HELP! Newbie astrotelescope cannot see anything at all

[damjandim]

Sorry for the ugly title. My dad recently bought a cheap astrotelescope online, and we are yet to get it to focus on ANYTHING at all. Here is what I know: it’s a refractor type astro telescope, with a focal length of 700mm and a lens diameter of 70mm. It features a finder scope, 3 eyepieces (20mm, 12mm and 5mm), and one extension and one barlow tube. I’m attaching images for reference.

I’ve assembled everything and I’m trying to get a look at some buildings which are pretty far away (>1km). With no eyepiece, I can see the target through the finder and through the tube of the telescope, out of focus of course but it’s there. However, with the 20mm eyepiece attached I’m moving the focusing tube back and forth with the screws which control it but nothing is changing as I look through the eyepiece, image remains totally blurred.

I’ve opened the front lens to see if there is some protective plastic there to remove, and I’ve discovered that it’s made up of two lenses and a plastic ring between them. One of the lenses is convex on both sides, and the other one is only convex on one side. I’m thinking maybe they assembled them the wrong way around in the factory or something, from what I’ve seen online the double convex lens is on the inside, then the ring between them, then the other lens with the convex side facing outwards, is that right?

That’s all of the info I can think of at the moment, if there’s anything else that might help diagnose the issue then please let me know.

[CraigT82]

Have you tried inserting the eye piece into the extension tube, then into the focuser? 

[damjandim]

Just now, CraigT82 said:

Have you tried inserting the eye piece into the extension tube, then into the focuser? 

Yeah, I have, didn’t make any difference at all. The extension tube actually has another lens inside, I’m not sure if that’s implied. The thing that bothers me is that NOTHING changes when I move the focusing tube, coming from photography this is quite inexplicable to me, I cannot understand what might be the issue.

[Anthony1979]

Or the diagnal piece

[damjandim]

Yup, tried the diagonal piece and put the same eyepiece (20mm) inside, but to no avail.

[CraigT82]

The extension tube with the lens inside will be the barlow lens, which doubles the magnification of any eyepiece inserted into it (if it's a 2x barlow). We can forget about the barlow for now!

Try aiming the scope at a far away target, inset the diagonal into the focuser, then insert the eyepiece into the diagonal, line it up using the finderscope as best as you can.  look through the eyepiece whilst racking the focuser in and out all the way.  If no image forms, try pulling the eyepiece out of the diagonal slowly and carefully whilst looking through it to see if an image forms.  If it does then you need more 'out' focus... an extension tube (without lens) will help here.

 

[Cosmic Geoff]

The 'extension tube' you describe is what we know as a Barlow lens, for giving extra magnification.

Dismantling the front lens was probably a bad move, for this is unlikely to have been the problem, and there are several ways of reassembling it in the wrong order.  (I have had a telescope with the objective the wrong way round, and it did come to focus, but performed poorly).  I suggest pointing the telescope at a bright distant light (preferably not the Sun) and trying to establish if you can get a projected image in focus on a card or wall.  If you can, then the eyepiece wants to go just behind that position by means of the diagonal piece and whatever extending parts you have to hand.

[damjandim]

 

@CraigT82 @Cosmic Geoff So I just tried what you guys suggested and here’s what I’ve found out: the two tubes are both with optics inside, one is labeled barlow the other “erection eyepiece”, whatever that means, see images. The erection one has a small lens in the center, the barlow one has a lens on the end which goes in the focuser.

I tried putting the diagonal into the focuser and then the 20mm eyepiece inside, moved the focuser all the way out, and started pulling the eyepiece out and there it was, about 10cm from the most extended position of the focusing tube I could see a focused image. I cannot believe they got it this wrong...

So, since both tubes I got have optics inside, I will need to purchase an empty extension tube to get it to work?

[Cosmic Geoff]

All rather odd. The Barlow lens in your photo looks exceptionally long.  The simplest thing to do might be to buy a 1.25" extension tube. It shouldn't cost much.  Less extension will be required if you are focusing on infinity rather than on the far end of your garden.

If you were to get the telescope to work without the diagonal, the purpose of the "erecting lens" would become evident. (The diagonal erects the image but leaves it flipped left to right.) The erector goes between the scope and eyepiece. If it contains only one lens, it is probably not a very good erector. Vintage terrestrial telescopes have a two-lens erector, while modern spotting scopes use prisms, making them a lot shorter.

Edited May 24, 2019 by Cosmic Geoff

[CraigT82]

If you can remove the lenses from either the Barlow or erection tube you should be able to use is as an extension. 

As Geoff says focusing on something closer than infinity push the focus point outwards, so using it on an astronomical target you may find the image focuses a bit further inwards

[damjandim]

@Cosmic Geoff @CraigT82 Got it, waiting and hoping for clear skies tonight, will get back to you. Thanks!

[pandoraefretum]

It's not a great scope, by the way, so don't expect much

[johninderby]

Here’s a vid showing setting up a very similar scope. 

 

[Waldemar]

When you took the front lens apart, like you wrote in your first mail, did you maybe put the inner double convex lens in in the wrong way?
That could explain the long backfocus...

[damjandim]

16 hours ago, Waldemar said:

When you took the front lens apart, like you wrote in your first mail, did you maybe put the inner double convex lens in in the wrong way?
That could explain the long backfocus...

That was my original worry as well, but my father said that when he unpacked it the front lens was already in place and he didn’t touch it, but still couldn’t achieve focus. If you or anyone else here has a correct instruction on how the lenses should be ordered, let me know so I can check.

Meanwhile, we put a piece of perfectly fitting PVC tubing between the focuser and the prism/eyepiece and now perfect focus can be achieved both near and really far off (several kilometers away). Still haven’t tried it on any planets/stars since we’ve had rain for almost a month now :(

[carastro]

The pvc tubing seems to have done the trick as an extension tube but it won’t have a small clamping bolt on it so ne careful you eyepiece doesn’t fall out snd smash. Maybe you can find a way of securing it.  

Happy viewing.  Start with the Moon. Carole