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Confused about planetary viewing.


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Hi there,

Im looking to buy a budget scope, like the Celestron 127slt, thats the kind of size and budget i have at the moment.

Re viewing planets through the eyepiece - I have read that Saturn is pin [removed word] on most scopes under 8'' so i take it that it cannot be magnified enough to see a decent view of it, even with more powerful eyepieces?

So my confusion is also seeing beginners guides stating that you can see Saturn and its rings on a good with budget gear - how, if its too small to see?

I looked up two astronomy calculators which show the image possible against what telescope you enter, all the scopes up to 8'' showed Saturn as a pin head.

Also, i see pictures taken via small scopes of Saturn, so i guess they are still pretty tiny but cropped in the editing stage?

As you can see i am somewhat confused....What is possible re smaller scopes and far planets, and how?

Many thanks for any help as i am stymied at present.

Dan.

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Hi Dan

I think the info you have read is wrong!

The scope you are looking at should be more than capable of giving you up to x200 magnification which is enough to give reasonable views of Saturn and Jupiter. The planets don't appear huge in the eyepiece, that is true, but it is plenty to be able to see good detail.

To reassure you, even with my smallest scope, a 76mm refractor, I use up to x160 and am able to see Saturn, with its rings clearly. I can see the gap between the rings and planet, the shadows cast on the rings, some banding on the surface and on good nights, the Cassini division. The 127 should show all this but with better resolution and brightness than in my 76mm.

Don't expect big image sizes, and also plan to spend a decent amount of time observing so your eye gets used to picking out the detail, and you catch the moments of good seeing when the views become pin sharp for a moment or two.

Hope that helps!

Stu

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Hi Stu,

Thank you! I am glad I had this wrong.

So with the SLT127 i would need about an 8mm Plossl or similar to take it to around 187X?

And if i went with an SLT 102, at 660mm FL would need a 4mm eyepiece for 165X. Is that about right?

Cheers!

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Hi Dan

My scope has only 3mm more than yours and Im more than happy with the views of the planets that I can get. When viewing Saturn you can clearly see banding on the planet, defined rings and (seeing permitting) the cassini division. With Jupiter I can make out atleast 5 cloud bands on the planet.

Obviously seeing conditions play a huge part not even from night to night but sometimes from minute to minute. Even if you only get moderate seeing I'm sure you'll get some great views :)

Clear Skies

Matt

Edit - As far as I can see your pretty right with your mag maths. I use a 5mm and 8mm EP's for planetary (conditions allowing of course) which gives 130x and 81x respectively which are great IMO for viewing the planets. Part of the trade off however is the higher you push the mag the more difficult it can be to focus and some people prefer using even less.

Personal preference though :)

Edited by Mattscar
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be aware that some budget scopes are better at planetary viewing than others. generally cheaper reflectors are better than cheaper shorter refractors. longer refractors (perhaps 1m focal length or more) are often very good though.

more aperture = more resolution

a slower focal ratio (e.g. f10) can help sometimes but aperture generally winds on most objects.

I agree with Stu, any of the scopes mentioned will provide nice albeit fairly small views of Saturn and Jupiter. Mars is a lot smaller so more difficult to see detail but certainly possible and the other planets show hardly any detail anyway just either a phase (Venus / Mercury) or a colour (Neptune and Uranus). the moon is pretty good through any scope.

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I wouldn't go to more than about 20th in a 127, and probably no more than 15th in a 102. Highest practical power is found by multiplying the objective diameter by 2 (in mm) but in my experience even that is a little ambitious with budget scopes. That being said the 127 should give you perfectly serviceable views of the ringed planet and Jupiter. Mars for me is a harder target, despite its proximity, but maybe that's just me!

Typed inexpertly from my phone

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Mattscar & Moonshane, good points from you both in additions to Stu's, thanks! :cool:

I am happy now, after feeling deflated before.

