What size/power 'scope would show detail on Jupiter/Saturn?

[Kane]

Here's the usual conundrum, I'd like a scope with the grunt to resolve reasonable detail on targets such as Jupiter/Saturn BUT at the low end of the price range - I was inspired to take up a bit of casual star gazing by the Heritage 76, nice and cheap and also convenient to store and setup. I went to YouTube to search for reviews and on the Scopes N' Skies channel I found a good review but also a review of it's bigger brother the Heritage 130P FlexTube which was also priced well but then the EXPLORER-130EM 130mm catches my eye at only £30 more - now I'm into a scope that is less convenient but potentially suitable for astrophotography because of the motorised mount AUGH

While not being completely out in the wilderness the skies are much darker here than my native Geordieland so there is potential for going out past solar system objects.

Of these three, given the sort of targets I'm interested in which would do a better job?

1) Heritage 76 (3") Mini Dobsonian Telescope (no f/ rating in the advert that I can see)

2) Heritage 130P FlexTube™ 130mm (5.1") f/650 Parabolic Dobsonian Telescope

3) EXPLORER-130EM 130mm (5.1") f/900 Newtonian Reflector with RA motor drive

Appreciate any advice you can give folks

[Capricorn]

Going to upset the reflector people but for detail a refractor gives a sharpr image.

I have seen more detail on Jupiter at 60x with a refractor then at 140x through a reflector. Viewing was one day apart under what appeared to be similar/identical conditions.

Looked at Jupiter 4 weeks back through an 8" dob and while good the sharpness was absent again.

Would suggest that whatever you get you think carefully about an f/5 scope. For 130mm dia mirrors they are unnecessary an f/7 or f/8 would be a lot easier to live with and use. Wish they did a 130PL as they do at the 150 range of scopes. Could/would you stretch to a 150PL ? (£245 150PL+EQ3-2)

[Astro_Baby]

I'd go along with a refractor for better planetary work BUT it depends on your budget. From the three you have listed I would go with the 130EM/900. It will be good on planets and has a tracking motor which will make life easier at high magnifications. It will also be good on deepksy and wont be so tough on eyepieces.

[tinvek]

+1 about refractors, i've got a 250 skwatcher dobs and a c80 ed refracto rand despite its smallerdiameter and having half the focal length, the c80ed gives better views of planets anyday ( er any night )

[Astro_Baby]

Bear in mind of course thet Jupiter and Saturn show very little detail relatively- with Jupiter about the best you will get is the the 4 Galilean moons and being able to see the two main cloud belts (southern equatorial belt and northern equatorial belt) and the red spot (which is actually like a grey smudge). You shoud be abe to spot shadow transits of the moons under good conditions.

With Saturn you will be able to see the rings and the largest moon (Titan) easily enough. When the rings open up a bit (they are nearly dide on at the moment) you will be able to see the gap betwene the rings and the planet and, under good conditions which permit higher magnification, the Cassini division which is a large gap between the rings.

To bring out detail you may need some filters - some people like them and find they help, others find them pointless. I quite like a light yellow and a yello/green filter both of which help to bring up the contrast a bit on Jupiter without darkening the image too much.

ALl of that should be visible in a 5" reflector but bear in mind it wont be a view like hubble gets or like you might see in images of the planets.

[Kane]

That's great folks - thanks

[sixela]

Going to upset the reflector people

"Reflector people" also look through refractors, you know --and appreciate what they're good at. i'm not upset by people liking refractors, and I'm not really upset even if they make untenable arguments about their superiority; I just don't let the arguments stand unopposed.

There are enough advantages in each of the different designs not to have to invent imaginary ones or to exaggerate. Unless, of course, you're desperate to claim one design is superior to all the others all of the time.

but for detail a refractor gives a sharpr[sic] image.

If it's as large. If it's not, then the devil's in the details. The problem is that there are enough nights of good seeing to make a 250mm or 300mm scope worthwhile (at least here) for looking at planets, and let's say that getting a 12" Dob on a platform is slightly more practical and economical than getting that 300mm APO or 300mm f/36 achro .

I have seen more detail on Jupiter at 60x with a refractor then at 140x through a reflector.

That can have many causes. The reflector may be:

-smaller

-out of collimation

-not cooled down yet

-have pinched optics

Frankly, even my Starblast (which needs very good collimation) delivers images of Jupiter at 140x that *no* scope can deliver at 60x. Not even a TV101. Refractors may be good and even better at equal aperture than anything else (provided the chromatic aberration is held in check one way or another), they don't trump the laws of physics or make your own visual acuity better (60x is not a lot of magnification when looking at planets, and on many scopes at that magnification your own visual acuity is what limits the visibilty of details unless the seeing is exceptionally poor).

Now, the images in a large reflector aren't going to be as aesthetically pleasing. But one of the reasons is that to resolve small details, you will have to resolve the seeing, so you'll end up with a less stable image, which only reveals its best details in brief moments of better seeing.

