What's wrong with them - supermarket telescopes?

[peteyboy (Pete)]

Hi Guys

Just beginning - hence the thread!

I'm looking to buy a telescope - and given I live in the inner city, will really only be using it occasionally up bush where the lights low. I don't mind fiddling with the mount etc for an hr or so and taking a while to setup to get 'quick looks' at things, rather than setting up for an evening of viewing (at this stage). I guess I'd get the buzz from seeing Jupiter for 2 minutes, rather than tracking a whole lot of objects all night if you know what I mean.

Like most other beginners, I've looked at the Celestron range - and read vociferous and disparaging criticism of these 'supermarket' telescopes on this site, vs. the Dobs.

Reading some postings here, it would seem that having a focal length greater than the length of the telescope is one reason a cheap scope is crap, but specifically in relation to the Celestron 127mm Power Seeker (yep the DSE one), what is it technically that is no good? Is it the mount or the lens or the setup time, or the collimation (can that be sorted out?). Or is it just the sheer hassle factor of a telescope that has a suboptimal mounting system, and is hard to collimate well.

I'm happy to go to a specialist provider if I have to, but I've got to admit, like alot of other beginners, the attraction of heading down to DSE is there. If I really enjoy my foray, I'm happy to buy a better telescope off a specialist later on too. Hope that gives you experts some info on my 'needs' - looking forward to your considered replies!

Pete

[[1ponders] (Paul)]

Hi Pete and to the site. You've done the right thing first and asked the right questions.

The short answer is that if a scopes tube is much shorter than its stated focal length then there has been something added to alter the light path. What is usually added is a cheap plastic (mostly, but whether its glass or plastic its not usually of good quality) barlow type arrangement in the focuser. These usually degrade the quality of the view substantially. Also the mount that these things come on are not called Wobbletronics for nothing. Mind letting us know what sort of price these things sell for? You can by a good quality 8" dobsonian for probably around $300 that would leave the 127 for dead

[peteyboy (Pete)]

Thanks 1ponders - that's clearing thing up for me. I must admit the short scope for a big focal length did suggest to the physics kid in me some degradation was inevitable.
Price wise I think the Celestron 127mm is around $220 or so. I'd extend the 8" Dobsonian for ~ $300 if you guys reckon its much better. Am I right in saying the Dobs mount (I laughed when I saw it compared to a lazy susan in the guide on this site!) and it's non-interefered with focal length are the selling points?

[[1ponders] (Paul)]

Ok I just checked and there seems to have been a bit of a price jump in the past few months. Strange considering how much the Aus $ has gone up in comparison to the US.

Check here, you may want to consider a 6" http://www.andrewscom.com.au/site-co...-guansheng.htm which would still be much better than the 127 Celestron.

As for its good points, well it's plonk and play, no having to set your latitude and find celestial south and align your mount, no having to look through the eyepiece from under that telescope when pointed in some directions, no having to wait 15 sec for the wobbles to settle down when you adjust the focus, No having to worry about meridian flipping and finding the object again.

And the view, no comparison. And that's without the better eyepieces you would get with the dob compared to the Celestron. remember the eyepieces are half the system.

[Kal (Andrew)]

Is this the scope that DSE has? PowerSeeker 127EQ

I looked at the DSE siet and could only find the Star tracker 127 which looks quite similar.

Regarding these scopes, I honestly don't think they will be too bad. They are reflecting telescopes of 5" aperture, and they don't appear to have a built in lens to increase focal length. I don't know how good the equatorial mount will be, and that's where the dobsonian design theory comes into play. With a dobsonian, you won't have the risk of a wobbly mount because of it's simplistic design. Dobsonians will be quicker to set up, just sit it on a flat area of ground. Both equatorial and dobsonian telescopes are equal with regards to collimation - they are both newtonian reflector telescopes. The advantages of a dob become more apparent at larger sizes. You can get a 12" dob for under a grand, where if you wanted an equatorial mounted reflector telescope of the same aperture on a mount that "isn't wobbly" you will be looking at double or triple that cost.