Thanks so much for your informative replies, its much appreciated. I shall be sure to ask questions re this if anything else stumps me :grin:

Best

Dan

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Sorry, predictive text. That should read 200x and 150x not 20th and 15th respectively.

Typed inexpertly from my phone

Haha! Yep that did throw me for a loop! right got you, I have that clear in my head - something important learnt today :smiley:

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A couple more things. If planets are your thing then the 127 should be a good choice. It has a longer focal length (1500mm) so will give higher magnifications for a given eyepiece. This does allow you to chose more comfortable eyepieces with more eyerelief, and at f12 it will be quite forgiving.

The mak design also won't show any chromatic abberation, ie colour fringing around the planets which you would get on an achromatic refractor like the SLT 102.

One downside of the mak is a quite narrow field of view so you would struggle to fit in some of the larger open clusters and galaxies but you will be fine with most objects with a longer focal length, wide field ep.

Stu

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Hi DanOrion,

What may be throwing you off a bit, and the issues with some of the eyepiece telescope visual calculators, such as found here

http://www.skyatnightmagazine.com/field-view-calculator

is what you are looking at is small on a computer screen, compared to what it would be like in reality when you press your eye right up against an eyepiece. The image drawn of a planet at such a small size when represented across lets say 200 - 300 pixels across, the detail you can actually resolve in reality given the resolving ability of a typical telescope, including the one you mention, and the resulting sharpness is much better to what you get from looking at that FOV viewer.

Just an aside, but perhaps worth mentioning anyway, you could if you wanted work out roughly for a given screen size how many arc seconds, or fractions of a degree you can actually meaningfully represent in a single pixel for an eyepiece drawn on screen with radius y pixels , and you'll find that the resolving ability is less to what your actual eyepiece/telescope can deliver.

That being said. I tried the viewer above using the 127SLT telescope on that site. If you position yourself such that you see the outline circle of the eyepiece, and imagine what would happen when you press you eye right up against an eyepiece, it actually works quite well. I tried it at 187 times, and for sure it a lot more than just a pin, you cam see the planet, but the clarity in terms of sharpness is just not there as would be the case in reality.

In any case, if that does not make much sense, perhaps I did not explain it too well, too hot today to think and write clearly :D I can assure you that you'll find what you see in the calculator is somewhat underwhelming, compared to what it will actually turn out like when you get your first views.

It is amazing how much can be discerned from a few fractions of a degree in an eyepiece and how much you can see in a telescope :)

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Hi Dan, something else for you to consider, although the design is somewhat dated, the Orthoscopic range of optics, was often the eye piece of choice for observing the planets and is still preferred by many to-day. Baader have recently reintroduced a new Orthoscopic with an increased FOV from their original BGO range, which are still very popular, but no longer made and are now difficult to source s/h, have a look at FLO for details :)

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at 200x - saturn is about the size of a garden pea held at arms length in my scope.

more than big enough to get some terrific detail if the conditions are good.

might not sound a right lot - but consider the light has travelled 850 million miles from the sun to saturn, bounced off its surface and travelled another 820 million miles into your telescope and in to your eye. The idea you can see anything is a bloomin miracle!, especially as Saturn isnt a mirror!

Edited by nicks90
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The 127SLT is a good choice and if well cooled down will give good views of the planets. Lower power, sharper views are better then bigger, fuzzier views so try to aim for around x170 to x220 on magnification, any more and our atmosphere will start to become an issue.

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I think Stu is right. You seem to have been misinformed about the size of objects when viewed with a 127mm scope. I have seen Saturn and Jupiter and even Mars with a 130mm scope (and a 90mm scope) and i cant describe any of them as appearing like pinheads. Yes, Mars was by far the smallest and hardest to see but still had observable features with the 130mm scope.

Its a well known fact that if you buy a "Dob" that you get the best bang for buck and that is why i am suggesting that instead of a 127SLT...........you go for a scope such as a Heritage 130P or even a bigger Dob. You can get more aperture (light gathering ability), for less then the cost of the 127.