Yes, I *do* know people who prefer the view through their 80mm refractor to the view in my 400mm reflector at 600x. Even though they'd probably be hard pressed to see Io hovering over Jupiter as a disk with detail in it (two dark spots at the poles and a yellow middle).

Viewing was one day apart under what appeared to be similar/identical conditions.

Well, if a reflector can't give you sharp images at 140x and it has more than 114mm aperture, the seeing isn't very good or you aren't managing the reflector properly.

Which is a distinct possibility. Reflectors are more fickle beasts than refractors (once they're baffled and collimated properly, but of course once they are you never need to do a thing anymore, and usually they come well collimated from the factory.)

Would suggest that whatever you get you think carefully about an f/5 scope. For 130mm dia mirrors they are unnecessary an f/7 or f/8 would be a lot easier to live with and use.

If you're thinking about an achro refractor, f/8 may also not be long enough if you're thinking about large aperture, like 150mm. The f/ratio needed to avoid humongous chromatic aberration roughly increases linearly with aperture (so the focal length increases as the square of aperture).

[sixela]

+1 about refractors, i've got a 250 skwatcher dobs and a c80 ed refracto rand despite its smallerdiameter and having half the focal length, the c80ed gives better views of planets anyday ( er any night )

Might want to have someone who's good at tweaking reflectors have a look at it (and to star test it to determine what's degrading the image). The two usual culprits are collimation (there really is no excuse for that one) and cooling, with some other possible problems (like pinching of the optics) as well.

If you don't have a fan and/or don't have the patience to wait for the 250mm Dob to cool, the 80mm ED refractor is actually the better instrument for looking at planets (if I only have 20 minutes I also don't roll out a large Dob for looking at a planet). But I doubt it can be pushed to 400x and still reveal as much detail as a well cooled and collimated 250mm Newt.

[sixela]

As for the original question:

-you need aperture. Preferably at least 200mm, but this might not be feasible (see below).

-You need tracking, whatever you get. It even trumps the above rule (I'd rather have a 150mm reflector with tracking than a 200mm reflector without tracking, when looking at planets, even though I've become good at following Jupiter around with Dobs. That's why I have a platform.)

-You need good thermal control. On a Newt, that means a fan. On a large Mak or SCT, that means a Lymax cooler. On an ED doublet refractor, that means a little bit of patience (remember not to gloat while others still have mushy images while all you have is just a wee little bit of spherical aberration).

-On any scope that has lenses at the front, you need a dew prevention solution unless you happen to live in a very dry place (reflector people, remember not to gloat or the God of Dew will curse your secondary too --eventually).

Some things are going to depend on your observational habits. A large Newtonian makes a lot more sense if you can prepare it (collimate it, run the fans) before you start observing and observe for long; it can be a GEM-mounted Newt or a Dob on a platform or with autotracking or GoTo.

An 80/100/120mm ED doublet refractors scope makes a lot more sense if you only have short observation sessions. If you only have 40 minutes and can't prepare anything, it makes little sense to have to wait for 30 minutes to observe 10 minutes well. The 120mm ED doublet refractors is already going to be quite unwieldy and is certainly not "grab'n'go", the 80mm ED doublet refractor certainly can be.

[sixela]

Bear in mind of course thet Jupiter and Saturn show very little detail relatively

That's a bit of an overgeneral statement (unless you meant it to be implicitly qualified with "with 5 inches of aperture"). Jupiter not only reveals too much detail to sketch (on some rare nights it really does look like a Hubble photo!), it also constantly changes; you can look at it for years, and finally it starts to become more interesting for Northern observers again (for years it barely lifted itself out of the "horrible seeing" soup close to the horizon).

Not to mention that there's frequently a lot happening: I have had nights in which you could see the shadow of one Galilean moon while another moon started to transit¹, with two shadows for a brief time on the disk at the same time (one clearly elongated and smaller, the other round and bigger -- Ganymedes really *is* a lot larger).

With enough aperture, the GRS these days is decidedly salmon in colour (which contrasts very nicely with the white of the trench around it and the greyish blue of the equatorial zone bulge under its leading edge); it even is strikingly coloured at 120x in my 114mm Starblast.

Even Oval BA is sometimes very reddish these days, even though there's slightly less contrast between it and the polar regions around it.

--

¹(in a large scope, it's very striking to see that the moon starts as a bright disk over a darker background, more or less disappears, and then appears once more as a dark feature over the lighter background! Jupiter really is a lot darker close to its edge, even though the eye doesn't really see it that well without extra visual cues!)

[iamjulian]

The 150PL is better for planets, and more forgiving on eye pieces, as pointed out above. But then if you want to go at deep sky objects too, and some basic astro photography, you'd be better with a stronger mount.

Personally I'd recommend all beginners to start with a basic six or eight inch dob. Though they do pretty much rule out photography. Good luck with your purchase.

[Kane]

A lot of interesting and helpful points made - the cooling aspect was one I hadn't thought about at all (I tend to be an impulsive viewer ) and the option of a larger Dobsonian hadn't occured to me either - thanks everyone