Not another "Which Telescope" thread?!

[Geesus]

Hey again all!

As I said in my title, I'm sorry to start another one of these threads (there are literally hundreds around...), but I've done some searching and all of them are geared towards an individual buying THEIR first scope, on the basis that they're interested in starting astronomy and have some money to to so. I've done a fairly thorough search both on here and google, but haven't found much!

I've just bought my first scope, a Celestron Astromaster 130 EQ-MD, and whilst I'm VERY happy with it, it's a little too big for my younger brother. (I'm 18 and 6ft 3", he's 11 in a month and too small to see through the eyepiece!).

I take him out with me most nights because I'm the best brother in the world (not at all because it's lonely in the dark on your own...), but it's his birthday soon and I'd like to get him an upgrade from the old Eduscience toy scope my girlfriend bought from a toy shop 15 years ago when she thought she wanted to be an astronaught...

I've found several here in the UK, like the little 76mm Dobs from Skywatcher and Celestron, the 50 and 70mm Travelscope refractors (come with a little backpack... not necessary but an extra I think he'd appreciate), or the various 60/70mm refractors on Alt/Az mounts from SW and Celestron... (Mercury 607 springs to mind?).

I then looked at the sale section on Orion's US website, and found these:

80mm tabletop refractor:

http://www.telescope.com/Telescopes/Sale-Telescopes/Sale-Beginner-Telescopes/Orion-GoScope-80mm-TableTop-Refractor-Telescope/pc/1/c/378/sc/436/p/9549.uts?refineByCategoryId=436

100mm tabletop reflector:

http://www.telescope.com/Telescopes/Sale-Telescopes/Sale-Beginner-Telescopes/Orion-SkyScanner-100mm-TableTop-Reflector-Telescope/pc/1/c/378/sc/436/p/9541.uts?refineByCategoryId=436

So effectively, If you had to buy a scope as a gift, with a modest budget (£50, I'm only a poor student...), taking into consideration that although he's very intelligent for his age setting up and aligning an EQ mount is COMPLETELY beyond him (size, weight, difficulty...) and he's not likely to start imaging any time soon, what would you go for? I'm more than happy to have him help me with some basic webcam imaging, but I don't think he's quite capable on his own!

Alt/Az mounts would presumably be fine as you can leave the legs extended half way, but I'd like to get him something half decent so he doesn't get bored looking at the moon for 4 hours whilst I'm trying to find DSOs, saturn, jupiter and the likes...

Is there anything out there I've missed? What would you go for?

He's quite excited by the fact that the light we can see from Andromeda has taken 2.5 million years to reach us, and is taking his pair of 10x25 Bins on his year 6 residential trip tomorrow, so I think a new scope is definitely something he'd get hours of enjoyment with, and it means I'd get to spend some big brother time with him before I leave for my gap year next january...

I'd be grateful for any thoughts/opinions!

Ginger

[Naemeth]

You could try the 78mm Mini Heritage Dobsonian (http://www.firstlightoptics.com/dobsonians/skywatcher-heritage-76-mini-dobsonian.html)

[Geesus]

Hey Naemeth!

I did look at those, but after seeing the 100mm dob from Orion in the US for not much more I was just wondering if it's possible to get anything like that here in the UK?

I know 26mm isn't much to most, but when we're talking a 33% bigger aperture It seems silly to go for the smaller if there's something else out there at a similar price?

Thanks !

Ginger

[Naemeth]

I suggested it as it's small and within budget. The other two you suggested may be available in the UK, but I'm not sure where from. You are of course right that a bigger aperture is better though.

[Black Knight]

Here's the Orion 100mm tabletop reflector (or mini-dob to the rest of us!): http://www.scsastro....p-reflector.htm. It is twice your budget though. SCSAstro are an Orion dealer in the UK.