[JethroB76 (Jeff)]

If that is the model, the focal length is twice the stated OTA length

[[1ponders] (Paul)]

Oh...and why would you want an erect imaging eyepiece.....for viewing the night sky????? I've looked through a few of these erecting eyepieces and the view is a long way from anything approaching a quality view.

[Kal (Andrew)]

Originally Posted by JethroB76

If that is the model, the focal length is twice the stated OTA length

Aaaah, gotcha, I missed the tube length info which was posted at the bottom, of 508mm, compared to the focal length of 1000mm - so it definately has a built in barlow

[[1ponders] (Paul)]

so it definately has a built in barlow

Either that or a hell of a long eyepiece extension tube

[barx1963 (Malcolm)]

Pete
A bit of practical experience may help. I was given as my first scope a 130mm Saxon Reflector on an EQ2 mount. I would probaly consider this to be a better scope than the 127 you are looking at, and was certainly more expensive! In the first 18 months of my astronomy jouney I managed to view the moon, Jupiter, Saturn, Alpha Centauri and that was about it, also spent a lot of time not finding things. I can recall spending nearly 40 minutes trying to find the Orion Neb, which I could see with the naked eye, but couldn't get that EQ mount to point at it! I then joined the ASV (Astronomical Society of Vic) and they have a loan scheme for new members where you get the use of a 8" Dob for 3 months. I was able to take it alopng to a couple of star parties and bought some atlases and was luckily allowed to extend the loan to 6 months. In that 6 months I knocked over 70+ of the Messier objects as well as several galaxies and spent hours exploring and enjoying the nights sky. I now have a 12" dob and I am very happy and exploring deeper.
The loan scope cost $10 rent with a refundable $50 deposit and was an excellent instrument. Chucked it in the back of the car several times, and never needed recollimating. Comes with a nice 8x50 finder (almost certinly better that the finder on the 127) and 25 and 10mm eyepieces. I actually found I could see more in the finderscope than I ever saw with my old scope! Add the $50 odd to join the ASV and it is excellent value. Great way to check if this hobby is really for you before forking out wads of cash.
Also feel free to get along to star parties even if you don't have a scope. Most attendees are happy to show you things and talk about their gear and give advice.
Suggest the VicSouth Little Desert party in Nov, the ASV Star-B-Que in Dec, Snake Valley next March near Ballarat are 3 I can mention of the top of my head.

Malcolm

[peteyboy (Pete)]

Thanks Barx and Kal.

I'm summarising from this the short focal length combined with a possibly crappy barlow lens is the real gotchya with these telescopes and the lens/mirror is NOT (generally speaking, at least for this brand). The upside is better light gathering power than a longer tube....so the next basic question is:

would a (physically) longer telescope, at less magnification be the go?

The Celestron 76 reflector DSE sell has 658mm optical tube and a 700mm focal length. Of course the magnification is less (the 4mm lens gives x175 instead of x250), but am I right in saying there's no (?) barlow lens, or one that won't distort too much? That telescope is only $136. The other downside I guess is it looks like the light gathering is less on the longer tube too (365 vs 265) - is that a big issue?

While I like the Dobsonian idea, they are lot dearer, and a couple of sites I checked were out of stock anyway.....yeah....call me an immediate gratification junkie, but I'm happy to fork out for a cheap 'tester' and buy a better one later.

ps. Kal - I checked and I think the difference between the StarTracker and the Powerseeker is 12mm and 20mm eyepiece vs. 4mm and 20mm eypieces respectively.

[Kal (Andrew)]

Pete, magnification is not important in a telescope. While there is a limit on how low the magnification you can get to (magnification = telescope focal length divided by eyepiece focal length), you can get any magnification you want on the other scale. Of course, you can only push that magnification up to a certain point before the image starts to degrade, and a common accepted maximum magnification that a telescope is able of producing is about 40-50 times per inch of aperture. That means for a 3" refractor you are looking at now, you will only be able to get a decent image up to about 120-150x magnification. If you want you can get 2000x magnification from it by stacking some barlows before the eyepiece, but you will see junk.

Since the amount of detail you will see in astronomy is typically determined by the light gathering abilities, or the resolution, of the optics, larger aperture scopes will nearly always show more.