This is without doubt the most popular beginner scope. Its an 8" Dob and you would have cash left over for a couple of extra bits that you might want to add.

http://www.firstligh...-dobsonian.html

OK, i know telling people who ask................that buying a Dob is a bit of a cliche round here but there is a good reason for it. It is because they are value for money without compromise on quality.

By all means,if the 127 is the one you are set on................there is nothing wrong with it. I'm just saying for your budget you have choices, be it the 127 (5") SLT OR AN 8" Dob. Its all down to preference (Go-To or manual), and just how portable you want it to be and storage space etc etc.

HTH.

Paul

Edited by LukeSkywatcher
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I have a 6 inch Newtonian and i have had some great views of Jupiter Saturn Mars and Venus, Saturn Ive seen the Cassini division if you can only see a pin there is know way i would be able to see that much detail, Ive seen 4 bands on Jupiter maybe 6 two where very faint but i have seen the great red spot and Ive seen polar ice caps on mars just to give you idea. The 127 mak was the scope i was going to buy before i went for the newt.

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Just to throw in my tuppence!

I've had over a decade of great views of Saturn with an etx90.

Considerably smaller than yours!

It took very good conditions to see the Cassini division, but still spectacular views!

Cheers

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as for storage, if you have the room in your dining room/garage/conservatory to store your scope set up on its tripod - then you have enough room to store a second hand 12" dob in exactly the same space......

now i've gone and done it!

:evil: :evil: :evil:

but if you are unfortunate and have to fully pack away your gear - then the 127 is certainly a good idea in terms of stuffig it under the sofa or in a cupboard

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Paul is right :-)

Forget about Plossl for high magnification. Actualy forget them completely if you are not on a tight budget. Modern eyepieces have decent eye relieve and a wide angle apparent field of view. And 30 to 50€ are still affordable.

Not that the included eyepieces are completely useless, but once you have decent ones, you never want to go back ;-)

I have the heritage 130p, and with a 2.5mm eyepiece (hr planetary, 32€ to 45€) lanets and moon are stunning. Even at 260x it's not too hard to track a planet, especially with a wide angle eyepiece. The one-arm dobsonian mount of the heritage requires you to balance the telescope well and get the friction right at high magnifications, but that's no big deal.

The h130p is very portable, the low focal length has it's downsides (collimation needs to be checked occasionally, outer field of view of cheaper eyepieces is not sharp on f/5) but great for wide field views that a small Maksutov telescope can't provide... And with a barlow or decent 2,5-4mm eyepiece planets and moon are nice too.

More then 200 to 260x does not work most of the times anyway due to seeing/air turbulances.

The h130p costs about 130£/170€. Add a 20mm uwa and 6mm uwa eyepiece, 30€ each, a 16-25€ achromatic barlow, and you have a very neat wide angle eyepiece starter set (32x, 65x, 108x, 217x) that you can complete with a few Hr Planetary eyepieces and a more expensive 25mm wide angle eyepiece later.

More usable stuff are maps/star charts (cartes du ceil freeware, turn left at orion, or other resources, some free online), a red light to keep your eyes adapted to the darkness while reading, and a cheshire-sighttube to collimate your newton/dobson better then with your eye looking through the focuser or a simple collimation cap/film canister that you can build almost for free and work for starters.

IF you have and want to spend more then 130-200£ and you can transport (real dark skies far out of towns/cities show so much more...) a larger telescope (car, bike hanger) a 8" dobsonian will show amazing details on deepsky objects. Even if you plan to get into photography later, it will most likely be a smaller telescope as you will need much more stable mounts then for visual astronomy, and you can use the dobsonian as grab and go telescope visually.

As planets will allways look more fancy on photos, it's hard to describe what they will look like when observing thenm yourself. I do astro sketching occasionally and I tend to draw the planets larger then they where in the view, as perception is different then all the simulations and photos you see online. Keep observing for a while and you will discover more and more without higher magnification. It just takes time, a phase of calm athmosphere, and learning to see.

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