[Naemeth]

The 130P FlexTube actually isn't that tall, and if put on a chair, I at least can sit and watch.. it might be low enough to watch if on a chair or small box... although it's a little out of budget at £135. Perhaps you may be able to get a 2nd hand one for about £100.

[Geesus]

Thanks Black Knight... I hadn't managed to find it in the UK, but it seems stupid that over the pond it's £60?! I wonder if I could order from telescope.com for cheaper...

I understand that reflectors are "light buckets", brilliant for DSOs and fainter targets, but what's the deal with planetary/lunar observation? Would he be better off with a refractor? He is interested in faint fuzzies, but being too young to operate an EQ mount and probably not experienced enough to manually locate/track something he can't see leaves me thinking he'd be better off just squeezing more detail out of already visible objects, like planets and the moon... possibly M42 and M31 etc. ?

EDIT: Hey Naemeth, I've just bought MY scope and was considering a flextube 130... It's a little out of my budget for his present unfortunately, but I agree from what I've heard it seems like it's definately one of the best value scopes out there!...

Many thanks,

Ginger

[Naemeth]

If possible, take him into an astro shop and see what height the eyepieces are at, surely that's the best way? It's just because (as far as I'm aware), all refractors are on some kind of EQ Mount.

[Geesus]

It's not the height of the mount i'm that worried about - tripod legs tend to be retractable which means with some adjustment I would be able to get the right height for him, it's more the fact that EQ mounts require balancing and polar alignment whereas Alt/Az mounts don't... Of course he'll have the opportunity to get to grips with my astromaster 130 on an EQ mount, but for his first scope I think something a little less complicated would be better!

Ginger

[Naemeth]

Hmm.. this is tricky. I'd say Reflector over Refractor due to ease of use and set-up.

[Black Knight]

It might be worth putting a Wanted ad up on ABS http://www.astrobuysell.com/uk/ saying what you want and how much you can afford to pay, and see what kind of response you get.

[Geesus]

Hey black knight - Thanks, I may do at some point! I've just had a look at everything between £40 and £50, but it doesn't look like there's much there except a Travelscope 70 for £50... I can get one for that price brand new!

Ginger

[StarryBob]

Something like this might be ok, you can use proper 1.25" EPs as well at the zoom that comes with it.

[Black Knight]

Just spotted this, but man, it's uuugly! http://www.telescopehouse.com/acatalog/Infinity_76P_3__Children_s_Parabolic_Reflector_Telescope.html

[jerryTheC]

There are basically three types of refractor around:

- extremely ropey rubbish, with horrible mounts and extremely poor lenses. These are usually sold by department stores, have Hubble pictures on the box, and quote stupidly high magnifications. Avoid these!

- achromatic refractors. These are the cheapest decent refractors, and can work nicely - but they suffer from something called 'chromatic aberation' which gives you a coloured halo (usually violet) around bright objects, because they don't focus all colours of light to the same point. How much of a halo you get depends to some extent on the design and glasses used, but is usually worse in short tube scopes than longer ones. It's a personal thing as to whether you find it annoying or not.

Apochromatic refractors - these are high end scopes that are a lot better at focusing all colours in the same place, but are going to be way out of your price range. They have arguably the best view available for a given size, but also the highest price...

Reflectors, on the other hand, since they're mirror based, focus all colours in the same place, so no problems with chromatic aberation - but they do have a central obstruction from the secondary mirror, which drops the image contrast down a bit compared to a refractor.

Basically, as long as you avoid the really bad refractors, either a refractor or a reflector can give decent views - the problem is going to be finding

something in your price range that has a big enough aperture to be useful for more than the moon.

[StarryBob]

I think you will get more for your money 2nd hand but as it's a gift you probably want new.

[Geesus]

Black Knight - I'd seen that too, but I think he'd prefer something that LOOKS professional, even if it's a long way off producing images anyone with some experience would be expecting? Not something that looks like a toy if you get my drift...