Edit: BTW, I had to wait 9 years for one of my telescopes. At times I have to wait months before weather or time permits me to observe. Astronomy can definitely require patience at times

[[1ponders] (Paul)]

Here Pete, I just found this old thread. Celestron Powerseeker 127 improvements I recommend you have a good read of it and then run for the hills.

[ngcles]

Hi Pete & All,

Your thread asks the question "What's wrong with them - supermarket telescopes? "

That question requires requires a very, very long and complex reply which would take me a long time to type out and explain.

So instead I'll re-cast the question in the negative "What's right with them - supermarket telescopes?

Answer -- apart from the price-tag, virtually nothing.

Please note Paul's advice. You might at first glance be tempted to think we are being elitist and simply pooh-poohing cheap gear because we've nearly all own good gear. Not so!

Probably 30-odd% of the people in this forum started as unwary beginners and have already made the mistake you are contemplating. Almost without exception they found that while it was apparently cheap in the first instance, it became actually dear when they realised it was nearly useless and then had to then go out and buy a "proper" entry-level telescope.

Cheap supermarket-type telescopes are quite simply toys. If it's for a 5 year-old with what you believe is a passing interest in telescopes/astronomy, it will do okay.

The staff at the retailer will have no actual knowledge of the product and won't provide support to resolve your post-sale issues. All they will normally tell you (at the time of purchase) is: "this telescope is perfect for a beginning astronomer". 95% of these teleacopes are either (1) Sold at a garage sale within 18 months (2) Thrown out 18 months later, or (3) Spend 10 years lurking in a dusty corner before they are then thrown out.

Unless you really know what you are doing, buy from a retailer that specialises in or has a substantial part of their business in selling telescopes and binoculars.

If you want a difficult to use toy that provides unsatisfying views of the vast majority of celestial objects, a supermarket/ebay telescope will suit your needs perfectly.

If you decide to buy one and find it performs well below your expectations, then I suggest, at that point, that you lower your expectations.



Best,

Les D

[JethroB76 (Jeff)]

Originally Posted by peteyboy

Thanks Barx and Kal.

I'm summarising from this the short focal length combined with a possibly crappy barlow lens is the real gotchya with these telescopes and the lens/mirror is NOT (generally speaking, at least for this brand).

I think these scopes generally have a cheap/crap spherical mirror

[barx1963 (Malcolm)]

The issue I was addressing was not the optical quality. Rather the mount. For a beginner a Equatorial mount is a poor choice. The fact I could see little with my first scope was nothing to do with the optics or the OTA only the mount. If you must buy a cheapie from DSE et al. at least get one with with an alt az mount. Dobsonions are a type of alt-az mount and are gerally more robust and stable, hence easier to use.
The best advice I can give, and I think most members here will agree, that aperture (not Magnification or Focal length, or what eyepieces come with the scope) is what matters. For MOST beginners a dob as big as you can afford is perfect. Also, don't get hung up on eyepieces, my dob came with 5 and the only 2 I use are the 25mm and 32mm which give the lowest mag. I went and bought a high quality 13mm Nagler for higher power as the standard EPs that came with the scope shorter than 25 were pretty useless.
If you need one quickly, check Andrews comm in Sydney, last I heard they have plenty of stock!

[peteyboy (Pete)]

I started running for the hills half-way through the article on modifying the Celestron 127mm! It really didn't stack up given the issues people had.

To cut a long story short, I'd decided on a basic dob, but given I want to look at terrestrial objects too, the specialist I went to suggested a Saxon refractor 909EQ which I bought.

Putting it together last night was fun: the thing weighs alot and looks like a pretty solid piece of kit. Terrestrial objects come up really well - even in the hazy weather we had yesterday.

I'm still getting used to the EQ mount - which I don't mind fiddling with at all, so this weekend the thing will get a proper test-drive on the night sky and I'll report back.

[Terry B]

Good luck with the scopes.

[mswhin63 (Malcolm)]

I haven't got a 2 x Barlow but wondering if it is possible to replace the barlow in the focuser tube of the eq127 with a regular 2 x short barlow?

[bmitchell82 (Brendan)]

just make sure you point the scope directly south and put it at about 30-35 degrees. this will make sure that things will track semi alright or you can move the fine adjustments in one axis only! good luch cheif