor like” and completely outclassed my Takahashi FS128 (itself a superb instrument) and in many ways equals my more recent 7 inch TMB APO. "

 

http://scopeviews.co.uk/OrionOptics200Dob.htm

One of many articles about newts with good optics and optimized central obstructions....  and many SCT's give excellent performance as well. My own 10",15" dobs "completely outclass" my SW120ED giving equal sharpness with much more detail.

 

 

In fairness, the author of the linked article repeatedly points out that those exceptional views occured in rare, fleeting moments of (almost) perfect seeing. The key words here are 'rare' and 'fleeting', which probably is a good summation of seeing in the UK, and rather demonstrative of average conditions.

Everything is subjective, of course. That's part of what makes life fun!

Tom

 

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I have a 120 ED frac, and 150mm f11, 12" f4 and a 16" f4 newts. All give good to excellent views of planets depending on the conditions at the time. To my mind, and with my scopes at full aperture, there's no doubt that as you go up in aperture, the detail visible on planets increases. That said, other than in exception steady seeing (I have rarely encountered this - maybe three or four times ever), the percentage of time that the image remains as sharp as it can be is smaller as you go up in aperture. If you are the sort of person who can accumulate this data with your eyes/brain and 'merge the images' then a large aperture is a good thing. If you prefer a smaller, dimmer, sharper image possibly with less contrast then a smaller aperture might be good.

I like having several options and if I have a big scope out and the seeing is not great, I use an aperture mask which creates a obstruction free 170mm f11 scope in the case of the 16" f4 and 110mm f12 in the case of the 12" f4 (both with paracorr). With the former, I have had my best views of e.g. Mars although I have not been observing as long as many in this thread.

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A lot of it is down to observer skill. With large aperture SCTs which have lower contrast not only do you have to train your eyes to see more subtle detail but you have to have patience for those fleeting moments when the conditions allow fine detail to be seen. If you are out for a quick view then a smaller aperture may well do. If you want those really fine, delicate details, then patience and attention are a must - as is a large aperture.

It goes without saying the collimation on an SCT is critical. Even a slight imbalance can destroy the image quality. To say an SCT never needs collimating is misguided and leads a lot of people to conclude their scope isn't capable.

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Yes the collimation of SCT's is critical and I wonder if many of these scopes are slightly miscollimated diminishing the views. A friends C8 provides vg views but is perfectly collimated.

As far as seeing goes- I lower the mag in my 15" down to where the 120ED usually runs under poor seeing and I find no need to set the frac up... One more thing- binoviewers- I find that low mag binoviewing provides a "larger" image than mono at the same mag while retaining more detail inherent to larger aperture.

And by low mag I'm talking 175x-200x on Jupiter...

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Must admit I admire OP Paulo for get People going :rolleyes:.

Think he`s gone

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