I hope to observe planets like Jupiter and Saturn, and moons. I am a novice when it comes to telescopes and I know images in magazines are not taken with at least 12-inch telescope in a middle of nowhere. Is it possible to view Saturn in little yellowish and Mars in little reddish using following telescopes? I am going to buy one of them. Which one is worth more for the money with the price difference?

I am living in Sri Lanka (a country close to the equator) in a suburban city.

Option 1 EQ-Reflecting telescope

Option 2 EQ-Reflecting telescope

  • 1
    Just for the knowledge of it. You could check also this site (its my favorite site) robtics.nl – Julian Sep 15 '14 at 8:51
  • I think you should go with bigger focal length since planets and moon are relatively bright and you need good resolution for details – Pavle Gartner Sep 30 '14 at 17:00
up vote 4 down vote accepted

Go with Option 1 (135mm) as it has bigger light collecting area, i.e. diameter of primary mirror. It will enable you to see faint objects and it will also help you to see the dim objects under a greater zoom eyepiece, e.g. 4mm or 10mm.

Also, don't fool yourself with the bigger numbers advertized by telescope vendors like 238X zoom or 300X zoom.

First, these are zooming power using Barlow lenses also the more you zoom in on any object, the less light you gather on the mirror and hence objects will look much fainter in appearance. I will suggest the 10mm eyepiece with a 135mm telescope (Option 1) will be sufficient for you to observe planets like Jupiter, its Galilean satellites, Saturn's rings and also many Messier objects like Andromeda Galaxy M31, the Honey Bee Cluster, and open star clusters in the Auriga constellation.

Also bear in mind that you live in a country area closer to sea like here in India and the weather will be hot and humid. So ask the vendor about special coating which protects the mirror from rusting (spots on mirror due to moisture) during the humid monsoon season as at least for 4 months it will be humid.

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    Looks like both scopes use the same mount, which appears a bit on the skimpy side. The shorter tube of the f/6 will give you less jiggle. – Wayfaring Stranger Sep 15 '14 at 19:14

Is it possible to view Saturn in little yellowish and Mars in little reddish using following telescopes?

It is definitely possible to observe the rings of Saturn with telescopes this size. Even the Cassini division should sometimes appear visible, if the instruments are well collimated and seeing is not too bad. In terms of color, Saturn is just a boring buttery-yellow even in bigger scopes, so I wouldn't worry about that.

But Saturn is getting lower in the sky these days. If you hurry up and get the scope quickly, you may catch it for a few weeks at sunset, low in the western sky. After this, you'll have to wait until next year.

Mars is a different animal. Most of the time, all you'll see is a bright brick-red round dot, even in a bigger scope than these ones. But every couple years Mars is at opposition, when it's closest to Earth. We just had one a few months ago. Then you can see some of the big features, such as Syrtis Major, or the polar ice caps, or Hellas Basin full of frost or fog, like a big, bright white area.

However, that's only doable briefly around oppositions. The scope must be in perfect collimation, and seeing must cooperate.

http://en.wikipedia.org/wiki/Astronomical_seeing

If everything is at maximum parameters, I'm sure you could see Syrtis Major in a scope this size. During the last opposition, I've seen all of the above features, plus more (Utopia Planitia, Sinus Sabaeus, etc), in as low as 150 mm of aperture, in a scope with great optics, perfectly collimated, during nights with excellent seeing.

Anyway, for Mars you'll have to wait until the next opposition, in May 2016.

Later this year, in December, Jupiter will start rising in the East, and you could use your scope to watch it - an aperture like this is enough to see the 4 big moons and at least 2 equatorial belts. It will be high in the sky at a comfortable time in the evening early next year.

Until then, you can always observe the Moon, two weeks out of every four.

Also, the planets and the Moon are not the only things accessible with this aperture. Most of the Messier objects are visible in a 100 ... 150 mm scope, even in suburban areas. M13 is spectacular at any aperture above 100 mm. The Great Orion Nebula is awesome even with binoculars. The Pleiades are great too. Most of these deep space objects require low magnification for the best view, but every case is a bit different.

Plenty of double stars out there, too: Mizar, Albireo, even Polaris. All visible in small apertures.

I am going to buy one of them. Which one is worth more for the money with the price difference?

The instruments are about the same. In theory, the bigger one has a bit more resolving power and a bit larger collecting area, so theoretically it should be slightly better.

In practice, with mass-produced instruments like these, it usually depends on the build quality, which can vary.

The smaller instrument is an f/8. The longer focal ratio means less aberrations; it also makes it easier for cheap eyepieces to function well, whereas at f/6 ... f/5 a cheap eyepiece may start to exhibit aberrations of its own (independent of telescope aberrations).

Also, an f/8 is easier to collimate than an f/6.

Overall, I would look at it as a matter of price. If you can easily afford the bigger one, get it. Otherwise, the smaller instrument might be a bit easier to maintain, is less demanding in terms of optics, and it should perform pretty close to the other one - all else being equal.

But since you're focused on planetary observations, remember this:

It is far more important to learn to correctly collimate your telescope, and develop it into a routine whereby you do a quick collimation check every time before you observe - it only takes a couple minutes. For planetary observations, the smaller telescope, in perfect collimation, will perform far better than the larger one, uncollimated. Heck, the little scope, perfectly collimated, will perform better on planets than a MUCH larger telescope, uncollimated - that's how important collimation is.

Improper collimation, or lack thereof, is one of the major factors for lackluster performance for a majority of amateur telescopes (along with poor quality optics - but there's nothing you can do about that, whereas collimation can be improved).

Search this forum, or just google, the term collimation, and read the numerous documents you'll find. Or start here:

http://www.cloudynights.com/documents/primer.pdf

Or here:

How can I collimate a dobsonian telescope with a laser collimator?

The owner's manual should also provide some recommendations regarding collimation (I hope).

  • Seller told me, see without eye piece. If you can see your eye on very centered in the mirror then all OK. Is it true? – Kasun Sep 17 '14 at 17:12
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    It's a good start, it's something you should definitely do. But it's not enough to bring the instrument up to 100% performance. – Florin Andrei Sep 17 '14 at 21:45

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