Would the Skywatcher Mercury 607 be a good choice, and how would it compare to a 76mm dob or similar?

It's achromatic, so hopefully cheap but decent, with a 60mm aperture and a focal length of 700mm. I know that with reflectors, bigger aperture is better, and I presume that the same is true for refractors (assuming lenses manufactured to the same quality), but how do the two compare? how would a mercury 60mm or a 70mm celestron travelscope refractor compare to a 76 or even 100mm reflector in terms of showing fainter objects, bringing up more detail in planets and the moon etc.?

Ginger

[cantab]

I think in part because there's no secondary obstruction a refractor can perform as well as a slightly larger reflector, provided it's good quality. I have a 60 mm refractor that's probably similar to (or a bit worse than) the Mercury 607, and it shows Jupiter's main cloud belts and Saturn's rings nicely, but not any finer detail. The Moon of course will show a lot, and even in this small scope is dazzlingly bright.

I'd suggest avoiding a photo tripod style mounting, like what the Celestron TravelScope uses; my scope is on a cheap photo tripod which is great for the binoculars, but just isn't stable or smooth enough for the scope.

[Geesus]

Okay, thanks cantab! Would you have any experience with a dob or similar reflector, and if so how would you compare ease of use?

Does your "camera style tripod" include all alt/az mounts, or just cheaper ones without eyepiece trays to help brace the legs?

Ginger

[jerryTheC]

Generally, a refractor will usually perform as well as a reflector of slightly larger aperture, since the secondary in the reflector blocks some of the incoming light. You can work out the area of the refractor lens, or subtract the area covered by the secondary from the area of the primary mirror for a reflector, which will tell you how much light gathering area you have - then, to work out how much of that light reaches the eyepiece, you need to factor in light transmission for the refractor lens, and reflectivity for the reflector mirrors (if you're using a diagonal with the refractor, you need to figure in light losses there too...)

At this point it gets a bit hazy - I think (

But could easily be wrong) that transmission for a lens is probably higher than reflectivity for a standard mirror - but lens transmission will be affected by the glass and coatings used, While mirrors can also have different coatings - so it really depends on the scope in question. Small differences in aperture aren't going to make a big difference in resolution - that's linear, while light gathering ability is squared - and may well be swamped by quality differences in the optics - with rare exceptions, very small scopes tend to be bottom end models, so the manufacturers are less likely to use best quality optics.

(one thing to watch out for - the really bad refractors sometimes have really poor lenses that give horrible colour fringing, so they fit an internal mask that reduces the effective aperture a lot to cut down the fringing - again, avoid these) (note - don't confuse this with baffles designed to cut down internal reflections from the tube walls).

[jerryTheC]

Camera tripods really don't work very well at high magnifications - cheap ones aren't hugely smooth when panning, and most tend to shift a bit when you lock the up/down movement - not a problem with normal camera lenses, or low magnification scopes, but very annoying at high powers.

On the other hand, dobsonian mounts are designed for scope use, so tend to be smoother - and since the scope tube usually extends further away from the pivot point than a tripod handle does, it's usually easier to make fine adjustments - and since the scope is usually well balanced, you don't usually need to lock it in place - which can easily result in a small shift with a photo tripod.

[cantab]

I haven't had the chance to use a Dob, no.

In my case the actual tripod is pretty stable, it's the head that has the problems. If you look at the altitude adjustment on most alt-az mounts, whether Dobsonians, the single arms common on alt-az gotos, the forks used on SCTs, or the simple "yoke" on many cheap scopes, the altitude axis goes through the middle of the scope tube. That whether the scope is pointed at the horizon, the zenith, or anywhere between it can be balanced. With a photo tripod the scope ends up above the pivot point, so it doesn't stay balanced as the scope is elevated.

[Geesus]

Okay, so any refractor with forks to hold the scope (like the one below)

would be better than, say, this:

Just trying to get my head around the differences :S.

Ginger